Horizontal directional drilling system and portable device and method

Abstract

A horizontal directional drilling system and a portable device and method wherein the horizontal directional drilling system includes a transmitter and a portable device, the transmitter controlling a depth signal transmit power related to a data signal transmit power such that one reception range of the depth signal at least approximately matches another different reception range of the data signal. A portable device may form a system with a transmitter in which the portable device scans a plurality of frequencies within at least one low frequency depth signal range to measure electromagnetic noise at each of the plurality of frequencies and determines the at least one frequency as a potential depth frequency for the transmitter. The portable device may include a dual mode filter having a reinforcement mode filter and a normal mode filter. The depth signal frequency may be dynamically localized relative to low frequency noise.

Description

[0001] background This application is a divisional application of the invention patent application with application number CN202110767425.5, filed on May 23, 2018, which is a divisional application of the invention patent application with application number CN201880019290.0. This application claims priority and the benefit of U.S. patent application serial number 15 / 635,884, filed on June 28, 2017, which is hereby incorporated by reference. Technical Field

[0002] The present application relates generally to the field of communications related to underground devices, and more particularly to advanced passive interference processing, apparatus and methods in directional drilling systems. Background Art

[0003] A technique for installing utilities without digging trenches is often referred to as horizontal directional drilling (HDD). A typical utility installation includes the use of a drill rig with a drill string that supports a boring tool at the far or underground end of the drill string. The drill rig pushes the boring tool through the ground by applying thrust to the drill string. As the drill string is extended, the boring tool is turned to form a pilot bore. When the pilot bore is completed, the far end of the drill string is attached to a pullback apparatus, which in turn is attached to the front end of the utility. The pullback apparatus and the utility are then pulled through the pilot bore by the retraction action of the drill string, thereby completing the installation. In some cases, the pullback apparatus may include a back reaming tool for expanding the diameter of the pilot bore in front of the utility so that the diameter of the installed utility is larger than the initial diameter of the pilot bore.

[0004] The steering of the boring tool can be achieved in a known manner by orienting the asymmetric face of the boring tool to deflect in the desired direction underground in response to forward movement. In order to control the steering, it is necessary to monitor the direction of the boring tool based on sensor readings obtained from a sensor, which forms part of an electronic package supported by the boring tool. For example, the sensor readings can be modulated onto a positioning signal emitted by the electronic package to be received by a portable locator or other suitable ground device above the ground. In some systems, the electronic package can couple a carrier signal modulated by the sensor readings to the drill string, and then transmit the signal to the drill rig by using the drill string as an electrical conductor. Regardless of the transmission method of the sensor data, for a given amount of transmission power, there is a limited transmission range in which the sensor data can be recovered with sufficient accuracy. The transmission range can be further limited by active interference and passive interference. Active interference generally includes an electromagnetic signal source that appears in the operating area, which can cover the signal transmitted by the system. In contrast, passive interference is used to block or distort the transmission signal, which may result in a reduced range or, in some cases, inaccurate readings. A common source of passive interference is rebar. In addressing the deficiencies of the prior art, the applicant filed U.S. Patent Application No. 14 / 845,231 (hereinafter referred to as the '231 Application') entitled "Communication Protocol, Apparatus and Method for Transmission of Multi-bit Data Symbols in Directional Drilling Systems", which belongs to the same applicant as the present application and is incorporated herein by reference in its entirety. The '231 Application provided revolutionary benefits over the prior art at the time and continues to provide such improvements, however, the present application discloses further improvements, particularly regarding improvements in passive interference, which will be discussed in detail below where appropriate.

[0005] The foregoing examples of the related art and limitations therewith are intended to be illustrative rather than exclusive. Other limitations of the related art will become apparent to those skilled in the art after reading the specification and studying the drawings. Summary of the invention

[0006] The following embodiments and aspects thereof are described and illustrated in an exemplary and illustrative (but not limiting) manner in conjunction with systems, tools and methods. In various embodiments, one or more of the above problems have been reduced or eliminated, while other embodiments are intended to obtain improvements in other aspects.

[0007] One aspect of the present application describes a transmitter and related methods for use in conjunction with a horizontal directional drilling system. The horizontal directional drilling system includes a drill string extending from a drill rig to an underground tool, the underground tool supporting the transmitter so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations. The transmitter includes an antenna and one or more sensors for generating sensor data. The antenna driver electrically drives the antenna to transmit a depth signal in response to a depth drive input for above-ground reception in determining the depth of the underground tool, and electrically drives the antenna to transmit at least one data signal representing sensor data using at least one data signal frequency in response to the data drive input for above-ground recovery of the sensor data, the data signal frequency being higher in frequency than the depth signal. A processor generates a depth drive input at a depth signal frequency, and generates a data drive input to characterize the sensor data in a manner that controls a depth signal transmission power related to the data signal transmission power so that a reception range of the depth signal at least approximately matches another different reception range of the data signal.

[0008] In another aspect of the present application, the antenna driver electrically drives the antenna to transmit a depth signal in response to a depth drive signal for above-ground reception to determine the depth of an underground tool, and electrically drives the antenna to transmit a data signal representing sensor data using at least one data signal frequency for above-ground recovery of the sensor data, the data signal being higher in frequency than the depth signal. The processor is configured to generate the depth drive signal at the depth signal frequency, and is configured to generate the data drive signal at the data signal frequency to control a first reception range of the depth signal to be related to a second reception range of the data signal.

[0009] In yet another aspect of the present application, a system, a portable device, and an associated method are described. In the system, a transmitter is used to move through the ground in an area during an operation process while transmitting a depth signal at a depth frequency selectable within a depth signal frequency range below 1 KHz to provide at least some immunity to passive interference, the depth frequency also being affected by electromagnetic noise that can vary within the area. The portable device is used to scan a plurality of frequencies within the depth signal frequency range to measure the electromagnetic noise at each of the plurality of frequencies, and to determine the lowest frequency of the frequencies as a potential depth frequency, the depth potential frequency meeting a low noise requirement based on the measured noise.

[0010] In another aspect of the present application, a portable device is provided as part of a system in which a transmitter is used to move through the ground in an area during an operation process while transmitting a depth signal. The portable device includes an antenna for receiving the depth signal to generate an output. A receiver is used to measure electromagnetic noise based on the antenna output in at least two different frequency bands below 1 KHz by gradually scanning each frequency to generate a plurality of incremental noise readings in each frequency band, and display one or more potential depth frequencies for each frequency band for an operator to select based on the incremental noise readings.

[0011] Another aspect of the present application describes a system and associated method in which a transmitter is used to move through the subsurface of an area during an operation while transmitting a depth signal at a depth frequency selectable within a range of depth signal frequencies below 1 KHz to provide at least some immunity to passive interference, the depth frequency also being affected by electromagnetic noise that can vary within the area. A portable device is used to measure electromagnetic noise based on an antenna output in at least two different frequency bands below 1 KHz by progressively scanning each frequency to generate a plurality of incremental noise readings in each frequency band, and to display one or more potential depth frequencies for each frequency band for selection by an operator based on the incremental noise readings.

[0012] Another aspect of the present application describes a portable device and an associated method as part of a system. In the system, a transmitter is used to transmit a depth signal at a depth frequency and a data stream at one or more data frequencies while moving through the ground in an area during operation, the data stream representing at least an orientation parameter of the transmitter. The portable device includes an antenna for receiving the depth signal and the data frequency to generate an output. A switchable filter portion is used to limit the antenna output in normal mode to a frequency band above a predetermined frequency so as to transmit the depth signal and the data stream at one or more frequencies, and to limit the antenna output in rebar mode to another frequency band so as to transmit the depth signal at a frequency below the predetermined frequency and to transmit a data stream containing one or more frequencies above the predetermined frequency. A processor is used to switch the switchable filter portion between normal mode and rebar mode to recover the depth signal and the data stream in response to selection of normal mode and rebar mode.

[0013] Another aspect of the present application describes a system, method, and apparatus wherein a transmitter is used to move through the ground in an area during operation while transmitting a depth signal at a selectable depth signal frequency, the selectable depth signal frequency being set to any one of a plurality of incrementally spaced frequencies within a depth signal frequency range below 1 KHz to provide at least some immunity to passive interference, the depth signal also being affected by low frequency electromagnetic noise below 1 KHz that can vary within the area, and for transmitting a data signal characterizing at least the orientation of the transmitter within a data frequency range above 1 KHz. A portable device is used to scan the plurality of incrementally spaced frequencies below 1 KHz to measure the electromagnetic noise at each of the plurality of incrementally spaced frequencies for identifying at least one low noise frequency associated with the low frequency noise when the depth frequency is set in the transmitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Exemplary embodiments are shown in the reference figures accompanying the specification. The embodiments disclosed herein and the figures are intended to be illustrative rather than limiting.

[0015] Figure 1 is a schematic view of one embodiment of a system for performing underground operations according to the present application.

[0016] Figure 2 is a partial cross-sectional view of a perspective view of an embodiment of a transmitter made in accordance with the present application.

[0017] Figure 3 It shows about Figure 2 A block diagram of an embodiment of a transmitter with additional details.

[0018] Figure 4 is a detailed block diagram of an embodiment of a frequency synthesizer, the frequency synthesizer forming Figure 2 and Figure 3 Part of an implementation of a transmitter.

[0019] Figure 5a is a graphical representation of a lookup table that can be used to Figure 4 Depth and symbol frequency lookup table shown.

[0020] Figure 5b is a graphical representation of an implementation of an antenna drive waveform based on increasing frequencies; Figure 5c is a graphical representation of one embodiment of transmitter frequency bands used in rebar mode; Figure 6a is a graph of the power spectral density of the noise obtained at high resolution, corresponding to the actual physical location using a 50 Hz power line frequency.

[0021] Figure 6b is a schematic diagram showing one embodiment of a screen shot of a display 36 including a bar graph showing Figure 5b Average noise per frequency sub-band for an embodiment of the transmitter frequency band shown in FIG.

[0022] Figure 6c is a schematic diagram showing another embodiment of a screen shot of a display 36 including a bar graph showing the state of the display 36 in the reinforcement mode. Figure 5c Measured noise of a noise scan of an implementation of the transmitter frequency band is shown in FIG.

[0023] Figure 7 Is from Figure 6a A further enlarged view of sub-band 10 of FIG. 1 is shown here to facilitate discussion of portions of the depth frequencies and symbol frequencies.

[0024] Figure 8 is a flow chart showing one embodiment for operating a transmitter according to the present application; Figure 9a It is shown Figure 1 a block diagram of an embodiment of the portable device shown; Figure 9b It is schematically shown Figure 9a A graph of one embodiment of a normalized filter response for a normal mode filter is shown.

[0025] Fig.9c It is schematically shown Figure 9a A graph of an embodiment of the normalized response of a rebar pattern filter is shown.

[0026] Fig.10a Is from Figure 6a Expanded diagram of frequency sub-band 6.

[0027] Fig.10b is a schematic diagram of one embodiment of a screen shot showing the appearance of sub-band 6 on a display screen for the purpose of operator selection and modification of symbol frequencies, as well as other functions in accordance with the present application.

[0028] Fig.11 yes Fig.10a and Fig.10b A further enlarged view of a portion of subband 6 of is shown here for the purpose of describing further details regarding the symbol frequency selection.

[0029] Fig.12a is a flow chart illustrating an embodiment of a method for operating a portable device in a normal mode for the purpose of performing spectrum scanning and frequency allocation according to the present application.

[0030] Figure 12bis a flow chart illustrating another embodiment of a method for operating a portable device in a dry rebar mode for the purpose of performing spectrum scanning and frequency allocation according to the present application.

[0031] Fig.12c is a flow chart illustrating yet another embodiment of a method for operating a portable device in a rebar mode for the purpose of performing spectrum scanning and frequency allocation according to the present application.

[0032] Fig.12d is a flow chart illustrating yet another embodiment of a method for operating a portable device in a rebar mode for the purpose of performing spectrum scanning and frequency allocation according to the present application.

[0033] Fig.12e is a flow chart illustrating yet another embodiment of a method for operating a portable device in a rebar mode for the purpose of performing spectrum scanning and frequency allocation according to the present application.

[0034] Fig.13 is a flow chart illustrating an embodiment of a method of operating a portable device for receiving a depth signal and a data signal during underground operations according to the present application. DETAILED DESCRIPTION

[0035] The following description may enable a person of ordinary skill in the art to make and use the invention, and is also provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the basic principles taught herein may also be applied to other embodiments. Therefore, the present invention is not intended to be limited to the illustrated embodiments, but is to be given the widest scope consistent with the principles and features disclosed herein (i.e., including various modifications and equivalents). It should be noted that the drawings are not drawn to scale, and are essentially schematic in nature to best illustrate the features of interest. Descriptive terms are used to improve the reader's understanding of the different views provided in the drawings, but they do not limit the scope of the invention in any way.

[0036] By way of introduction, the applicant has recognized that, although the prior art attempts to address the problem of passive interference caused by, for example, steel bars, it still requires improvement. The applicant believes that passive interference is a persistent problem that represents one of the most challenging problems that must be overcome on a construction site in addition to active interference, and that, to date, the prior art has not yet addressed the problem to an acceptable degree. Now, the applicant has recognized that the reception of electromagnetic signals for the purpose of determining the depth and position of an underground transmitter is affected in one way by passive interference, while the reception of electromagnetic signals for the purpose of recovering a data stream from an electromagnetic signal characterizing the direction and other parameters of the buried transmitter is affected in a completely different way. In this regard, the determination of the depth and position of the buried transmitter depends on the shape and signal strength of the electromagnetic field or magnetic flux lines of the electromagnetic signal. However, the field shape of the electromagnetic signal may be deformed by the influence of electrical conductors, such as steel bars. Such deformation may result in inaccurate determination of the depth and position. Although the deformation can be reduced by reducing the frequency of the electromagnetic signal, the applicant has recognized that the deformation has little effect (if any) in recovering the data stream or data from the electromagnetic signal characterizing the direction of the buried transmitter. That is, data can be decoded from higher frequency electromagnetic signals regardless of field deformation as long as there is sufficient signal strength to decode the received signal. Therefore, the applicant has found that separating frequencies that are considered to be ultra-low depth frequencies (e.g., equal to or lower than 1KHz or equal to or lower than 1.5KHz) from one or more data signal frequencies can make the depth frequencies less affected by passive interference than higher data signal frequencies (which are higher than any suitable frequency threshold or limit, such as higher than 1KHz or 1.5KHz), while in terms of field shape, higher data signal frequencies are more affected by passive interference than depth signal frequencies, but despite the additional field deformation during passive interference, the former is still used to transmit data streams. At the same time, this low frequency range may be too noisy. The applicant solves this problem based on further scanning the electromagnetic noise in an appropriate low frequency band (e.g., from the power line frequency to an appropriate frequency upper limit such as 1KHz or 1.5KHz) to determine that one or more frequencies in the low frequency band are noise-free or even relatively low noise, thereby avoiding the presence of excessive noise. The applicant believes that the combination features disclosed above and elsewhere in this article are not seen in the prior art, and the reason for this is at least because the general understanding of the prior art is that ultra-low frequencies (e.g., equal to or lower than 1KHz or 1.5KHz) are not used as depth frequencies due to the high active interference at such low frequencies. In other words, in order to receive low-frequency depth signals, ordinary technicians in this field will abandon the use of such uncontrolled low frequencies because it will generate additional low-frequency active interference, which may prevent the system from receiving depth signals (possibly even data signals). The present application submitted by the applicant does not have the problems of the prior art.For the purposes of this application, a bit is a binary data value having two states characterized as 1 / 0, + / -, etc. For the purposes of this application, a symbol is a data value representing one or more bits. A multi-bit symbol represents two or more bits. The symbol may represent any suitable type of information, such as pitch data, roll data, temperature data, battery data, and synchronization data, but is not limited thereto. Different multi-bit symbols represent different multi-bit data values. For example, 16 different symbols may represent four-bit data values. For the purposes of this application, each multi-bit symbol is represented by a unique frequency that is different from the frequency associated with any other multi-bit symbol. A symbol stream consists of a serial transmission of multi-bit symbols so that the symbol stream can be decoded into a corresponding digital data stream (which may be binary). The symbol stream may be sent according to a packet structure so that the specific position of a given symbol within the packet structure defines the data type associated with the symbol.

[0037] Referring now to the drawings, wherein like parts are designated by like reference numerals throughout the several views, attention will be immediately directed to Figure 1 , Figure 1 One embodiment of a system for performing underground operations is shown, generally indicated by the reference numeral 10. The system includes a portable device 20, which is shown as being held by an operator above the surface 22 of the earth, and is also shown in a further enlarged inset view. It should be noted that only limited inter-component wiring is shown within the device 20 to maintain clarity of the view, but it should be understood that all necessary cables are present and can be easily implemented by a person of ordinary skill in the art after considering the entire application. The device 20 includes a three-axis antenna cluster for measuring three orthogonally arranged components of magnetic flux. U.S. Patent No. 6,005,532 discloses an embodiment of a useful antenna cluster contemplated for use herein, which patent and the present application belong to the same applicant and are incorporated herein by reference. Detailed description of the embodiments of the antenna used herein will be given below at appropriate locations. The antenna cluster 26 is electrically connected to the electronic part 32. A tilt sensor device 34 can be provided to measure the gravity angle, from which the flux components in the horizontal coordinate system can be determined. As a non-limiting example, a suitable tilt sensor may include a three-axis accelerometer.

[0038] The device 20 may also include a graphic display 36 and a telemetry antenna 40, which can transmit or receive telemetry signals 44 for data communication with the drilling rig. It should be understood that the graphic display 36 can be a touch screen to facilitate the operator to select various buttons defined on the screen, and / or can conveniently scroll between various buttons defined on the screen for the operator to select. Such a touch screen can be used alone or in combination with an input device 48 (such as a trigger button). The input device can be used without a touch screen. In addition, the input device can have many changes, and a scroll wheel or other suitable form of selection device that is now available or to be developed can be used. The electronic part can include such components, such as one or more processors, any suitable type of memory, antenna driver and analog-to-digital converter. As is known in the art, the latter should be able to detect frequencies that are at least twice the highest frequency of interest. Other components can be added as desired, such as a magnetometer 50 and an ultrasonic transducer, the former helping to determine the position relative to the drilling direction and the latter measuring the height of the device above the surface.

[0039] Still see Figure 1 , the system 10 also includes a drilling rig 80 having a carriage 82 that receives movement along the length of a pair of oppositely disposed rails 84. An underground tool 90 is attached to the opposite end of the drill string 92. As a non-limiting example, the underground tool is shown as a drilling tool and is used as a frame described in the present application, but it should be understood that any suitable underground device, such as a reaming tool or a mapping tool used during a pull-back operation, can be used. Generally, the drill string 92 is composed of a plurality of removably attachable drill pipe sections so that the drill rig can advance the drill string underground using movement in the direction of arrow 94 and can retract the drill string in response to movement in the opposite direction. The drill pipe sections define a channel for conveying drilling mud or fluid discharged from the drilling tool under pressure to help drill through the ground and cool the drill bit. Typically, the drilling mud is also suspended along the outer length of the drill string and carries drill cuttings to the surface. Steering can be achieved by orienting the asymmetric surface 96 of the drilling tool to deflect in the desired direction underground in response to a forward, propulsive movement that can be referred to as a "propulsion mode." Rotating or revolving the drill string 98 by the drill rig typically results in the boring tool advancing forward or in a straight line, which may be referred to as a "rotate" or "advance" mode.

[0040] The drilling operation may be controlled by an operator (not shown) at a console 100, which itself includes a telemetry transceiver 102 connected to a telemetry antenna 104, a display screen 106, an input device (e.g., a keyboard 110), a processing device 112 (which may have an appropriate interface, memory, and one or more processors). A plurality of joysticks 114 may, for example, control the movement of the carriage 82. The telemetry transceiver 104 may transmit or receive telemetry signals 116 to facilitate two-way communication with the portable device 20. In one embodiment, the screen 106 may be a touch screen, so that the keyboard 110 may be optional.

[0041] In one embodiment, the device 20 is used to receive an electromagnetic depth signal 120 and an electromagnetic data signal 122 transmitted from a transmitter 130 supported in a drilling tool or other underground tool. These signals may be collectively referred to herein as transmitter signals. The transmitter signal may be a dipole signal. It should be understood that the portable device may be used in a manner such as Figure 1 The portable device may be operated in a walkover locating mode as shown, or the portable device may be operated in a homing mode as shown in U.S. Patent No. 9,540,879 (which is assigned to the same applicant as the present application and is incorporated herein by reference in its entirety), in which the portable device is placed on the ground. Although the present application shows a dipole locating field emitted from a drilling tool and rotated about the symmetry axis of the field, the present application is not limited thereto.

[0042] The information carried by the data signal may include, but is not limited to, position orientation parameters based on pitch and roll orientation sensor readings, temperature values, pressure values, battery status, tension readings in the context of a pullback operation, etc. As will be further described, the device 20 receives the transmitter signal using the antenna array 26 and processes the received data signal 122 to recover the data.

[0043] Figure 2 1 is a schematic partial cross-sectional view in perspective showing one embodiment of a transmitter 130. The latter includes a main housing 134 which may be of at least generally cylindrical configuration. A battery compartment 138 may be formed at one end of the housing, with the opposite end supporting a main printed circuit board (PCB) 144 which may itself support an antenna 148 for transmitting transmitter signals. An accelerometer module 150 may be placed adjacent one end of the PCB 144. As will be further described, other sensors and components may be located on the main printed circuit board.

[0044] Now combine Figure 2 Turn your attention to Figure 31 to describe additional details about an embodiment of the transmitter 130. The transmitter includes a processing portion 152 that receives sensor information via a multiplexer 154. The multiplexer can be connected to any number of sensors that form a sensor suite. In this example, the sensor includes a Figure 2 The accelerometer 158 in the accelerometer module 150 of the present invention, the pressure sensor 160 that can be used to sense the annular pressure around the transmitter within the borehole, the temperature sensor 164, the battery current sensor 168 and the battery voltage sensor 170. In some embodiments, external communication for the transmitter can be provided through the external communication connection 174. Such communication does not need to be transmitted through the ground, but can be carried out when the transmitter is above the ground (for example, the transmitter is adjacent to the device 20). External communication can be implemented in any suitable manner, including but not limited to IrDA, NFC, Wi-F, Zigbee or Bluetooth. The power supply section 178 can include a battery 180 that is powered by an overvoltage and reverse polarity detector 184. The latter provides power to a logic and sensor power supply 188 and an antenna drive power supply 190. The aforementioned logic and sensor power supply provides power to the sensor suite and the processing section 152. The aforementioned antenna drive power supply feeds power to the depth antenna driver 194 and the data antenna driver 198, which electrically drive the two opposite ends of an antenna coil, forming part of the antenna 148. In one embodiment, drivers 194 and 198 may be half-bridge drivers. The antenna driver receives an input signal from a processor 200, which forms part of a processing portion. The processing portion also includes, for example, an oscillator 210 (such as a crystal oscillator). The oscillator may be selected to provide relatively high temperature and overall stability. The processor (CPU) 200 includes a timer portion 212, which may be used to generate a reference signal having stability that reflects the stability of the oscillator 210. The output frequency of the timer may be selected based on a user-specified reload timer value. The processor is in data communication with a memory 218, which may include any suitable information, including but not limited to depth frequency information 224 and symbol frequency information 228, which will be described at appropriate locations below.

[0045] Go to Figure 4 , one embodiment of a frequency synthesizer is generally indicated by reference numeral 300 and is Figure 3 It is understood that the frequency synthesizer can be implemented in hardware, software or any suitable combination. The frequency synthesizer can be implemented in any suitable implementation currently available or not yet developed. Figure 4 The embodiment of the invention is a two-channel direct digital synthesizer (DDS) having a depth channel 304 and a sign channel 308. The depth channel Figure 3The depth driver 194 provides an output signal 310 to generate the depth signal 120, while the sign channel provides an output signal 310 to generate the depth signal 120. Figure 3 The data driver 198 provides an output signal 312 to generate the data signal 122 (see Figure 1 and Figure 2 ). The depth channel waveform lookup table portion 320 and the sign channel waveform lookup table portion 324 each include at least one waveform or phase lookup table that characterizes one cycle of a selected waveform (e.g., a sine wave). In another embodiment, each of the depth channel lookup table portion 320 and the sign channel lookup table portion 324 may include multiple waveform or phase lookup tables. In this example, a waveform lookup table represented by reference numeral 326 is schematically shown in each of the depth channel lookup table portion and the sign channel lookup table portion. It should be understood that any desired one or more waveforms can be characterized by a lookup table. In addition, it is not required that (multiple) depth channel lookup tables and (multiple) sign channel lookup tables characterize the same (multiple) waveforms. In some embodiments of the frequency synthesizer, a lookup table is not required. For example, a suitable mathematical expression can be used.

[0046] Figure 5ais a diagrammatic illustration of a lookup table 326, which may include a large number of samples of characteristic waveform amplitudes based on, for example, the amount of available storage and the resolution required. In this embodiment, it is assumed that the depth channel and the sign channel use the same lookup table, and it should be understood that only a single copy needs to be stored for access by both channels. In this embodiment, the lookup table 326 represents one cycle of a sine waveform. The vertical axis represents the pulse width modulation (PWM) percentage, with the positive waveform peak being 100% and the negative waveform peak being 0%, for reasons not yet described. The horizontal axis in the figure represents the time slot, so that a given time slot has an associated amplitude. The time slot value can be referred to as a sample, which is selectively addressed by the depth channel phase accumulator 330 and the sign channel phase accumulator 334, respectively, using an m-wide addressing arrangement. Note that a very large number of samples can be associated with the lookup table. Each phase accumulator is used to provide an output count to the lookup table portion based on the input increment or offset size provided by the depth channel frequency control 338 and the sign channel frequency control 340, respectively. Each phase accumulator generates what can be described as a quantized sawtooth waveform output, where the output changes from one level or count to the next level or count corresponding to a corresponding one of the input increment sizes. In response to each corresponding phase accumulator input count, the lookup table 326 sequentially generates a digital output amplitude received by the depth channel pulse width modulator (PWM) generator 350 and the sign channel pulse width modulator (PWM) generator 352 on an n-wide addressing arrangement for either the depth channel or the sign channel, respectively. Based on the amplitude value received by each PWM generator, the pulse width modulator generates an output pulse train having a substantially constant output amplitude, but with a pulse width that increases in proportion to the output amplitude value from the lookup table. The waveform can be smoothed to approximate a desired output waveform, such as a sine waveform, by filtering through the inductive characteristics of the antenna 148.

[0047] Still see Figure 4, each of the depth channel output waveform 360 and the symbol channel output waveform 362 can be generated with high accuracy in a frequency range of, for example, close to 0 Hz to 45 KHz. It should be understood that any suitable frequency range can be used, and the range of 0 to 45 KHz is described as an example, but is not intended to be limiting. In the present embodiment, the accuracy can be at least + / - 0.1 Hz or less at a resolution of at least about 5 Hz. Note that in the context of the present embodiment, a specific accuracy is specified for at least about 45 KHz, which represents the lower limit of the accuracy in the entire frequency range. Compared with the prior art method, it should be understood that the present application provides higher accuracy, greater consistency and significant flexibility regarding the frequency position over the entire transmission bandwidth. Based on the input increment size provided to the depth channel phase accumulator 330 via the depth channel frequency control 338 and to the symbol channel phase accumulator 334 via the symbol channel frequency control 340, the output frequencies 360 and 362 are determined. The depth channel frequency control 338 receives a depth frequency input 368, which specifies the depth frequency. The depth channel frequency control may convert a specified depth frequency into an increment size for the depth channel phase accumulator 330 in any suitable manner. In one embodiment, the depth channel frequency control may include an increment lookup table 370 that indexes the depth frequency according to the increment size. In another embodiment, the increment size may be determined using the following formula: Increment size = (desired frequency) × phase accumulator size / (phase accumulator update rate) (Equation 1) The phase accumulator size is selected to provide the minimum required frequency resolution, and the phase accumulator update rate is determined by timer 212 (see Figure 3 ) is determined. Similarly, the symbol channel frequency control can convert the specified symbol frequency received on the data symbol stream input 374 to an increment size for the symbol channel phase accumulator 334 in any suitable manner, such as by using an increment lookup table 370 or a formula. The origin of the data symbol stream of the data symbol stream input 374 will be described below at an appropriate location. Note that it is not required that the depth channel frequency controller and the symbol channel frequency controller use the same increment size lookup table. Table 1 below shows a portion of one embodiment of the increment lookup table 370.

[0048] Table 1: Desired output frequency vs. phase accumulator size increment Desired output frequency (Hz) Phase accumulator size increment (counts) 5 1 50 10 500 100 32770 6554 45000 9000 Based on Table 1, it will be appreciated that a high degree of resolution is provided for each of the optional frequencies in the depth output frequency 360 and the symbol output frequency 362. In the present embodiment, a resolution of 5 Hz can be provided over the entire frequency range extending from the worldwide AC power line frequency to 45 KHz. Of course, other embodiments may use similar or different resolutions for even higher frequencies. Other resolutions may be used, some of which are larger, and some of which are even finer, but the applicant recognizes that 5 Hz represents a relatively small common multiple of 50 Hz and 60 Hz, which are the main power line frequencies around the world. Power line frequencies will be further described below.

[0049] Continue to see Figure 4It should be understood that the depth output frequency 360 and the symbol output frequency 362 are shown as frequency modulations having a finite or fixed duration, at least substantially fixed frequency, and may include variable amplitudes. In this regard, primary amplitude control may be provided according to a multiplier, which may be specified by a multiplier table 376 accessible to both the depth channel frequency control 338 and the symbol channel frequency control 340. The multiplier specifies a range of 0 to 1.0. In order to generate the desired transmission power for the specified frequency, the samples obtained from the lookup table 326 are multiplied by the multiplier. Thus, a multiplier of 1.0 produces a maximum amplitude or 100% amplitude, while a multiplier of 0 produces a zero output. As will be further described, the multiplier table may be used to compensate for changes in the coupling between the antenna and the drive circuit and changes in the antenna impedance in response to changing frequencies. Likewise, if the same table is used for both channels, only one copy of the multiplier table needs to be stored. In addition, amplitude / amplitude shaping can be implemented using a depth channel waveform / amplitude control 380 for the depth channel, which can be referred to as a depth channel shaper, and a symbol channel waveform / amplitude control 382, ​​which can be referred to as a symbol channel shaper. In another example, the output of the depth channel PWM generator 350 is a continuous depth signal 386, whose amplitude is at least substantially continuous. In this case, a depth channel shaper may not be required, although it should be understood that its operation reflects the operation of the symbol channel shaper, as described herein. It should be understood that the depth of the transmitter based on the depth signal 386 can be determined based on the well-known dipole equation, such as described in U.S. Patent No. 5,633,589, which is incorporated herein by reference. Another example output 390 of the symbol channel PWM generator 352 shows a series of output signals, which are represented by 392a-392f and can vary in frequency from one symbol to the next. As will be further described, the output 390 can include a stream of symbols. In the present embodiment, there is no gap or space of zero amplitude between adjacent symbols or there is no gap or space of zero amplitude inserted between adjacent symbols by phase accumulator 334. Therefore, the frequency can change suddenly from one symbol to the next symbol in a way that can introduce noise in response to such sudden frequency conversion. It should be understood that the symbols 392a-392f are shaped in such a way that sudden frequency transitions are avoided by starting and ending with values ​​that are approximately zero amplitude. This shaping can be achieved by applying an appropriate window or cone function by the symbol channel shaper 382, ​​such as a Hamming window, a Hann window, a Welch window, or a triangular window, etc. What is common to all object window functions is that the zero amplitude of the waveform for any point pair outside the window interval causes each symbol to start and end with a zero amplitude waveform.

[0050] Now combine Figure 2 , Figure 4 and Figure 5a Direct your attention to Figure 5b and Table 2. Although not required, embodiments of the transmitter 130 may be configured to transmit the depth signal 120 and the data signal 122 using a range of transmitter frequency bands generally indicated by reference numeral 400 extending from approximately 0 to 45 KHz, such as Figure 5b As shown. It will be appreciated that other embodiments may use different transmitter frequency bands and sub-bands, and this embodiment uses them as a non-limiting example. Although the value of zero is listed as the lower limit, it will be appreciated that the actual lower limit may be represented by the predominant power line frequency throughout the world or some higher value. The transmitter frequency bands are denoted BT1-BT5 and are also listed in Table 2. Although Figure 5b The descriptive framework used in Table 370 and Table 2 uses a transmitter band including frequency sub-bands, but it should be understood that the band / sub-band nomenclature may be changed in any suitable manner as long as there is an appropriate correspondence with the last column of Table 2 including multiplier table 376. It should be noted that in the illustrated embodiment, the values ​​of the multipliers in multiplier table 376 gradually increase from one sub-band to the next, which is also reflected by Figure 5b The gradually increasing amplitude of the sub-band waveforms 402a-402j is reflected. In another embodiment, each sub-band waveform 402a-402j can be a separate lookup table, thereby forming a set of lookup tables, rather than using a multiplier table with a single lookup table. In yet another embodiment, since the multiplier can be specified as, for example, a function, it is not necessary to define the frequency bands or sub-bands. As described above, there is no need to use a lookup table. For example, in one embodiment, an expression in the form of a linear function can be used, which can give a substantially continuous change in the multiplier value at the transmit frequency resolution of the transmitter. For example, other functions can be generated using an appropriate curve fitting method (such as the least square method).

[0051] Table 2: Transmitter frequency bands and sub-bands Transmitter frequency band Frequency band range Subband number Subband frequency range Multiplication table 376 BT1 0 to 4.5 KHz SB1 0 to 4.5 kHz 0.34 BT2 4.5 KHz to 9 KHz SB2 4.5 KHz to 9 KHz 0.45 BT3 9 KHz to 18 KHz SB3 9 KHz to 13.5 KHz 0.55 BT3 9 KHz to 18 KHz SB4 13.5 KHz to 18 KHz 0.63 BT4 18 KHz to 31.5 KHz SB5 18 KHz to 22.5 KHz 0.70 BT4 18 KHz to 31.5 KHz SB6 22.5 KHz to 27 KHz 0.75 BT4 18 KHz to 31.5 KHz SB7 27 KHz to 31.5 KHz 0.82 BT5 31.5 KHz to 45 KHz SB8 31.5 KHz to 36 KHz 0.86 BT5 31.5 KHz to 45 KHz SB9 36 KHz to 40.5 KHz 0.92 BT5 31.5 KHz to 45 KHz SB10 40.5 KHz to 45 KHz 1.00 Still see Figure 5bAccording to this embodiment, the frequency range from 0 to 45KHz is further divided into 10 sub-bands SB1-SB10, each sub-band having a width of 4.5KHz. Each frequency band above BT1 and sub-band 1 can be regarded as containing its lower frequency limit. Although not required, the use of transmitter bands enables management of transmission efficiency and transmission power. Although transmitter bands BT1 and BT2 each include a single sub-band, it should be noted that transmitter band BT3 includes two sub-bands SB3 and SB4, transmitter band BT4 includes three bands SB5-SB7, and transmitter band BT5 includes three sub-bands SB8-SB10. According to a transmitter of one embodiment of the present application, it can be configured to transmit a depth signal 120 and a data signal 122 in a single sub-band. In another embodiment, the transmitter can be configured to transmit the depth signal 120 in a frequency band that is not continuous with the frequency band used for the data signal 122. In this regard, it should be understood that a separate synthesizer channel is used for the depth channel (see Figure 4 ) provides a great degree of flexibility with respect to the frequency of the depth signal relative to the data signal. In a wideband transmitter, as described further below, the transmitter may transmit on two or more frequency bands, such that frequency bands may even be separated by other frequency bands.

[0052] In some embodiments, the transmitter 130 can be configured to cooperate with the antenna 148 so that the transmitter transmits over a wide frequency range or band extending from the lowest frequency to about 45KHz or higher. In this way, the wide frequency band can be covered by a single broadband transmitter using a single antenna, while maintaining appropriate efficiency in power consumption over the entire wide frequency range. In order to transmit over the entire frequency range from the lowest frequency to about 45KHz, as a non-limiting example, the implementation of the multiplier table 376 can be configured to include any suitable number of values. The depth channel phase accumulator 330 and the symbol channel phase accumulator 334 can be configured to utilize appropriate entries in the multiplier table 376 based on the frequency to be generated. In this way, regardless of the transmission frequency, at least approximately constant power consumption can be maintained over the entire wide transmission bandwidth. In the prior art, given a constant drive voltage and waveform, otherwise the transmitter will consume more power as the frequency decreases. In the embodiments presented herein, the antenna does not need to be driven at a resonant frequency. The resonant frequency presented by the combination of the inductance of the antenna 148 and any parasitic capacitance is typically well above the highest frequency of the transmission range, such as 45 KHz. In one example, the resonant frequency may be in the megahertz range.

[0053] In one embodiment of a wideband transmitter, the transmitted frequency group may range from SB3 to SB10, corresponding to a wideband frequency range of 9 KHz to 45 KHz. In the context of a wideband transmitter, no frequency restriction is required for any of these sub-bands (see, eg, Table 2).

[0054] Based on the above, the present application can provide a broadband transmitter with a single antenna, and the antenna is driven in such a way over a wide frequency band by using a single driving signal waveform or a lookup table in combination with a multiplier value, that is, the broadband transmitter can maintain a constant or controlled power consumption at least to an approximate value, when the power consumption shows a large change on the same frequency band. The power consumption variation over the broadband can be limited to an acceptable low level within the range of 9KHz to 45KHz. In this way, the applicant can provide a broadband transmitter that operates over a wide frequency range and has power consumption regulation and control functions that have not been seen so far. In the past, underground operations were performed at different frequencies for depth and positioning data, which usually required the purchase of a transmitter dedicated to each frequency of interest. Since a single broadband transmitter can replace multiple prior art transmitters, the knowledge disclosed herein can lead to significant cost savings. In this regard, the teachings of this article are also applicable to such a transmitter, which transmits depth frequencies or frequency modulations at discrete frequencies and transmits data signals at different frequencies, and the different frequencies are modulated in any appropriate manner (for example, using BPSK, QPSK or Manchester encoding).

[0055] As described above, applicants have recognized that it is beneficial to transmit depth frequencies or tones at relatively low or ultra-low frequencies (e.g., 1 KHz or lower) and transmit signal frequencies at one or more higher frequencies (e.g., in a range extending upward from 1 KHz or higher, such as above 4.5 KHz). In one embodiment, the transmitter 130 includes a mode that may be referred to as "rebar" or passive interference to reduce the effects of passive interference while maintaining data throughput at the data frequency. In this regard, in the absence of disclosure herein, low depth tone frequencies avoid passive interference sources such as rebar, but there is a risk of exposure to additional low-frequency active interference, while higher data frequencies are associated with higher data throughput based on the Nyquist rate. Because the presence of passive interference (e.g., rebar) distorts, weakens, and deforms the electromagnetic locating field of the transmitter, these negative effects may result in difficulty in accurately locating the location of the underground transmitter and inaccurate depth readings based on the signal strength of the locating signal, where the location of the underground transmitter depends on the shape of the locating field. For example, a location on the ground indicated as being directly above the transmitter may deviate from its actual location. In another example, when passing under rebar, a spike may occur in the transmitter of the displayed underground tool in response to signal attenuation caused by the rebar. It is beneficial to use a relatively low frequency for the depth signal in order to avoid these effects. To date, the transmission of the depth signal at a low frequency (e.g., below 1 KHz) proposed herein has been considered an insurmountable technical challenge for the prior art because of the view that ultra-low depth frequencies, such as those described above, would cause too much active interference to be practical. The present application distinguishes the cognitive limitations of the prior art from a hitherto undiscovered combination of features.

[0056] The present application allows the transmission of depth tones spaced apart from the modulated data frequency by an amount not previously mentioned, particularly when a single antenna is used to transmit both. For example, as will be described shortly below, the depth tones may be transmitted at a frequency of 1 KHz or less.

[0057] Now turn your attention to Figure 5c . Figure 5c4 is a schematic diagram of a series of transmitter frequency bands for an embodiment of the rebar mode, which are generally indicated by the reference numeral 420. Note that all frequency values ​​in the figure are in KHz. This embodiment also includes the transmitter frequency bands BT2-BT3 described previously, which are listed in Table 2 and repeated in Table 3. In this embodiment, a set of rebar frequency bands 424 includes a rebar low frequency band RBL extending from about 330 Hz to 400 Hz, a rebar middle frequency band RBM extending from about 405 Hz to 575 Hz, and a rebar high frequency band RBH extending from about 580 Hz to 750 Hz. Note that the number of rebar frequency bands and their endpoints can be varied in any suitable manner. For example, RBH can include an upper limit of 1 KHz or some other value between 1 KHz and the lower limit of BT2 at 4.5 KHz (e.g., 1.5 kHz). In another example, RBL can include a lower limit close to the power line frequency. In another example, an ultra-low frequency band can be added below RBL, and RBL can have a lower limit close to the power line frequency. In another example, an additional frequency band may be inserted between RBH and BT2. Likewise, as long as a multiplier value is specified for any potential transmit frequency that may be selected, there is no need to specify a multiplier for each frequency band.

[0058] The rebar frequency bands 424 are listed in Table 3. The last column of Table 3 includes a multiplier table 410, which is one embodiment that replaces the multiplier table 376 of Table 2 above when operating in the rebar mode. The multiplier table can vary in complex ways based on various factors, as shown in multiplier table 410, which is developed empirically. Figure 5c A sine lookup table is schematically shown as being affected by multiplication table 410, wherein waveforms 412a-412c correspond to RBL, RBM, and RBH, respectively. Waveforms 414a-414c correspond to SB2-SB4, respectively.

[0059] Table 3: Rebar pattern Transmitter frequency band Frequency band range Subband number Subband frequency range Multiplication Table 410 RBL 330 Hz to 400 Hz n / a n / a 0.34 RBM 405 Hz to 575 Hz n / a n / a 0.39 RBH 580 Hz to 750 Hz n / a n / a 0.47 BT2 4.5 KHz to 9 KHz SB2 4.5 KHz to 9 KHz 0.45 BT3 9 KHz to 18 KHz SB3 9 KHz to 13.5 KHz 0.55 BT3 9 KHz to 18 KHz SB4 13.5 KHz to 18 KHz 0.63 Table 4 shows example frequencies selected based on noise scanning when operating the transmitter in rebar mode. Note that data frequencies S0-S15 are all selected from SB4, but this is not required. In this regard, it is possible to select at least Figure 5cSB2-SB4 of the transmitter. It should be noted that the frequencies in SB2-SB4 generally provide a good transmission range and a relatively high data throughput or bandwidth. In this regard, one of the multiple sub-bands can be selected based on the average noise per sub-band learned during a noise scan, either manually or automatically or some combination thereof. At the same time, the depth frequency of 345 Hz provides a significant degree of immunity to passive interference (e.g., passive interference generated by steel bars). Considering the multiplier table 410 of Table 3, the multiplier can be set to 1.0 for the highest frequency or sub-band transmitted by a given embodiment of the transmitter. For example, the remaining entries in the multiplier table can be set to provide a constant power consumption based on the power allocated between the depth signal and the data signal or based on what the applicant has disclosed below. In one embodiment, the value of the multiplier table in the normal mode or steel bar mode can be determined empirically, such as while adjusting the transmission power of the depth signal relative to the data signal, observing the total power consumption of the transmitter so that it does not exceed the maximum power threshold. This empirical process may be best performed in an area of ​​low active interference. As will be discussed further below, specific embodiments may also consider the acceptance range of the depth signal relative to the data signal.

[0060] Table 4: Examples of selected frequencies for reinforcement patterns instruct Frequency (Hz) Depth signal 345 S0 14,740 S1 14,850 S2 15,085 S3 15,210 S4 16,500 S5 16,770 S6 16,695 S7 17,105 S8 17,190 S9 17,225 S10 17,240 S11 17,335 S12 17,445 S13 17,560 S14 17,680 S15 17,995 For comparison purposes, Table 5 lists the frequency selections for the normal mode, where the depth signal frequency is above 1 KHz.

[0061] Table 5: Example of selected frequencies for normal mode instruct Frequency (Hz) Depth signal 40,675 S0 40,740 S1 40,850 S2 41,085 S3 41,210 S4 41,500 S5 41,825 S6 42,235 S7 42,400 S8 42,700 S9 42,845 S10 43,205 S11 43,420 S12 43,665 S13 43,825 S14 44,360 S15 44,635 The selected frequencies in Table 5 are selected from subband 10. Applicants recognize that the presence of active interference detected in the noise scan forms the basis for these frequency selections, and that the presence of active interference does not affect the problems caused by passive interference. In this regard, attempting to use the depth signal frequencies of Table 5 may prove to be unfeasible, requiring switching to a reinforcement mode that uses a much lower frequency for the depth signal, such as 345 Hz as shown in Table 4. In another embodiment, the depth frequency and data symbol frequency selection in normal mode can be restricted to the same frequency range as the data symbol selection in reinforcement mode (from SB-2 to SB-4 in the example of Table 3). Note that in such an embodiment, the reception range of the data frequency at a given transmit power in normal mode can be at least slightly improved compared to the data signal reception range in reinforcement mode, at least due to the relatively low active interference in normal mode as a result of front-end filtering, but this remains to be discussed.

[0062] The transmitter and related components according to the present application have been described in detail above, and now the details about the transmission of the data signal 122 will be disclosed. Specifically, the M(ary) frequency shift keying method is used so that a plurality of different symbols can be streamed to form the data signal 122. In the reinforcement mode, the data symbol frequency can be selected in BT2 and / or BT3 to form the data signal 122, and based on the noise scanning to be described, a set of reinforcement frequency bands 424 (see Figure 5c ) selects a depth frequency of 120. In normal mode or reinforced mode, the data signal can be used to transmit a multi-bit symbol stream. Figure 4 The synthesizer 300 used, at least in part, facilitates the ability to transmit a multi-bit symbol stream. Specifically, a multi-bit data symbol stream can be provided to the symbol channel frequency control 340 at the data symbol stream input 374. In this way, data symbols corresponding to various different frequencies can be assigned to the data symbol stream, each different symbol corresponding to a different frequency. In one embodiment, the data symbols of the symbol stream can correspond to 16 symbols (4 bits), but any suitable number of symbols can be used based on the desired data throughput. Figure 4 An output 390 based on 16 symbols S0-S15 is shown, where S0 corresponds to the lowest frequency and each successive higher numbered symbol corresponds to a relatively higher frequency, but this is not required and the mapping or assignment of symbols to frequencies can be performed in any suitable manner. Thus, the output 390 corresponds to the example input symbol stream of S2, S12, S2, S15, S0 and S10 at the input 374.

[0063] Based on the foregoing, the applicant believes that the system 10 can provide a degree of active noise immunity and passive interference immunity that has not been seen heretofore in performing underground operations (such as horizontal directional drilling and related pullback or back-reaming operations). Relevant considerations and further details will be provided in the context of the discussion of the device 20, which receives the depth signal and the data signal and can also help determine the depth signal frequency and the symbol frequency to be used by the transmitter. It should be understood that the symbol frequency ordering given in Table 4 is not required. In Table 5, the depth signal frequency can be located between the symbol frequencies. Based on the use of a separate signal for the purpose of generating a depth signal, the depth signal can be located in a sub-band different from the symbol frequency. In addition, the symbol frequency can be reordered or rearranged in any appropriate manner. With respect to prioritizing the frequency selection to a single sub-band, it should be understood that embodiments of the broadband transmitter can be configured to operate in a manner that mimics the operation of a transmitter that is limited to sub-band-based operation. For example, the selected frequency in the broadband transmitter can be limited or constrained to a single sub-band, even if the broadband transmitter is able to transmit over a wide range of sub-bands.

[0064] Figure 6ais a graph of the power spectral density of noise obtained at high resolution, generally indicated by reference numeral 500, corresponding to actual physical locations using a 50 Hz power line frequency. Signal levels are shown on the vertical axis and frequencies are shown on the horizontal axis. The frequency range of 0 to 45 KHz corresponds to the frequency range covered by the range of transmitters described in accordance with the present application. Transmitter sub-bands SB1-SB10 are also shown in the figure. It is noteworthy that sub-band 1 is very noisy compared to the noise seen in most of the higher frequency sub-bands. In this regard, the present application proposes that a person of ordinary skill in the art would at least therefore reject the idea of ​​using depth signals with frequencies below 1 KHz or 1.5 KHz, which will be discussed further. However, the present application has revealed a comprehensive improvement that provides accurate positioning of depth signals at low active noise frequencies, which can even be below 1 KHz.

[0065] Although Figure 6a The spectral scan of shows spectral information at essentially a single location, but it should be understood that frequency information can be collected in a cumulative manner. For example, a spectral scan can be performed while an operator walks along a planned borepath with the device 20 while the device characterizes the noise environment. In this way, Figure 6a The frequency map can be considered to represent the noise environment along the entire planned drilling path, where subsequent frequency selection is based on the noise environment characterized for the entire length of the planned drilling path, while still utilizing the frequency selection techniques disclosed herein.

[0066] Figure 6b One embodiment of a screen shot of a display 36 is shown including a bar graph display showing the average noise for each subband operating in normal mode, wherein subband SB-10 is highlighted, for example using shading and / or color or in some other appropriate manner, indicating that SB-10 has been automatically selected. In another embodiment, the locator may make automatic recommendations based on the average noise for each subband in combination with other statistical values. Any appropriate statistical values ​​may be used including, for example, standard deviation, minimum noise, and peak noise. In yet another embodiment, more than one subband may be recommended, in which case the user may select between the recommended subbands. Multiple subbands may be recommended based on a limited amount of statistical variation between the subbands. For example, subbands 9 and 10 may be recommended based on a relatively limited difference between the two subbands, as shown in FIG. Figure 6bIn another example, multiple subbands may be recommended, for example, based on the fact that the average noise of the first subband is lower than the average noise of the second subband, while the peak noise of the first subband is higher than the peak noise of the second subband. In one embodiment where more than one subband is recommended, the system may be configured to enable a user to select one of such multiple recommended subbands for transmission. In another embodiment, a user may select multiple recommended subbands for transmission. In yet another embodiment, one or more of such multiple recommended subbands may be automatically selected for transmission. Figure 6a The information presented in is based on high resolution noise scans using 5 Hz increments, so a lot of noise information can be extracted from the data. For example, the standard deviation of the noise values ​​within each known value can be determined. Figure 6b The height of each bar in can be weighted by adding or subtracting some value based on one or more other statistics. For example, if the standard deviation of a given subband is high, meaning that the distribution of noise values ​​is relatively wider, then the height of the associated bar can be maintained or even increased by some amount. On the other hand, if the standard deviation of a given subband is low, meaning that the noise values ​​within that subband are relatively uniform, then the height of the associated bar can be reduced. Figure 6b . Similarly, the height of the bars in the bar graph can be weighted based on the peak noise, so that subbands with high peak noise can be increased in height by a certain amount. In any case, the weighting can be performed based on thresholds for individual statistical values. The weighting can be applied based on individual statistical values ​​or a combination of statistical values. The operator can accept the automatic selection of subbands by touching the automatic selection button 780 or by touching any subband he or she wishes to select. The operator can override the automatic selection, for example, based on which designated transmitters are currently available to perform underground operations. As another basis for presenting information to the operator, other statistical values ​​can be presented. For example, the upper horizontal line 781 (some of which are individually designated) shows the peak noise for each subband. The operator can choose to avoid displaying subbands with particularly high peak noise levels, even if the average noise of the subband is relatively low. To override the automatic selection, the operator can touch the manual selection button 782 and then touch the subband he / she wishes to select. In another embodiment, the display 36 on the locator can display a plot, a bar graph, or a selection from Figure 6a , so that the operator is then allowed to manually select one of the plurality of sub-bands, for example, by touching the sub-band on the display screen. In yet another embodiment, the locator 20 may allow the operator to initially input information about transmitters that may be used to automatically select a sub-band covered by one of the transmitters and exclude unusable sub-bands in a manner consistent with the teachings of U.S. Patent No. 8,729,901, which is owned by the same applicant as the present application and is incorporated herein by reference in its entirety. Figure 6b Unavailable subbands based on unavailable transmitters are shown using dashed lines. Conversely, solid lines represent available subbands. In this example, SB-1 and SB5-SB-7 are unavailable. In one embodiment, subbands can be excluded based on regulatory constraints. In this way, the portable device itself and the operator are not allowed to make frequency selections that would violate regulations in a particular jurisdiction. Such frequency restrictions can be predetermined by the manufacturer on a regional basis. In one embodiment, the portable device 20 or other components of the system (e.g., the drill rig 80) can be equipped with a GPS receiver that can establish the location of the underground operation and then look up local frequency requirements.

[0067] Still see Figure 6b , the display screen shown can remain "real time" at least until the frequency selection process is complete. That is, the average noise of each sub-band can be monitored and displayed in real time, either alone or weighted by other statistical parameters, for operator monitoring purposes. In this way, the operator can move the locator around while observing the average noise in the various sub-bands. For example, the operator can walk along a planned borehole path before starting drilling and monitor the noise along the borehole path. In this way, sub-bands that are particularly noisy at one or more locations along the borehole path can be avoided. If the operator so chooses, he / she can move the locator to a different location, for example along the borehole path, and initiate a rescan of the noise across the bandwidth by selecting the rescan button 784. As described above, the noise environment can be characterized based on reception using one or more antennas. The operator can use button 786 to change the receive mode. For example, in one receive mode, reception along a single axis (e.g., the X-axis) can be presented. Figure 6b In another receive mode, a bar graph may be presented based on the sum of vectors generated from three orthogonal receive axes. Button 786 may also be used to initiate a reinforcement mode and / or to switch between reinforcement mode and normal mode. In this regard, the appearance of display 36 may be changed, as will be described at an appropriate location below. Once the operator changes the receive mode, rescan button 784 may initiate a new noise scan and present noise values ​​based on the selected receive mode. The operator may switch between the various noise scan modes at will. In one embodiment, a bar graph may be presented based on the sum of vectors generated from three orthogonal receive axes. Figure 6b The noise scan underlying the display of can be a high resolution scan. In conjunction with the execution of the noise scan, a plurality of optimized low noise frequencies can be automatically selected based on the number of symbol frequencies required. For example, 16 symbol frequencies and 1 depth frequency can be selected for each subband. In one embodiment, Figure 6bDuring the presentation of active noise on the screen of FIG. 78 , the noise of each sub-band can be represented as the average of the noise values ​​measured at each selected frequency within each sub-band. Note that selection of the rescan button 784 will result in a new or updated selection of frequencies within each sub-band. The locator 20 can be configured to, for example, Figure 9a Multiple sets of frequency selections associated with different measurement locations are stored in the memory 714 of the . Thus, the frequency selection is optimized for each measurement location so that different selections can be used at different times during operation. The term "optimized" is intended to mean that the selected frequencies are selected with the goal of avoiding interference based on one or more statistical parameters (e.g., mean noise, standard deviation, and peak noise). Figure 3 The external communication connection 174 can transmit multiple sets of frequency selections to the transmitter above the ground. During underground operation, the underground transmitter can be commanded to switch to a different set of frequency selections in any suitable manner. For example, the switch between rebar mode and normal mode can be commanded based on a predetermined rolling sequence of the drill string or by transmitting an electromagnetic signal received by the transmitter (in this case, the transmitter 130 is configured as a transceiver) from above the ground. Some embodiments can use the drill string as an electrical conductor or can include a known metal wire pipe arrangement so that data can be transmitted between the underground transmitter / transceiver and the drill rig. For example, the drill rig can send a command via the borehole to switch between rebar mode and normal mode. In one embodiment, based on the orientation of the transmitter at startup (when the battery has been installed), it is initially determined to operate in rebar mode or normal mode. For example, one end of the transmitter can be oriented upward to determine operation in normal mode, while the end can be oriented downward to determine operation in rebar mode.

[0068] Figure 6cOne embodiment of a screen shot of a display 36 including a bar graph showing noise measurement results operating in rebar mode is shown, wherein sub-band SB-4 is highlighted, for example using shading and / or color or in some other appropriate manner, indicating that SB-4 has been automatically selected for data transmission. Together, bars 790, 792, 794 are associated with rebar bands RBL, RBM, and RBH, respectively. In this case, each column height of the rebar band shows the measured active noise of the lowest noise frequency, which may be referred to as the potential depth frequency, which may be detected by a scan in each rebar band, while the columns from SB-2 to SB-4 may indicate the average of the data symbol frequencies in each sub-band, as described above. The automatic selection or recommendation of the lowest noise frequency in the rebar band may be indicated by cross-hatching or other visually appropriate manner, in this case RBM, but this is not required. The operator may select, override, or change the selected rebar frequency by touching the band column, for example. It should be understood that a noise scan over the entire bandwidth may be used to generate Figure 6b and Figure 6c of the screen content, but this is not required. Then, for the noise scan, Figure 6c The display can present the real-time noise indication of each steel bar frequency band, so that the operator can walk along the planned drilling path and monitor the corresponding noise change. In another embodiment, multiple depth frequencies can be emitted. For example, each steel bar frequency band RBL, RBM and RBH can be emitted at a series of intervals for ground reception. It should be understood that such multiple frequencies can be selected in normal mode and emitted in a similar manner. The reception of multiple depth frequencies will be discussed in the appropriate position below.

[0069] Figure 7 It is from Figure 6a A further enlarged view of subband 10 of FIG. 1 is generally indicated by reference numeral 550 and is shown here to illustrate the selection of a depth frequency and sixteen symbol frequencies S0-S15 within the subband for normal mode. Note that based on the available frequency range for data transmission ( Figure 5c The symbol frequencies for data transmission in the rebar mode can be selected in a similar manner by scanning the noise of the sub-bands SB-2 to SB-4 in the rebar mode, while the rebar depth signal frequencies are selected from the rebar frequency band group 424, respectively, as shown in FIG. Figure 6c As shown. Figure 7, each selected frequency is represented by an arrow. Different frequencies have been selected, for example, based on their correspondence with low noise points in the noise map. Based on manually and / or automatically selected frequencies (e.g., S0-S15), the system 10 proposed by the applicant can provide a heretofore unprecedented level of noise immunity with respect to performing underground operations (e.g., horizontal directional drilling and related pullback or backreaming operations). With respect to immunity to passive interference, the reinforcement pattern disclosed herein provides heretofore unprecedented characteristics. Relevant reasons and further details will be provided in the context of the discussion of the device, which receives the depth signal and the data signal and can help determine the depth signal frequency and symbol frequency to be used by the transmitter.

[0070] Figure 8 A flow chart for operating an embodiment of a transmitter according to the present application is shown and is generally indicated by reference numeral 600. Note that for the purposes of this discussion, it will be assumed that a depth frequency and a frequency associated with symbols S0-S15 have been selected for each of the normal mode and the rebar mode. These frequency selections may be stored in any suitable location, such as in Figure 3 The method begins at step 602 and proceeds to step 604 to select normal mode or reinforced mode in any suitable manner. At step 606, the depth multiplier is read. At step 608, the transmitter reads the depth multiplier from, for example, the incremental lookup table 370 (see FIG. 14 ) as part of the operation of the depth channel frequency control 338. Figure 4 ). When using a single depth channel waveform lookup table (e.g. Figure 4 In an embodiment where multiple depth waveform lookup tables are used (e.g., table 326 in FIG. 1 ), the depth channel phase accumulator 330 can always address the single waveform lookup table in conjunction with retrieving the appropriate multiplier value from a multiplier table (e.g., multiplier table 376 or 410). On the other hand, in an embodiment where multiple depth waveform lookup tables are used, step 609 can also identify the correct waveform lookup table so that the depth channel phase accumulator 330 addresses the appropriate depth channel lookup table waveform based on the frequency. In step 610, the depth channel phase accumulator 330 begins counting based on the depth frequency increment, thereby (subject to the multiplier value) causing the lookup table 326 and the depth channel PWM generator 350 to begin continuously generating the depth channel frequency to transmit the depth signal 120 at that frequency. In step 614, the CPU 200 reads the sensor information via the multiplexer 154 to collect the sensor data to be transmitted. In step 618, the CPU combines the sensor data into a symbol stream that can call a packet structure to be described. The symbol stream is provided as a data stream symbol input 374 to the CPU 200. Figure 4619, the depth signal frequency multiplier may be read. In step 620, the symbol channel frequency control may utilize the lookup table 326 to determine the appropriate frequency for the current symbol to be transmitted and the multiplier value (e.g., multiplier table 376 or 410). On the other hand, in an embodiment using multiple symbol waveform lookup tables, step 620 may also identify the correct waveform lookup table so that the symbol channel phase accumulator 334 addresses the appropriate symbol channel lookup table waveform. It should be understood that for the transmission of a given symbol stream, it may be necessary for step 620 to switch the multiplier value from one symbol to the next symbol based on frequency on a symbol-by-symbol basis. In step 624, the current symbol is transmitted. Step 626 checks the availability of another symbol to be transmitted. If the symbol is available, the operation returns to step 620 so that the next symbol can repeat the process. On the other hand, if the next symbol is not yet ready, the operation may be directed to step 630, which responds to a request to switch from one mode to another mode between the normal mode and the reinforcement mode. The request may be provided in any suitable manner, such as based on a rolling directional sequence, data transmission via the drill string, and wireless communication. If there is no request, the operation may return to step 610 and the depth signal may continue to be transmitted. The sensor data may then be read again at step 614 and the process may continue from there. On the other hand, if there is a request to switch frequency bands, the operation may return to step 606 and the process may continue from there. It should be understood that the data signal 122 is most often transmitted simultaneously with the depth signal 120 on a substantially continuous basis.

[0071] The embodiments of the transmitter 130 have been described in detail above. In order to describe additional details about the device 20, which may be referred to as a transmitter or a receiver, the following will now be described in conjunction with the embodiment of the transmitter 130. Figure 1 Direct your attention to Figures 9a to 9c . Figure 9a A block diagram of the device 20 is shown. The latter comprises a battery 700 which feeds a power supply 704 which provides appropriate power, indicated as V+, to all components of the device. The electronic part 32 comprises a processor 710 which interfaces with a memory 714. A telemetry part 720 is controlled by the processor and is coupled to the antenna 40 for bidirectional communication via the signal 44. In some embodiments, the telemetry link may be a one-way communication from the device 20 to the drilling rig, in which case the transceiver 202 need only have a receiver function. The external communication means 722 uses an external communication connection 174 (see transmitter) to communicate with the drill rig. Figure 3) to communicate externally with the transmitter. As described above, such communication need not be transmitted underground, but can be performed when the transmitter is above the ground (e.g., at a location adjacent to the device 20). External communication can be implemented in any suitable manner, including but not limited to IrDA, NFC, Wi-Fi, Zigbee, or Bluetooth. The broadband dual-mode front end 730 is configured to receive the depth signal 120 and the data signal 122 using the X, Y, and Z antennas that constitute the antenna cluster 26, which are used to measure the three orthogonal components of the object signal and for noise measurement along these axes, as will be described. Additional details about the implementation of the antenna cluster will be provided below at appropriate locations. Each of the X, Y, and Z antennas is interfaced to low noise amplifiers (LNAs) 734a, 734b, and 734c that can be configured identically. The amplified output of each LNA can be provided to a switchable filter section 738a, 738b, 738c, which can be configured identically and can be collectively referred to as a filter section 738. Each filter section includes two bandpass filters 740a and 740b, which are used to present a low frequency roll-off or corner and a high frequency roll-off or corner. Filter 740a can be referred to as a normal mode filter, while filter 740b can be referred to as a steel bar mode filter. Although filters 740a and 740b are shown as separate functional blocks, it should be understood that the filters can be implemented in any suitable manner. As a non-limiting example, each filter can be implemented as a series of RC high-pass filters and low-pass filters distributed throughout the signal chain. Figure 9b The curve 742 schematically shows the normalized frequency response of the normal mode filter 740a. In one embodiment of the normal mode filter, the two high pass filters can each be set at a low corner frequency of about 4KHz, and the four low pass filters can be set at a high corner frequency of about 90KHz. This embodiment produces a relatively flat frequency response, which has a lower corner frequency 742a at about 10KHz and a high corner frequency at about 50KHz. The roll-off below 10KHz is about 40dB per decade attenuation, while the roll-off above 50KHz is about 80dB per decade attenuation. Fig.9cSchematically illustrated is an embodiment of the normalized frequency response of the steel bar mode filter 740c, which is indicated by reference numeral 744. As shown, the high corner frequency 743b can be unchanged, but this is not required. On the other hand, the low corner frequency 745 can be moved down to, for example, about 180Hz at a roll-off of about 3dB. In this way, there is almost no signal attenuation at 300Hz. It should be understood that the low-end response of the filters 740a and 740b can be established to take into account the fundamental and low-order power line harmonics, which can be very strong, especially in the case of the steel bar mode filter. The filter switching line 747 is shown with a dotted line, which extends from the CPU 710 to each filter of the filter section 738. Therefore, the CPU 710 can control the filter selection in the normal mode and the steel bar mode. The amplifiers 750a-750c can follow each of the filters 738a-738c with sufficient gain to drive each of the analog-to-digital converters A / D 754a-754c. Each A / D 754 provides an output to the CPU 710. In one embodiment, the apparatus 20 may be configured to receive the symbol stream in a manner that suppresses power line harmonic frequencies because there is virtually no energy in the symbol stream at the power line harmonics. For example, the received signal may be processed so that the receiver response matches Figure 7 553 of the symbol spectrum. In particular, by integrating the received symbol stream over a time period corresponding to the duration or period of each symbol, the spectral response of the receiver can be matched to the spectral characteristics of the transmitter. In this way, the receiver frequency response matches the transmitter's response about null reception points present at the power line harmonic frequencies. Thus, the receiver suppresses or ignores energy at the harmonic frequencies while sweeping up spectral energy associated with the symbols. The receiver may employ any suitable conditioning process that provides periodic nulls, including but not limited to a discrete Fourier transform (DFT).

[0072] See also Figure 9b and Fig.9c , given that Figure 6a With the spectral plot of and the points made in the previous discussion regarding high active noise below the ultra-low depth frequency range proposed by the applicant (e.g., below 1 KHz), it is worth comparing the response 742 of the normal mode filter and the response 744 of the rebar mode filter. In this regard, the low frequency corner 743a of the normal mode filter is located at approximately 4 KHz, while the low frequency corner 745 of the rebar mode filter is located at no greater than approximately 185 Hz. While reducing the low frequency corner of the rebar mode filter enables depth signals to be detected at extremely low depth signal frequencies of at least as low as 300 Hz or as low as appropriate power line frequencies, it should be understood that it also introduces serious technical challenges. In particular and as Figure 6aAs shown, the rebar mode filter tolerates a large amount of noise between 180 Hz (or even lower) and 4 KHz, which would normally be rejected by the normal mode filter. For example, such noise may contain very strong power line harmonics. It is submitted that tolerating all of this noise is counter-intuitive to one of ordinary skill in the art and may be considered to potentially render a portable device unusable for receiving such low depth signals as well as introducing additional difficulties in receiving higher frequencies. However, the applicant recognizes that the combined teachings herein provide for allowing such additional noise to enable reception of extremely low frequency depth signals while providing the ability to locate the depth signal to a reasonable approximation at an accurate frequency in the rebar frequency band where noise may be absent. In this way, the depth signal can be detected while ensuring immunity to generally high ambient noise levels below 1 KHz or other suitable limits (e.g., 1.5 KHz). The applicant is not aware of a combination of these features existing in the prior art.

[0073] See also Figure 9a , embodiments of the locator 20 have been described in detail above, it should be understood that the locator can be configured to perform noise measurements and analysis in order to select a transmitter for transmitting the depth signal and the data signal, and to determine the frequency associated with each of these signals. Of course, when a broadband transmitter is used, frequency band selection may not be required. The antenna 26 (e.g., Figure 9a Noise measurements may be determined for each orthogonal axis of the locator (e.g., the X, Y, and Z antennas shown). These individual noise components may be used to determine a three-dimensional noise value, for example based on a vector sum of the three antenna components. The vector sum may be useful because the noise reading at a given location will be substantially constant when the orientation of the locator changes. On the other hand, a display of noise readings obtained from a single axis will exhibit changes at a given location when the orientation of the locator changes. By allowing noise to be monitored along a single antenna axis (e.g., the X axis), an operator may identify which particular axis along the borehole path may be problematic in terms of interference. The noise value may be determined in any suitable manner, such as based on a Fast Fourier Transform (FFT). In one embodiment, a noise scan may be generated from each axis for comparison purposes. For example, for data recovery purposes, different treatments may be used for axes that exhibit relatively higher noise than other axes.

[0074] Now turn your attention to Fig.10a , Fig.10a Is from Figure 6a8 is an expanded view of a sub-band 6 of the subsurface detector, which is generally indicated by the reference numeral 800. For the purposes of this discussion, it will be assumed that the SB-6 is available and has been automatically selected or selected by the operator for use during underground operations. Note that according to these descriptions, symbol / data frequency selection can be made for any sub-band. Operation in normal mode is assumed at least initially. After the sub-band is selected, the frequencies of the depth signal 120 and the data signal 122 can be determined. In one embodiment, the frequencies can be determined by, for example, the manufacturer or based on a previous noise scan, as described above. In another embodiment, the display 36 can be used to display the sub-band in any suitable form. Fig.10a The spectrum diagram is presented to the operator of the locator so that the operator can make frequency selection. Fig.10b One embodiment of a screen shot is shown showing the display 36 showing the SB-6, which is still presented in normal mode. It should be understood that the locator can provide a zoom function using the zoom in button 802 and the zoom out button 804 on the display 36, so that the operator can expand the horizontal range of the spectrum display to provide detailed frequency selection. Generally, the operator can select frequencies that correspond to low noise points on the displayed spectrum. These selections can be rounded to reflect the frequency resolution of the transmitter to be used. As described above, as a non-limiting example, a transmitter according to an embodiment of the present application can have a frequency resolution of 5 Hz. Fig.10a 21 low noise points are identified above, represented as rises (a)-(u). In an embodiment using one depth frequency for the depth signal 120 and 16 symbol frequencies, 17 of the 21 frequencies may be used. As described above, the depth frequency may be mixed with the symbol frequency and located anywhere within the sub-band, at either end of the sub-band or even in a different sub-band. In one example, the depth frequency may be selected as the lowest noise point among the determined frequencies; in this example, frequency (j). In another embodiment, a frequency may be automatically selected or reselected by the locator 20, for example, in response to an operator selecting an "auto select" button 806 on the display 36. In one embodiment, the processor 710 may check Figure 6a The frequency spectrum is then sorted to identify the lowest noise point until a suitable number of symbol frequencies are available. In other embodiments, the processor may perform the selection process based on any suitable method. For example, the lowest noise frequency may be selected in conjunction with maintaining a minimum spacing between adjacent frequencies. For the rebar pattern, frequency selection may include the selection of data symbols that are Fig.10b The display of the 420 bands may be substantially the same, with additional depth frequency selections, such as in the rebar band group 424, which may be based on, for example, Figure 6c The display of the steel band 424 shown or the display of the noise scan results of the steel band group or a display similar to or based on Fig.10bIn this way, the operator has great flexibility in selecting the depth frequency in the reinforcement pattern.

[0075] Still see Fig.10b , frequencies may be added by, for example, touching the add frequency button 808 and then touching the spectrum graph. Frequencies may be deleted by, for example, touching the delete frequency button 810 and then touching the frequency to be deleted. Frequencies may be moved by, for example, touching the move frequency button 812 and then touching and dragging the frequency to be moved. The selected subband may be changed by touching the change subband button 814. As will be further described below, frequency selection is not limited to identifying low noise points, but may also take into account high noise points or areas of the spectrum scan.

[0076] Fig.11 yes Fig.10a A further expanded view of the frequency spectrum region from 24 KHz to 25 KHz is generally indicated by reference numeral 820 and is shown here for the purpose of describing further details of frequency selection. In addition to identifying low noise points, as described with respect to Fig.10a As described, the processor 710 may apply what may be referred to as a "keep-out region." The latter will exclude any identified low noise frequencies having noise peaks within a selected frequency window 822 centered about the low noise frequency. Noise is identified based on, for example, an amplitude exceeding a threshold 824, which is based on an average noise value for a sub-band and / or a noise value associated with a nearby low noise point. In one embodiment, the width of the frequency window may be approximately 60 Hz (+ / - 30 Hz) and the threshold may be at or above the associated low noise point by 10 dB or more. Based on the use of such a frequency window, frequencies (b) and (e) may be excluded due to their proximity to peaks 826 and 830, respectively. In the event that more frequencies are needed, the processor 710 may re-examine in order to determine a new set of candidate frequencies. Fig.11 In the Rebar frequency band group, the Rebar frequency window can have a different width than the frequency window in normal mode. For example, the Rebar frequency window can be narrower because the noise sweep can be performed in small increments (e.g. 5Kz).

[0077] Fig.12a900 is a flow chart illustrating an embodiment of a method for performing spectrum scanning and frequency assignment in subsequent operation of the locator 20 in normal mode according to the present application. The method begins at step 904 and proceeds to step 908, where a scan of the entire spectrum, for example from 0 Hz to 45 KHz for the present embodiment, is performed, but the scan may use any suitable frequency range. The scan may be a high frequency scan, for example using a resolution of 5 Hz, as described above. In another embodiment, an initial, lower resolution scan may be used so that the resolution is just sufficient to establish an average noise value for each sub-band. If the sub-band selection process relies on a lower resolution spectrum scan, a high resolution spectrum scan may then be performed as part of the frequency scanning process, as described below. When a broadband transmitter is used for underground operation, a single high resolution scan may be used for frequency selection. At step 910, the average noise value for each sub-band is determined. At step 914, a sub-band may be recommended based on the average noise value. Typically, the sub-band with the lowest average noise value may be selected, but other embodiments may use different recommendation schemes and / or automatic selection. For example, the sub-band with the lowest noise peak may be recommended. In another example, as described above, more than one sub-band may be recommended. At step 918, user input may be requested on the display 36, where the user may accept the recommended sub-band or select a different sub-band. For example, the user may select a different sub-band based on knowledge of the transmitters that may be used to perform underground operations. As described above, this information may be used as an initial input so that the method 900 excludes sub-bands that are not covered by one or more transmitters that are currently available. Once a sub-band has been selected, the method proceeds to step 920, where the sub-band frequencies are determined. In one embodiment, the sub-band frequencies may be pre-determined and stored in the locator's memory 714 or in the transmitter's memory 218. In another embodiment, as discussed above, the sub-band frequencies may be determined on-the-fly by the operator by presenting the sub-bands on the display 36. In another embodiment, the sub-band frequencies may be determined based on information related to the locator's memory 714 or in the transmitter's memory 218. Figure 10a-10b and Fig.11As discussed above, sub-band frequencies are automatically determined with or without applying a keep-out window as applied in step 924. In the case of using a broadband transmitter to perform underground operations, steps 910 and 914 are not required because the entire transmission bandwidth is available for frequency selection without limiting the frequencies to any particular one or more sub-bands, and step 920 can allocate frequencies across the entire transmission bandwidth. Thus, transmission frequencies can be automatically selected across the entire available bandwidth and / or customized by the user based on a high-resolution noise scan without requiring frequency allocation restrictions based on sub-bands. It should be understood that embodiments of broadband transmitters can be configured to operate using sub-bands in the same manner as sub-band limited transmitters, for example based on operator preferences, where frequency allocations can be limited to one or more sub-bands in a sub-band limited transmitter, although this is not required. In step 928, it is determined whether a sufficient number of frequencies have been identified. If not, the operation returns to step 920 to identify additional frequencies. If a sufficient number of frequencies have been identified, the operation proceeds to step 930, where frequencies for the depth signal 120 and the data signal 122 are recommended. This latter step may be optional in a fully automated implementation. In step 934, information may be presented on the display 36 to collect user input, such as approving the frequency selection or changing the frequency selection. For example, the user may prefer to move the depth frequency to a different location within the sub-band or to an entirely different sub-band. Of course, in a broadband transmitter implementation, no restrictions need be imposed on limiting the frequency selection to a particular band and / or sub-band. In step 938, the locator's external communication device 722 and the transmitter's external communication link 174 (see FIG. 14 ) may be used to communicate with the locator. Figure 3 ), the frequency may be transmitted to the transmitter 130. Then, at step 940, normal mode operation may be entered during the underground operation process.

[0078] In one embodiment of method 900, the number of selected frequencies can be based on the noise environment. For example, whether or not sub-band limited, if the noise scan shows a low noise environment, relatively more frequencies can be selected. In this case, 32 or more symbol frequencies can be used instead of 16 symbol frequencies. If the noise scan shows a high noise environment, relatively fewer frequencies, such as 4 or 8 symbol frequencies, can be used instead of 16 frequencies. In general, using relatively fewer frequencies can help avoid variable noise sources in high interference environments. On the other hand, using a greater number of symbol frequencies can increase data throughput.

[0079] Figure 12b944. The method begins at step 946 and proceeds to step 948, where a scan of the entire frequency spectrum, for example, from 0 Hz to 45 KHz for the present embodiment, may be performed, although the scan may use any suitable frequency range. For example, based on Figure 5c , the scan can be from about 0 Hz to 18 KHz. The scan can be a high frequency scan, for example with a resolution of 5 Hz, particularly for the reinforcement band group 424. A lower resolution can be used in order to select the symbol frequency, as described above. In step 950, the average noise value of each sub-band can be determined for the symbol frequency sub-band, and the scan frequency can be analyzed as a potential depth signal frequency for use. The sub-band for the data symbol can be recommended and / or selected based on any suitable statistical value (e.g., average noise value, minimum noise value, peak noise value and / or standard deviation value) in a manner consistent with the above description and in combination with recommending one or more depth signal frequencies. In step 954, user input can be requested on the display 36, where the user can accept the recommended sub-band or select a different sub-band for the data symbol. The user can also select, modify or confirm one or more potential depth signal frequencies. Note that in an embodiment where automatic frequency selection is performed for the user, user input is optional. Once the sub-band and depth signal frequency have been selected, the method proceeds to step 956, in which the sub-band frequency and depth frequency are set. In one embodiment, the sub-band frequencies and depth frequencies may be predetermined and stored in the locator's memory 714 or the transmitter's memory 218. In another embodiment, the sub-band frequencies and / or depth frequencies may be determined on the fly by the operator by presenting the sub-bands and / or rebar frequency bands on the display 36, as discussed above. Figure 10a-10b and Fig.11 Related discussion, sub-band frequencies and / or depth frequencies are automatically determined with or without the application of a rejection window as applied in step 958 and discussed above.

[0080] Note that, as described above, the determination and indication based on the sub-bands in step 950 is not required, because the frequencies do not need to be limited to any particular sub-band, and step 950 can allocate frequencies across the entire transmission bandwidth. Therefore, the transmission frequency can be automatically selected across the entire available bandwidth and / or customized by the user based on a high-resolution noise scan. It should be understood that embodiments of the wideband transmitter can be configured to operate using sub-bands in the same manner as a sub-band limited transmitter, for example, based on operator preferences, where the frequency allocation can be limited to one or more sub-bands in a sub-band limited transmitter, although this is not required. In step 960, it is determined whether a sufficient number of frequencies have been identified. If not, the operation returns to step 950 to identify additional frequencies. If a sufficient number of frequencies have been identified, the operation proceeds to step 962, where frequencies for the depth signal 120 and the data signal 122 are recommended. This latter step may be optional in a fully automatic embodiment. In step 964, information can be presented on the display 36 to collect user input, such as approving the frequency selection or changing the frequency selection. For example, the user may prefer to move the depth frequency to a different location within the rebar frequency band or to an entirely different rebar frequency band. Of course, in a broadband transmitter embodiment, no restrictions need be imposed on limiting the frequency selection to a particular frequency band and / or sub-band. Again, no user input is required in a fully automatic embodiment. In step 966, the locator's external communication device 722 and the transmitter's external communication link 174 (see FIG. 14 ) are used to communicate with the locator. Figure 3 ), the frequency may be transmitted to the transmitter 130. Then, at step 968, rebar mode operation may be entered during the underground operation process.

[0081] Now combine Figure 12b Turn your attention to Fig.12c . Fig.12c It shows Figure 12b A flow chart of one embodiment of a method for analyzing frequencies of a scan in a depth frequency band of step 950 is generally indicated by reference numeral 970. The method begins at step 972 and proceeds to step 974, where a comparison is made from Figure 5c The noise values ​​obtained in the noise scan of each of the reinforcement frequency bands RBL, RBM and RBH are used to identify at least the frequency exhibiting the lowest noise value in each of these reinforcement frequency bands at step 976. In this embodiment, the result is a set of three low noise potential depth signal frequencies. At step 978, the noise values ​​can be obtained based on, for example, Figure 6c The set of low noise frequencies may be displayed on a display of the display, and / or automatic selection of the lowest noise frequency from the set of frequencies may be performed. In step 980, the operation may return to Figure 12b Step 950.

[0082] Now combine Figure 12b Steering Fig.12d , Fig.12d It shows Figure 12b A flow chart of another embodiment of a method of analyzing scanned frequencies in a depth frequency band of step 950 is generally indicated by reference numeral 982. The method begins at step 983 and proceeds to step 984, where a plurality of noise values ​​obtained from a noise scan of the entire rebar noise frequency band or range are compared to a threshold noise value, which threshold noise value may be at least initially a low value, for reasons that will become apparent in the context of what will be discussed. At step 985, low noise frequencies that do not exceed the threshold are identified. At step 986, a test is performed to determine whether any frequencies are identified as a result of the low value of the noise threshold. If a frequency is identified, operation branches to step 987, where the depth signal frequency may be displayed, automatically selected, and / or confirmed as needed in collaboration with the operator. At step 988, operation returns to Figure 12b 950. On the other hand, if no frequency is identified at step 986 (because all scanned frequencies exhibit noise levels above the threshold noise level), the operation branches to step 990, where the operator can be queried to trigger a rescan of noise at least in the rebar frequency band. Note that decision 986 is not required. In this regard, any suitable response to excessive or severe active interference can be provided. For example, in another embodiment, an indication can be issued to the operator indicating that severe noise is present in the rebar frequency band. In this embodiment, if rescanning is selected, the operation proceeds to step 991 for rescanning and then returns to step 985. At step 990, if the user does not request a rescan, the operation can proceed to step 992, where the user is asked whether he would like to increase the noise threshold. If so, the noise threshold can be increased, for example, by a predetermined incremental value or the user can specify an increase value. The operation can then return to step 991 and continue execution from there. At step 992, if the user does not choose to increase the noise threshold, the operation may proceed to step 993, where the user is asked whether he or she wants to leave the reinforcement mode and enter the normal mode (assuming there is too much local active noise in the ambient operation). If the user chooses to return to the normal mode, the normal mode is entered at step 994, at which time, for example, the user may call Fig.12a On the other hand, at step 993, if the user does not choose to enter normal mode, then operation proceeds to step 995, which is not required but may involve selecting a depth signal frequency based on satisfying a different set of noise technical parameters. Operation then proceeds to step 987. An implementation of step 995 may be in Fig.12e As seen below, although it can be independent of Fig.12d Method 982 entry Fig.12e process.

[0083] See now Fig.12e , which shows Figure 12b Another embodiment of the method for analyzing the frequencies of a scan in a depth band of step 950 is generally indicated by the reference numeral 1000, or may be used as Fig.12d Note that method 1000 can be used as a primary implementation for identifying depth signal frequencies and / or as a further inspection process ( Fig.12d 995) to ensure that the identified frequency is as low as practical for use, as will be apparent from the description below. In this regard, it should be noted that immunity to passive interference generally increases with decreasing frequency, making it beneficial to employ the lowest practical frequency. The method begins at step 1004 and proceeds to step 1006, where the lowest noise frequency f(low) is found in the rebar frequency band based on a noise scan (e.g., scanning in increments of 5 Hz). At step 1008, although not required, an offset from the lower limit of the rebar frequency band may be determined. At step 1010, the offset may be compared to a threshold offset that will indicate that f(low) is sufficiently close to the lower limit of the rebar frequency band. If it is determined that the offset is acceptable, the identified low noise frequency may be displayed and / or automatically selected at step 1014. At step 1016, the operation may return to a full frequency selection process, which also selects a symbol frequency, such as Figure 12b 950. On the other hand, if at step 1010 it is determined that the offset is too high, the operation may be routed to step 1020 where an index value n is set that counts frequency increments for the noise scan of the rebar frequency band starting from the lower limit of the rebar frequency band (n=1) and ending at n(low), where n(low) represents the value of n at f(low). At step 1024, if the noise value for the frequency identified by the current value of n is within the limit range, the operation may proceed to step 1014. Note that the acceptable limit may be defined in any suitable manner, such as not exceeding some specified amount above the measured noise at f(low). If the noise is not within the limit range, the operation may proceed to step 1026 where n is incremented. Then, at step 1028, it is tested whether the current value of n is equal to n(low). If so, then at step 1030 f(low) may be displayed and / or automatically selected as the depth signal frequency. Thereafter, the operation may return to Figure 12bIf the value of n is less than n(low) at step 1028, the operation returns to step 1024 to compare the noise value at the indicated frequency with the acceptable limit, as described above. In this way, a loop is formed that tests the depth frequency of each increment of the scan up to f(low), so that an acceptable frequency can be found that is lower than the actual lowest noise frequency within the rebar frequency band.

[0084] Fig.13 1 is a flow chart illustrating one embodiment of a method of operating a locator 20 during underground operation, generally designated by reference numeral 1100. The method begins at step 1104 and proceeds simultaneously along a depth determination branch 1110 and a data recovery branch 1112. In the depth branch 1112, a depth signal is received at step 1120 and then the depth of the transmitter is determined at step 1124. Because the depth signal is transmitted on a dedicated frequency, the depth signal can be received substantially continuously throughout the underground operation. Thus, steps 1120 and 1124 are repeated in a loop throughout the normal operating mode of the locator. As described above, at step 1124, the depth of the transmitter can be determined using the depth signal based on the dipole equation. In one embodiment, a portion of the depth determination may include compensation for the distance of the locator above the ground. Upon receiving data from the RBL, RBM, and RBH bands (see Figure 6c ), note that the average signal strength of the signal can be used for depth determination. The data recovery branch 1112 begins at step 1130, which receives the data signal 122 in the form of a symbol stream, which can be composed of multi-bit symbols. At step 1134, the data signal 122 can be stored in, for example, the memory 714 (see Figure 9a) temporarily stores the symbol stream for decoding. In step 1138, the processor 710 decodes the symbol stream. In this regard, one of the symbols can be used as a synchronization symbol that can identify the beginning of the packet structure. In an embodiment using 4-bit symbols (i.e., 16 symbol frequencies), a seventeenth symbol frequency can be added to represent the synchronization symbol in the symbol stream. As a non-limiting example, a suitable packet structure can be represented by a series of 4-bit variables as S, P1, R1, P2, R2, BT1, BT2, R3, where S has a fixed value corresponding to the synchronization symbol, P1 represents the first four bits (0-3) of the pitch value, R1 is a first rolling variable that characterizes the rolling orientation, P2 is 4-7 bits of the pitch value, BT1 is 4-7 bits of battery and temperature data, BT2 is 4-7 bits of battery and temperature data, and R3 is a third rolling variable. In this regard, it should be understood that the pitch value is accumulated based on two different variables corresponding to two symbols in the symbol stream separated by another symbol. That is, the four bits of P2 can be added to the four bits of P1 to represent the complete pitch value. If necessary, additional bits can be added based on another pitch variable. Similarly, based on two continuous variables BT1 and BT2, eight bits of battery and temperature data can be combined. In step 1140, the data stream can be reassembled based on the decoded symbol stream to reconstruct the original data that is the basis of the symbol stream in the transmitter 130. In step 1144, the processor 710 recovers parameters from the data stream. These parameters can represent orientation parameters (such as pitch and roll), temperature, pressure, battery voltage and current, and any other data of interest. In step 1148, the processor 710 responds to the recovered parameters in any suitable manner, such as by driving the display 36 to display tilt and roll, battery status, temperature and pressure and / or as input to other processes, other processes including, for example, warnings when thresholds related to temperature and pressure are exceeded. Then, the operation returns to step 1130.

[0085] At this point, consideration of further details regarding the operation of transmitter 130 during underground operation is appropriate. Embodiments of the transmitter may flexibly allocate transmission power among the various frequencies (e.g., the frequencies shown in Tables 3 and 4) at which it is transmitted. In one embodiment, each frequency may be allocated an equal amount of transmission power. In another embodiment, the transmission power may be allocated unevenly among the frequencies. For example, one or more frequencies may be allocated a higher transmission power than another group of frequencies. In yet another embodiment, each frequency may be allocated a different transmission power. This power allocation may be performed in any suitable manner. For example, Figure 1The portable device 20 of FIG. 9 can be configured to monitor the average signal strength associated with each frequency while receiving each frequency during normal operation. The transmission power can then be reallocated between the frequencies on the fly based on the average signal strength on the fly. For example, a sudden drop in signal strength at a given frequency may be attributable to interference, and additional power may be allocated to that frequency. In some embodiments, relatively lower transmission powers may be allocated to low noise frequencies, while relatively higher transmission powers may be allocated to higher noise frequencies. The reallocated transmission power values ​​may be transmitted to the transmitter 130 in any suitable manner. For example, the portable device 20 may communicate the reallocated power scheme to the drill rig 80 via a telemetry signal 44. The drill rig may then communicate the new power scheme to the transmitter 130 via the drill string using the drill string as an electrical conductor. In another embodiment, the portable device 20 may be configured with an additional antenna 712 such as a dipole antenna (see FIG. 7 ). Figure 1 ), used to transmit a signal for direct reception by transmitter 130. The modulation of the signal can be decoded by transmitter 130 to recover the new power scheme.

[0086] See again Fig.10b , power allocation among selected frequencies can also be performed during the frequency selection process or mode before entering the normal mode or reinforcement mode. For example, power can be allocated based on the noise value associated with each selected frequency, such as Fig.10a and Fig.10b Although for illustrative purposes, Fig.10a and Fig.10b The low noise frequencies identified in the example appear to present relatively equal noise values, but this is not necessarily the case. If there is a significant change in the noise values ​​of the lowest noise frequencies identified, the transmission power can be allocated to those frequencies that present relatively high noise values ​​at a higher proportion. Conversely, the transmission power allocated to very low noise frequencies can be relatively low so that additional power can be allocated to one or more other frequencies. The transmission power can also be allocated in a manner consistent with the application of the blocking window as described above. For example, if a specific frequency is selected so that power line harmonics or other noise abnormally falls within the blocking window for the specific frequency, additional power can be allocated to the specific frequency. It should be understood that in any embodiment using an allocated transmission power that can vary with frequency, such allocation can be based on total power consumption, particularly when the transmitter 130 is battery powered. In this way, the total power consumption can be reduced, or the target total power consumption can be maintained.

[0087] Applicants recognize that, as disclosed herein, the transmission of depth signals at low frequencies in rebar mode relative to the extremely large data symbol frequencies raises particular concerns. In this regard, as the depth signal frequency decreases relative to a given data signal frequency, even without active interference and without any countermeasures, Applicants have observed that the range of depth signals that can be received decreases relative to the range of data signals that can be received. This can be very problematic during the course of operation because the locator 20 may indicate reception of the depth signal 120 long before the data signal 122 is lost. To ensure full system performance, the locator must receive both the depth signal and the data signal. While not intending to be bound by theory, Applicants believe that the reduction or attenuation of the low frequency range can be attributed to reduced coupling efficiency between the transmit antenna and the receive antenna. At the same time, the antenna primarily behaves as an inductor, such that the impedance of the antenna decreases as the frequency decreases. For a fixed drive voltage, the current increases in an at least approximately linear manner. Applicants have observed that the attenuation of the signal strength, and thus the range of the depth signal, is complex in nature. In an embodiment, to compensate for the attenuation, the appropriate transmit power can be characterized in any suitable manner (e.g., empirically). A multiplier table may compensate for this coupling attenuation effect, or a function may be determined, for example, based on a curve fit, for use by a processor of the transmitter to set the transmit power based on the frequency. In order to maintain at least approximately equal receive ranges for the depth signal and the data signal, for example, the depth signal may be adjusted to a power at least about 100 times higher than the data signal. This adjustment may accommodate downward adjustment of the power allocated to the data signal to accommodate rebalancing or shifting power to the depth signal, while allocating additional power to the data signal for the same reason, without exceeding a maximum power threshold or downward adjustment of the power allocated to the depth signal. In another example, for a depth signal frequency of 330 Hz and a data signal frequency of 18 KHz, the depth signal frequency may provide approximately 5 times the power of the data signal frequency. In view of these insights, the applicant discloses an advanced system in which a processor of the transmitter is used to generate a depth drive input and generate a data drive input at the depth signal frequency, and is also used to characterize sensor data in a manner that: the depth signal transmit power related to the data signal transmit power is controlled so that a first receive range of the depth signal at least approximately matches a second receive range of the data signal, even if the depth signal frequency is much lower (e.g., 1 KHz or less) than the data signal frequency. In other words, compensation is performed by balancing the transmit power between the depth signal and the data signal so that the received range between the two signals is at least approximately equal. At the same time, this balance can meet the further requirement of managing the overall power consumption of the transmitter so that, for example, a specified maximum power consumption is not exceeded. In one embodiment, the multiplier table 410 of Table 3 can be configured at least approximately based on the aforementioned attenuation characteristics, but this is not required. It should be apparent in Table 3 that the transmit power is based on the multiplier value.

[0088] The foregoing description of the present invention is given for the purpose of illustration and description. It is not intended to be exhaustive or to limit the present invention to the exact form or forms disclosed, and other modifications and variations may be implemented in view of the above teachings. Therefore, those skilled in the art should be able to recognize certain modifications, arrangements, additions and combinations of the above embodiments.

[0089] It is preferred to include all elements, parts and steps described herein. It should be understood that any one of these elements, parts and steps can be replaced by other elements, parts and steps or completely deleted for those skilled in the art.

[0090] In summary, at least the following is disclosed herein: A transmitter for use underground controls a depth signal transmission power relative to a data signal transmission power such that one reception range of the depth signal at least approximately matches another different reception range of the data signal. A portable device may form a system with the aforementioned transmitter, wherein the portable device scans a plurality of frequencies within at least one low frequency depth signal range to measure electromagnetic noise at each of the plurality of frequencies and identifies at least one frequency as a potential depth frequency of the transmitter. The portable device may include a dual mode filter having a rebar mode filter and a normal mode filter. The depth signal frequency may be dynamically located relative to the low frequency noise.

[0091] concept This article also discloses at least the following concepts.

[0092] Concept 1. A transmitter for use in conjunction with a horizontal directional drilling system, the horizontal directional drilling system including a drill string extending from a drill rig to an underground tool, the underground tool supporting the transmitter so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, the transmitter comprising: an antenna; one or more sensors for generating sensor data; an antenna driver for electrically driving the antenna to transmit a depth signal in response to a depth drive input for above-ground reception in determining the depth of the underground tool, and for electrically driving the antenna to transmit at least one data signal representing sensor data using at least one data signal frequency in response to the data drive input for above-ground recovery of the sensor data, the data signal frequency being higher in frequency than the depth signal; and a processor configured to generate the depth drive input at the depth signal frequency, and to generate the data drive input to characterize the sensor data in a manner that controls a depth signal transmission power related to the data signal transmission power so that one reception range of the depth signal at least approximately matches another different reception range of the data signal.

[0093] Concept 2. The transmitter of Concept 1 wherein the processor is further configured to adjust the depth signal reception range while adjusting the data signal reception range.

[0094] Concept 3. The transmitter of Concept 1 or 2 wherein the processor adjusts the data signal reception range and the depth signal reception range together such that the total power consumption of the transmitter does not exceed a specified limit.

[0095] Concept 4. The transmitter of Concepts 1-3 wherein the depth signal frequency is selectable within a range of depth signal frequencies.

[0096] Concept 5. The transmitter of Concept 4 wherein the processor is configured to adjust the depth drive input such that the depth signal reception range is at least approximately equal to the data signal reception range for any selected depth signal frequency within the depth signal frequency range.

[0097] Concept 6. The transmitter of Concept 4 or 5 wherein the depth drive input is a sine wave having an amplitude, the processor adjusting the depth signal reception range by varying the amplitude based at least in part on a particular location of the depth signal within the depth signal frequency range.

[0098] Concept 7. The transmitter of Concepts 1-6, wherein the processor generates a depth drive input and a data drive input such that a higher power is allocated to the depth signal than a higher power is allocated to the data signal, thereby increasing a data signal reception range that would otherwise be less than a depth signal reception range, and wherein each of the depth signal and the data signal is transmitted at the same power.

[0099] Concept 8. The transmitter of Concept 1-7 wherein the depth signal is less than 1 KHz.

[0100] Concept 9. The transmitter of Concept 1-7 wherein the depth signal is in the range of 300 Hz to 1 KHz (inclusive).

[0101] Concept 10. A transmitter for use in conjunction with a horizontal directional drilling system, the horizontal directional drilling system including a drill string extending from a drill rig to an underground tool, the underground tool supporting the transmitter so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, the transmitter comprising: antenna; one or more sensors for generating sensor data; an antenna driver for electrically driving the antenna to transmit a depth signal in response to the depth drive signal for above-ground reception to determine the depth of the underground tool, and for electrically driving the antenna to transmit a data signal representing sensor data using at least one data signal frequency for above-ground recovery of the sensor data, the data signal being higher in frequency than the depth signal; and A processor is configured to generate a depth drive signal at a depth signal frequency and to generate a data drive signal at a data signal frequency to control a first reception range of the depth signal to be related to a second reception range of the data signal.

[0102] Concept 11. A system comprising: a transmitter configured to move through the subsurface in the area during operation while transmitting a depth signal at a depth frequency selectable within a depth signal frequency range below 1 kHz to provide at least some immunity to passive interference, the depth signal also being affected by electromagnetic noise that can vary within the area; and A portable device is configured to scan a plurality of frequencies within a depth signal frequency range to measure electromagnetic noise at each of the plurality of frequencies and determine a lowest frequency of the frequencies as a potential depth frequency, the depth potential frequency meeting a low noise requirement based on the measured noise.

[0103] Concept 12. The system of Concept 11 wherein the low noise requirement compares the measured noise at each of a plurality of frequencies to a threshold as part of determining the potential depth frequency.

[0104] Concept 13. The system of Concept 11 wherein the low noise requirement is based on a relative comparison of electromagnetic noise measured at each of a plurality of frequencies.

[0105] Concept 14. The system of Concepts 11-13 wherein the portable device is configured to recommend potential depth frequencies to the user.

[0106] Concept 15. The system of Concepts 11-14 wherein the portable device is configured to automatically select the potential depth frequency as the depth frequency.

[0107] Concept 16. The system of Concept 15 wherein the portable device is configured to be overridden by the user selected depth frequency when the potential depth frequency is used as the depth frequency.

[0108] Concept 17. The system of Concept 11 wherein the portable device is configured at least to request user confirmation of the preferred depth frequency.

[0109] Concept 18. The system of Concepts 11-17 wherein the portable device is configured to, when the next lowest frequency in the frequency range is presented, determine at least one potential alternate depth frequency from the plurality of frequencies that is higher than the potential depth frequency among the plurality of frequencies that meet the noise requirement.

[0110] Concept 19. The system of Concept 18 wherein the portable device is configured to enter a real-time noise scanning mode to scan electromagnetic noise at the preferred depth frequency and the alternate depth frequency along the planned path and to display to the operator real-time noise values ​​corresponding to each of the preferred depth frequency and the alternate depth frequency.

[0111] Concept 20. The system of Concepts 11-19 wherein the portable device is further configured to scan a plurality of additional frequencies above 1 KHz to select at least one data signal frequency based on measuring electromagnetic noise at each of the plurality of frequencies above 1 KHz; and the transmitter further comprising one or more sensors that generate sensor data, and is configured to transmit the sensor data using at least the data signal frequency.

[0112] Concept 21. A portable device as part of a system in which a transmitter is configured to move through the subsurface in an area during an operation procedure while transmitting a depth signal, the portable device comprising: an antenna having an output; and A receiver is configured to scan a plurality of frequencies within a depth signal frequency range below 1 KHz to measure electromagnetic noise at each of the plurality of frequencies based on the antenna output and determine the lowest one of the frequencies as a potential depth frequency that meets the low noise requirement.

[0113] Concept 22. A portable device as part of a system in which a transmitter is configured to move through the subsurface in an area during an operation procedure while transmitting a depth signal, the portable device comprising: an antenna having an output; and A receiver configured to measure electromagnetic noise based on an antenna output in at least two different frequency bands below 1 kHz by incrementally scanning each frequency to generate a plurality of incremental noise readings in each frequency band, and displaying one or more potential depth frequencies in each frequency band for selection by an operator based on the incremental noise readings.

[0114] Concept 23. The portable device of Concept 22 wherein the receiver is further configured to select a potential depth frequency for each frequency band to correspond to a lowest frequency in the incremental noise readings from each frequency band and to display at least the potential depth frequencies for each frequency band for use in selecting another one of the potential depth frequencies as the depth frequency of the depth signal.

[0115] Concept 24. The portable device of Concept 22 wherein the portable device is configured to at least identify a depth frequency of a transmitter to transmit during a course of operation.

[0116] Concept 25. The portable device of Concept 23 or 24 wherein the portable device is configured to present a set of potential depth frequencies for selecting another one of the potential depth frequencies as an alternate depth frequency for the depth signal.

[0117] Concept 26. The portable device of Concept 25 wherein the portable device is further configured to determine a depth frequency and a backup depth frequency of the transmitter for transmission from the portable device during the course of operation.

[0118] Concept 27. The portable device of Concepts 23-26, wherein the portable device is configured to automatically select one of the potential depth frequencies for use as the depth frequency of the depth signal.

[0119] Concept 28. The portable device of Concepts 22-26 wherein the portable device is configured to enter a real-time noise display mode after displaying the set of potential depth frequencies to continuously display real-time noise readings for each potential depth frequency to an operator.

[0120] Concept 29. The portable device of Concept 28 wherein the portable device is configured for an operator to select one of the potential depth frequencies as the depth frequency of the depth signal during a real-time noise display mode.

[0121] Concept 30. The portable device of Concepts 22-29 wherein the portable device is configured to receive a depth signal from the transmitter during operation to determine a depth of the transmitter.

[0122] Concept 31. A system comprising: a transmitter configured to move through the subsurface in an area during operation while transmitting a depth signal at a depth frequency selectable within a depth signal frequency range below 1 KHz to provide at least some immunity to passive interference, the depth frequency also being affected by electromagnetic noise that can vary within the area; and A portable device configured to measure electromagnetic noise based on an antenna output in at least two different frequency bands below 1 kHz by progressively scanning each frequency to generate a plurality of incremental noise readings in each frequency band, and to display one or more potential depth frequencies in each frequency band for selection by an operator based on the incremental noise readings.

[0123] Concept 32. The system of Concept 31 wherein the portable device is further configured to select the potential depth frequency for each frequency band to correspond to a lowest frequency in the incremental noise readings from each frequency band, and to display at least the potential depth frequencies for each frequency band for selecting another one of the potential depth frequencies as the depth frequency of the depth signal.

[0124] Concept 33. A portable device as part of a system in which a transmitter is configured to transmit a depth signal at a depth frequency and transmit a data stream at one or more data frequencies while moving through the subsurface in an area during operation, the data stream being indicative of at least an orientation parameter of the transmitter, the portable device comprising: an antenna configured to receive the depth signal and the data frequency to generate an output; a switchable filter section configured to limit the antenna output in the normal mode to a frequency band above a predetermined frequency for transmitting the depth signal and the data stream at one or more frequencies, and to limit the antenna output in the rebar mode to another frequency band for transmitting the depth signal at frequencies below the predetermined frequency and for transmitting the data stream containing one or more frequencies above the predetermined frequency; and A processor is configured to switch the switchable filter portion between a normal mode and a rebar mode to recover the depth signal and the data stream in response to selection of the normal mode and the rebar mode.

[0125] Concept 34. The portable device of Concept 33 wherein the switchable filter comprises a normal mode filter for the normal mode and a rebar filter for the rebar mode.

[0126] Concept 35. The portable device of Concept 33 or 34, wherein the predetermined frequency is 1 KHz.

[0127] Concept 36. The portable device of Concept 34 or 35 wherein the rebar filter comprises a rebar mode lower filter corner below 1 KHz and the normal mode filter comprises a normal mode filter corner above 1 KHz.

[0128] Concept 37. The portable device of Concepts 34-36 wherein the rebar filter defines a rebar filter passband that is wider in bandwidth than a normal mode filter passband defined by the normal mode filter.

[0129] Concept 38. The portable device of Concept 37 wherein a first upper corner of the steel bar filter passband at least approximately matches a second upper corner of the normal mode filter passband.

[0130] Concept 39. The portable device of Concept 37 or 38, wherein the rebar filter passband allows additional low frequency noise compared to the normal mode frequency band, and the portable device is further configured to scan electromagnetic noise at least below a predetermined frequency to identify at least one low noise frequency used by the transmitter as a rebar mode depth frequency in the rebar frequency band to dynamically locate the rebar mode frequency relative to the additional low frequency noise.

[0131] Concept 40. The portable device of Concept 39 wherein the portable device is configured to transmit the identified low noise frequency to the transmitter for use as the depth signal frequency.

[0132] Concept 41. A system comprising: a transmitter configured to move through the subsurface in an area during operation while transmitting a depth signal at a selectable depth signal frequency, the selectable depth signal frequency being settable to any one of a plurality of incrementally spaced frequencies within a depth signal frequency range below 1 KHz to provide at least some immunity to passive interference, the depth signal also being susceptible to low frequency electromagnetic noise below 1 KHz that can vary within the area, and configured to transmit a data signal indicative of at least the orientation of the transmitter within a data frequency range above 1 KHz; and A portable device configured to scan a plurality of incrementally spaced frequencies below 1 KHz to measure electromagnetic noise at each of the plurality of incrementally spaced frequencies for use in identifying at least one low noise frequency associated with low frequency noise when setting a depth frequency in a transmitter.

[0133] Concept 42. The system of Concept 39 wherein the portable device is configured to transmit the identified low noise frequency to the transmitter for use as the depth signal frequency.

[0134] Concept 43. A portable device as part of a system comprising a transmitter for moving through underground in an area during an operation process, the portable device comprising: The receiver (i) configured to scan a plurality of incrementally spaced frequencies below 1 kHz to measure electromagnetic noise at each of the plurality of incrementally spaced frequencies to identify at least one low noise frequency used by the transmitter as a depth frequency to dynamically locate a depth signal frequency associated with the low frequency noise, and configured to identify at least one data signal frequency within a data frequency range above 1 kHz when transmitted from the transmitter to characterize at least one orientation parameter of the transmitter; and (ii) configured to detect a depth signal during operation to characterize at least the depth of the transmitter, and to detect a data signal to recover an orientation parameter during operation.

Claims

1. A frequency synthesizer, characterized in that: include: A first portion for generating a continuous frequency signal, the frequency of the continuous frequency signal being fixed with respect to time; and The second part is used to generate a discontinuous frequency signal, the frequency of which varies with time.

2. The frequency synthesizer according to claim 1, characterized in that The frequency synthesizer is a dual-channel direct digital synthesizer.

3. The frequency synthesizer according to claim 1, characterized in that The continuous frequency signal has a continuous amplitude.

4. A horizontal directional drilling system comprising a drill string extending from a drilling rig to an underground tool, the underground tool supporting the transmitter so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, characterized in that The system comprises a transmitter and a portable device, The transmitter comprises: antenna; one or more sensors for generating sensor data; an antenna driver for electrically driving the antenna to transmit a depth signal in response to the depth drive signal for above-ground reception in determining the depth of the underground tool, and for electrically driving the antenna to transmit a data signal representative of sensor data using at least one data signal frequency; and a processor for generating the depth drive signal at a depth signal frequency selectable within a depth signal frequency range below 1 KHz and generating the data drive signal at the data signal frequency; The portable device is used to measure electromagnetic noise based on the antenna output at at least two different frequencies below 1 KHz by gradually scanning each frequency to generate a plurality of noise readings, and display one or more target depth frequencies for an operator to select based on the plurality of noise readings.

5. The system according to claim 4, characterized in that The portable device is further configured to select the target depth frequencies corresponding to the lowest of the noise readings and to display at least the target depth frequencies for selecting one of the target depth frequencies as the depth frequency of the depth signal.

6. A system for horizontal directional drilling having a drill string extending from a drilling rig to an underground tool so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, characterized in that The system comprises: a transmitter comprising one or more sensors for measuring one or more operating parameters characterizing the inground tool, wherein the transmitter transmits these parameters characterizing the inground tool at two or more frequencies; and A portable device comprising, a receiver for receiving the two or more frequencies, and A processor is provided for recovering the operating parameters of the inground tool from the two or more frequencies.

7. A portable device for use in conjunction with a horizontal directional drilling system, the horizontal directional drilling system including a drill string extending from a drill rig to an underground tool, such that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, and the underground tool supports a transmitter that transmits an electromagnetic signal for detection by the portable device during underground operations, characterized in that The portable device comprises: a receiver for detecting signals from the transmitter above the ground and below the ground; and A processor is selectively operable to determine a range above the ground from the portable device to the transmitter and to determine a depth below the ground of the transmitter.

8. A frequency synthesizer, characterized in that: include: for generating a first portion of a first signal having a first frequency; a first amplitude controller for controlling the amplitude of the first signal; a second portion for generating a second signal having at least one second frequency different from the first frequency; and A second amplitude controller is used to control the amplitude of the second frequency independently of the first amplitude controller.

9. The frequency synthesizer according to claim 8, characterized in that The frequency synthesizer is a dual-channel direct digital synthesizer.

10. A method, characterized in that include: generating a continuous frequency signal using a first portion of a frequency synthesizer, wherein the frequency of the continuous frequency signal is fixed with respect to time; and A second portion of the frequency synthesizer is used to generate a discontinuous frequency signal whose frequency varies with time.

11. The method according to claim 10, characterized in that The frequency synthesizer is a dual-channel direct digital synthesizer.

12. The method according to claim 10, characterized in that The continuous frequency signal has a continuous amplitude.

13. A method of using a transmitter used in conjunction with a horizontal directional drilling system including a drill string extending from a drill rig to an underground tool, the underground tool supporting the transmitter so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, characterized in that The method comprises: generating sensor data using one or more sensors; electrically driving an antenna of the transmitter to transmit a depth signal in response to the depth drive signal for above-ground reception in determining the depth of the inground tool, and electrically driving the antenna of the transmitter to transmit a data signal representative of sensor data using at least one data signal frequency; generating the depth drive signal at a depth signal frequency selectable within a depth signal frequency range below 1 KHz and generating the data drive signal at the data signal frequency using a processor of the transmitter; Using a portable device, electromagnetic noise is measured based on the antenna output at at least two different frequencies below 1 KHz by progressively scanning each frequency to generate a plurality of noise readings, and one or more target depth frequencies are displayed for selection by an operator based on the plurality of noise readings.

14. A method of using a system in horizontal directional drilling having a drill string extending from a drill rig to an underground tool so that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, characterized in that The method comprises: measuring one or more operating parameters characterizing the inground tool using a transmitter including one or more sensors; transmitting, using the transmitter, at two or more frequencies, those conditions indicative of the inground tool; receiving the two or more frequencies using a receiver of the portable device; and The operating parameters of the inground tool are recovered from the two or more frequencies using a processor.

15. A method of using a portable device in conjunction with a horizontal directional drilling system, the horizontal directional drilling system including a drill string extending from a drill rig to an underground tool, such that the underground tool is moved through the ground by extending and retracting the drill string during underground operations, and the underground tool supports a transmitter that transmits an electromagnetic signal for detection by the portable device during underground operations, characterized in that The method comprises: detecting signals with the transmitter above the ground and below the ground using receivers; and determining, using a processor for selective operation, a range above ground level from the portable device to the transmitter; and The depth of the transmitter below the ground is determined using the processor.

16. A method, characterized in that include: generating a first signal using a first portion of a frequency synthesizer, the first signal having a first frequency; controlling the amplitude of the first signal using a first amplitude controller; generating a second signal using a second portion of the frequency synthesizer, the second signal having at least one second frequency different from the first frequency; and The amplitude of the second frequency is controlled using a second amplitude controller independently of the first amplitude controller.

17. The method according to claim 16, characterized in that The frequency synthesizer is a dual-channel direct digital synthesizer.

Images