An automatic measuring system of modulation parameters of radio signals

Abstract

The signal modulation measurement system of the present application comprises: a local signal source circuit module, outputting a local signal; an envelope detection circuit module, demodulating a single tone modulated common amplitude modulation wave signal; a stereo frequency modulation demodulation circuit module, demodulating a carrier frequency fixed frequency modulation wave signal; a high-speed electronic switch circuit module, switching the input of a signal to be measured into an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; switching the demodulated amplitude modulation wave signal or frequency modulation wave signal into an output channel; an active mixer circuit module, completing the mixing of the input radio signal to be measured and the local signal; a passive high-pass filter circuit module, serving as a frequency selection filter after the mixing of the input single tone modulated frequency modulation signal; and a single-chip microcomputer. Advantageous effects: the device can be started to measure by one key, the modulation type identification of the signal to be measured, the demodulated waveform output, and the measurement and display of the main modulation parameters are all automatically performed without manual intervention.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of analog radio signal demodulation, and particularly relates to a modulation parameter automatic measurement system of a radio signal. BACKGROUND

[0002] Analog modulation of high-frequency carrier signals, such as amplitude modulation and frequency modulation, is an important way to realize radio analog communication and is very common in actual communication systems. Modulation parameter measurement of a radio signal can quickly and accurately analyze the basic information of the radio signal, and modulation type identification of the radio signal is also very important in the cognition of a radio communication system.

[0003] However, a special measurement device that simultaneously has the functions of automatic modulation type identification of a radio signal, automatic demodulation waveform output of an amplitude modulation and frequency modulation signal, measurement of the carrier frequency, amplitude modulation index, frequency modulation index, maximum frequency deviation, and demodulation signal frequency of the amplitude modulation and frequency modulation signal, etc. is not common in radio civilian scenarios and radio experimental teaching. A spectrum analyzer can be used to distinguish amplitude modulation and frequency modulation signals, but generally cannot directly quantitatively measure parameters such as the amplitude modulation index of an amplitude modulation wave and the maximum frequency deviation of a frequency modulation wave. Moreover, the hardware cost of a spectrum analyzer is relatively high, the operation is complex, manual observation and reading are generally required for measurement and parameter calculation, and the automation degree of the measurement process is not high. Currently, there are some professional modulation domain measurement instruments, but these instruments are generally designed for frequency modulation radar and other equipment, are expensive, and have a working frequency band of GHZ or above, which is not suitable for low-cost civilian communication and radio experimental teaching needs. SUMMARY

[0004] In order to solve the problems in the prior art, the present application provides a modulation type identification of a radio signal and a signal modulation measurement system of main modulation parameters, which integrates functions such as automatic modulation signal type identification of a radio signal, automatic measurement and tracking of a carrier frequency, and automatic measurement of main modulation parameters, has wide application in fields such as automatic station searching, detection and positioning of outdoor radio signals, navigation communication of civilian ships, radio countermeasures, etc., and is also suitable for teaching demonstration and measurement instruments of communication and high-frequency circuit experiments. In order to achieve the above purpose, the technical scheme provided by the present application is as follows:

[0005] The modulation parameter automatic measurement system of the radio signal comprises:

[0006] The local oscillator signal source circuit module outputs a local oscillator signal containing a single-frequency sine wave signal and a continuous frequency-sweeping sine wave signal based on DDS;

[0007] The envelope detection circuit module is used to demodulate a single-frequency modulation ordinary amplitude modulation wave signal,

[0008] Stereo FM demodulation circuit module, for demodulating single frequency modulated FM wave signal with fixed carrier frequency, high-speed electronic switch circuit module, for switching the input AM wave demodulation channel or the FM wave demodulation channel of the signal to be measured; switching the demodulated AM wave signal or the FM wave signal into the output channel; switching the baseband signal after mixing of the signal to be measured or the demodulated AM wave signal or FM wave signal in the output channel for ADC sampling, active mixer circuit module, including a mixer, which mixes the input signal to be measured with the local oscillator signal, and shifts the frequency spectrum and carrier frequency of the input signal to be measured;

[0009] Passive high-pass filter circuit module, as a frequency selection filter after mixing of the input single frequency modulated FM wave signal, which selects the up-converted FM wave signal and inputs it into the stereo FM demodulation module;

[0010] Single-chip microcomputer, controlling the DDS to generate the local oscillator signal; controlling the high-speed electronic switch to perform ADC sampling and select the AM wave demodulation channel or the FM wave demodulation channel; calculating the modulation parameters including frequency, frequency spectrum, amplitude modulation index of the AM signal and frequency modulation index of the FM wave; judging the modulation type of the signal to be measured, and tracking and measuring the carrier frequency of the single frequency modulated FM wave and the unmodulated single frequency continuous carrier signal.

[0011] The further design of the modulation parameter automatic measurement system of the radio signal is that it further comprises an intermediate frequency amplifier circuit module, which amplifies the input single frequency modulated ordinary AM wave signal, so that the amplitude of the input AM wave signal reaches the input level requirement of the envelope detector module.

[0012] The further design of the modulation parameter automatic measurement system of the radio signal is that it further comprises a first active low-pass filter circuit, which is a filter for the baseband signal obtained by down-conversion of the externally input single frequency modulated FM wave signal through the mixer and the local oscillator signal.

[0013] The further design of the modulation parameter automatic measurement system of the radio signal is that it further comprises a second active low-pass filter circuit module, which performs low-frequency filtering on the modulation signal demodulated and output by the envelope detector module and the stereo FM demodulation module, filtering out high-frequency components and noise.

[0014] The further design of the modulation parameter automatic measurement system of the radio signal is that it further comprises a low-frequency amplifier circuit module, which amplifies the baseband signal after down-conversion of the mixer and the modulation signal demodulated and output by the stereo FM demodulation circuit module.

[0015] A further design of the automatic measurement system for modulation parameters of radio signals involves using a superheterodyne structure to downconvert the spectrum of the signal under test to the baseband, using a microcontroller to sample the downconverted signal, and performing an FFT transform to obtain the spectral characteristics of the signal.

[0016] A further design of the automatic measurement system for the modulation parameters of the radio signal is that the specific process by which the microcontroller determines the modulation type of the signal under test and tracks and measures the carrier frequencies of the single-frequency modulated FM wave and the unmodulated single-frequency continuous carrier signal is as follows:

[0017] The radio signal to be tested is selected by an electronic switch to first enter the amplitude modulation demodulation channel. The output of the envelope detection circuit is sent to the microcontroller for sampling. If the sampled signal is a standard single-frequency sine wave periodic signal, the input signal is determined to be a single-frequency modulated ordinary amplitude modulation wave.

[0018] If it is not a sine wave, the signal to be tested is input into the frequency modulation demodulation channel again through the electronic switch to determine the frequency modulation wave type and carrier frequency.

[0019] During the local oscillator signal frequency sweep, the microcontroller performs an FFT transformation on the sampled signal at each frequency point of the local oscillator signal to obtain the spectrum information of the radio signal under test after down-conversion. Then, based on the main characteristics of the spectrum analyzed by the microcontroller using FFT transformation on the sampled down-converted signal, if the spectrum obtained by FFT transformation of the sampled signal at a certain frequency of the local oscillator signal during the frequency sweep contains at least two or more spectral components near zero frequency, then the radio signal under test is determined to be a single-frequency modulated frequency-modulated wave. According to the spectrum characteristic analysis, when the frequency of the local oscillator signal is the same as the carrier frequency of the frequency-modulated wave under test, the corresponding local oscillator signal frequency f0 is recorded, where f0 is the carrier frequency of the frequency-modulated wave under test.

[0020] If, after a complete frequency sweep, the spectrum obtained by FFT transformation of the sampled signal does not show at least two frequency components with large amplitudes near zero frequency, then it can be determined that the signal under test is not a frequency-modulated wave, but an unmodulated single-frequency continuous carrier signal.

[0021] A further design of the automatic measurement system for the modulation parameters of the radio signal is that the microcontroller calculates the amplitude modulation index m of a single-tone modulated ordinary amplitude-modulated wave. a The specific process is as follows:

[0022] 1) Amplitude modulation index m of ordinary amplitude modulation wave a Calculation:

[0023] A single-frequency modulated AM wave can be described by the following mathematical expression:

[0024]

[0025] wherein, called the modulation index or the amplitude modulation degree, k a represents the sensitivity of amplitude modulation, V0 represents the amplitude of the unmodulated carrier, and V Ω represents the amplitude of the modulating signal;

[0026] According to equation (1), it can be derived that

[0027]

[0028] V max and V min respectively represent the maximum value and the minimum value of the envelope of the amplitude modulation wave;

[0029] Using the characteristic that the voltage transfer coefficient of the envelope detection circuit is basically unchanged (the voltage transfer coefficient is defined as: demodulation signal amplitude / amplitude of the input amplitude modulation wave envelope), the voltage transfer coefficient K d of the envelope detection circuit is measured in advance, the demodulation waveform amplitude U Ω is sampled and measured using a single-chip microcomputer, the envelope amplitude m a Vim of the general amplitude modulation wave is converted according to equation (3), and the amplitude modulation index m a of the to-be-measured amplitude modulation wave can be calculated.

[0030]

[0031] wherein, K d is the voltage transfer coefficient of the detector, U Ω is the output voltage of the envelope detection circuit, m a is the amplitude modulation index, and U i is the amplitude of the carrier voltage.

[0032] The further design of the modulation parameter automatic measurement system of the radio signal is that the single-chip microcomputer calculates the frequency modulation index m f and the maximum frequency deviation Δf m of the to-be-measured frequency modulation wave, and specifically includes the following steps:

[0033] Step 1) According to the characteristic that the slope of the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is basically unchanged in the linear region, the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is measured in advance;

[0034] Step 2) The slope of the frequency discrimination S curve, i.e., the frequency discrimination sensitivity k f of the stereo frequency modulation demodulation circuit, is calculated, the voltage amplitude V m of the output waveform of the frequency discriminator is sampled and measured by the single-chip microcomputer, the frequency f m of the demodulation waveform, i.e., the modulating signal, is calculated through FFT, and the frequency modulation index m fThe maximum frequency deviation Δf of the to-be-tested frequency modulation wave is calculated according to formula (4) m ;

[0035]

[0036] The frequency modulation index m of the to-be-tested frequency modulation wave is calculated according to formula (5) f .

[0037]

[0038] The beneficial effects of the present application are:

[0039] 1. The measuring device can automatically identify the input to-be-tested radio signal, and the identifiable signal modulation types include single-tone

[0040] amplitude modulation wave (AM wave) of ordinary amplitude modulation, frequency modulation wave (FM wave) of single-tone modulation, and unmodulated single-frequency continuous carrier.

[0041] 2. After the measuring device automatically identifies the modulation type of the to-be-tested radio signal, the signal demodulation function can be automatically completed at the same time

[0042] The output waveform signal-to-noise ratio is high and basically distortion-free. The main performance index parameters of the measuring device are as follows: the peak-to-peak value of the input carrier voltage ranges from 50 mV to 100 mV, the carrier frequency ranges from 10 MHz to 30 MHz, the input single-tone modulated amplitude modulation wave has an amplitude modulation index ranging from 0.2 to 1.0 and a modulation signal frequency ranging from 3 kHz to 5 kHz, and the input single-tone modulated frequency modulation wave has a frequency modulation index ranging from 1 to 6 and a modulation signal frequency ranging from 3 kHz to 10 kHz.

[0043] 3. The device simultaneously uses superheterodyne structure and zero intermediate frequency technology

[0044] The output frequency of the local oscillator signal source is stepped by a certain continuous

[0045] sweeping signal and mixes with the to-be-tested signal. After the output of the mixer is down-converted by a low-pass filter, the spectrum of the to-be-tested signal is moved to the baseband, then the single-chip microcomputer samples the baseband signal and performs FFT calculation, and the spectrum of the baseband signal is analyzed to determine whether the to-be-tested signal is a frequency modulation wave. By using this method, it can be quickly determined whether it is a frequency modulation wave by sweeping the local oscillator signal, and the carrier frequency of the frequency modulation wave is determined at the same time. Finally, the superheterodyne structure is used to realize frequency discrimination demodulation and output of the to-be-tested frequency modulation wave.

[0046] 5. The device according to the characteristics of the frequency discriminator S curve in the linear region slope is basically unchanged, pre-determined frequency discriminator S curve, using a single-chip microcomputer sampling and measuring the demodulation waveform voltage amplitude and frequency of the discriminator, can calculate the maximum frequency deviation of the frequency modulation wave, and calculate the corresponding frequency modulation index.

[0047] 6. The device of the local oscillator signal source based on integrated DDS chip design, make full use of the high frequency accuracy, frequency step continuous adjustable, sweep speed, output waveform phase noise, small harmonic distortion and other advantages. Can improve the judgment speed of the measured signal modulation type and the measurement accuracy of the carrier frequency of the frequency modulation wave, so as to further improve the modulation parameter measurement accuracy of the device, improve the signal-to-noise ratio of the demodulation waveform, and reduce the distortion degree.

[0048] 7. The device uses zero intermediate frequency technology in the process of judging the modulation type and measuring the carrier frequency of the frequency modulation wave, only needs to sample the baseband signal after mixing the measured signal, greatly reduces the requirement of ADC sampling rate of the processor, uses the integrated ADC of the single-chip microcomputer to meet the sampling demand, and does not need to use external high-speed ADC sampling circuit, greatly reduces the cost of hardware circuit and processor.

[0049] 8. In the measurement process, FFT transform is mainly used to analyze the frequency spectrum structure and the number of frequency spectrum components of the baseband signal, and the amplitude accuracy of the frequency spectrum component is very low, so the ordinary low-cost single-chip microcomputer can meet the performance requirement of FFT operation, which greatly reduces the cost of hardware circuit and processor. The device only uses low-cost STM32F4 series single-chip microcomputer as the main controller, has fast measurement speed and high measurement accuracy, and the parameter measurement error is basically within 10%.

[0050] 9. The device adopts full modular circuit design, and the extension and upgrade of measurement range and measurement function can be realized by adding or replacing optimized circuit modules. For example, a low-noise amplifier module and an AGC circuit module are added in front of the input channel of the measured signal, which can greatly expand the input dynamic range of the measured radio signal. The power range of the input signal in the actual measurement can be expanded to-40dBm to 0dBm.

[0051] 10. By changing the center frequency of the frequency discriminator circuit and the sweep range of the local oscillator signal source, the carrier frequency range of the measured radio signal can be expanded. The carrier frequency range can be expanded to 10MHz to 100MHz in actual measurement. The software control code of the single-chip microcomputer, ADC sampling, demodulation signal waveform period and amplitude measurement, FFT transform and spectrum component analysis code are optimized and upgraded. Using the hardware circuit of the device, the type judgment of the input digital modulated signal (including ASK, 2FSK, etc.) can also be realized, and the digital baseband signal demodulation can be completed. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 Module diagram of the automatic measurement system of the modulation parameters of the radio signal of the invention.

[0053] Figure 2 Circuit diagram of the local oscillator signal source.

[0054] Figure 3 Circuit diagram of the envelope detection circuit module.

[0055] Figure 4 Circuit diagram of the stereo FM demodulation module.

[0056] Figure 5 Circuit diagram of the high-speed electronic switch circuit module.

[0057] Figure 6 Circuit diagram of the mixer.

[0058] Figure 7 Circuit diagram of the passive high-pass filter.

[0059] Figure 8 Circuit diagram of the intermediate frequency amplifier.

[0060] Figure 9 Circuit diagram of the low-frequency amplifier.

[0061] Figure 10 Circuit diagram of the first active low-pass filter circuit module (-3dB cutoff frequency 60kHz).

[0062] Figure 11 Circuit diagram of the second active low-pass filter circuit module (-3dB cutoff frequency 12kHz).

[0063] Figure 12 Waveform diagram of the input AM signal (lower waveform) and the demodulated waveform (upper waveform) when the modulation index is maximum (m a = 1.0).

[0064] Figure 13 Waveform diagram of the input AM signal (lower waveform) and the demodulated waveform (upper waveform) when the modulation index is minimum (m a = 0.2).

[0065] Figure 14 Waveform diagram of the demodulated signal of the system when the input is a single-frequency modulated FM wave, the carrier frequency is 20MHz, the modulation frequency and the modulation index are maximum (modulation signal frequency f = 10kHz, modulation index m f = 6).

[0066] Figure 15The demodulation waveform diagram of the system for automatically measuring the modulation parameters of radio signals for a single frequency modulated frequency wave with a carrier frequency of 20 MHz, the smallest modulation frequency and modulation index (modulation signal frequency f = 3 kHz, frequency modulation index m f The demodulation waveform diagram of the system for automatically measuring the modulation parameters of radio signals for a single frequency modulated frequency wave with a carrier frequency of 20 MHz, the smallest modulation frequency and modulation index (modulation signal frequency f = 3 kHz, frequency modulation index m

[0067] Figure 16 The working flow chart of the system for automatically measuring the modulation parameters of radio signals for judging the modulation type of the signal to be measured.

[0068] Figure 17 The frequency spectrum distribution diagram of the single frequency modulated frequency wave to be measured when the carrier frequency of the single frequency modulated frequency wave to be measured is moved to the base band and the frequency of the local oscillator signal is the same as the carrier frequency of the single frequency modulated frequency wave to be measured (modulation signal frequency 5 kHz, maximum frequency deviation 10 kHz).

[0069] Figure 18 The frequency spectrum diagram obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal in the case of Figure 17 .

[0070] Figure 19 The frequency spectrum distribution diagram of the single frequency modulated frequency wave to be measured when the carrier frequency of the single frequency modulated frequency wave to be measured is moved to 100 kHz and the difference between the frequency of the local oscillator signal and the carrier frequency of the single frequency modulated frequency wave to be measured is 100 kHz (modulation signal frequency 10 kHz, maximum frequency deviation 60 kHz).

[0071] Figure 20 The frequency spectrum diagram obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal in the case of Figure 19 .

[0072] Figure 21 The frequency spectrum distribution diagram of the single frequency modulated frequency wave to be measured when the carrier frequency of the single frequency modulated frequency wave to be measured is moved to 200 kHz and higher frequencies and the difference between the frequency of the local oscillator signal and the carrier frequency of the single frequency modulated frequency wave to be measured is greater than or equal to 200 kHz (modulation signal frequency 10 kHz, maximum frequency deviation 60 kHz).

[0073] Figure 22 The frequency spectrum diagram obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal in the case of Figure 21 .

[0074] Figure 23 The frequency spectrum distribution diagram of the single frequency modulated frequency wave to be measured when the frequency of the local oscillator signal is the same as the carrier frequency of the single frequency modulated frequency wave to be measured.

[0075] Figure 24 The frequency spectrum diagram obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal in the case of Figure 23 .

[0076] Figure 25 When the difference between the frequency of the local signal and the frequency of the single-frequency continuous carrier wave to be measured is greater than or equal to 100 kHz, the carrier frequency of the signal to be measured is shifted to a frequency of 100 kHz or higher, and the single-chip microcomputer obtains a frequency spectrum diagram after performing FFT transformation on the sampled signal.

[0077] Figure 26 When the frequency of the local signal source is the same as the carrier frequency of the single-frequency modulated frequency-modulated wave to be measured, the single-chip microcomputer of the measurement system shifts the signal after sampling and mixing to the baseband, and obtains a measured frequency spectrum diagram (the carrier frequency of the frequency-modulated wave is 30 MHz, the frequency of the modulating signal is 5 kHz, and the maximum frequency deviation is 10 kHz) after performing FFT transformation.

[0078] Figure 27 When the frequency of the local signal source is 100 kHz different from the carrier frequency of the single-frequency modulated frequency-modulated wave to be measured, the single-chip microcomputer of the measurement system shifts the frequency-modulated wave signal after sampling and mixing to 100 kHz, and obtains a measured frequency spectrum diagram (the carrier frequency of the frequency-modulated wave is 30 MHz, the frequency of the modulating signal is 10 kHz, and the maximum frequency deviation is 60 kHz) after performing FFT transformation.

[0079] Figure 28 When the frequency of the local signal source is 200 kHz different from the carrier frequency of the single-frequency modulated frequency-modulated wave to be measured, the single-chip microcomputer of the measurement system shifts the frequency-modulated wave signal after sampling and mixing to 200 kHz, and obtains a measured frequency spectrum diagram (the carrier frequency of the frequency-modulated wave is 30 MHz, the frequency of the modulating signal is 10 kHz, and the maximum frequency deviation is 60 kHz) after performing FFT transformation.

[0080] Figure 29 When the frequency of the local signal source is the same as the carrier frequency of the single-frequency continuous carrier wave to be measured, the single-chip microcomputer of the measurement system shifts the signal after sampling and mixing to the baseband, and obtains a measured frequency spectrum diagram after performing FFT transformation.

[0081] (carrier frequency is 30 MHz)

[0082] Figure 30 When the frequency of the local signal source is 100 kHz different from the carrier frequency of the single-frequency continuous carrier wave to be measured, the single-chip microcomputer of the measurement system shifts the signal after sampling and mixing to 200 kHz, and obtains a measured frequency spectrum diagram (carrier frequency is 30 MHz) after performing FFT transformation.

[0083] Figure 31 Typical actual measurement display results of the modulation parameter automatic measurement system of the radio signal (the input signal to be measured is a common amplitude-modulated wave (AM wave) with a carrier frequency of 10 MHz, a modulating signal frequency of 2 kHz, and an amplitude modulation index of 1).

[0084] Figure 32 A typical actual measurement display result of the modulation parameter automatic measurement system of the radio signal of the present application (the input signal to be measured is a common amplitude modulation wave (AM wave) with a carrier frequency of 30 MHz, a modulation signal frequency of 2 kHz, and an amplitude modulation index of 0.2).

[0085] Figure 33 A typical actual measurement display result of the modulation parameter automatic measurement system of the radio signal of the present application (the input signal to be measured is a frequency modulation wave with a carrier frequency of 10 MHz, a modulation signal frequency of 10 kHz, and a frequency modulation index of 6, corresponding to a maximum frequency deviation of 60 kHz).

[0086] Figure 34 A typical actual measurement display result of the modulation parameter automatic measurement system of the radio signal of the present application (the input signal to be measured is a frequency modulation wave with a carrier frequency of 30 MHz, a modulation signal frequency of 3 kHz, and a frequency modulation index of 1, corresponding to a maximum frequency deviation of 3 kHz).

[0087] Figure 35 A typical actual measurement display result of the modulation parameter automatic measurement system of the radio signal of the present application (the input signal to be measured is a common amplitude modulation wave (AM wave) with a carrier frequency of 30 MHz, a modulation signal frequency of 2 kHz, and an amplitude modulation index of 0.2).

[0088] Figure 36 A typical actual measurement display result of the modulation parameter automatic measurement system of the radio signal of the present application (the input signal to be measured is a common amplitude modulation wave (AM wave) with a carrier frequency of 30 MHz, a modulation signal frequency of 2 kHz, and an amplitude modulation index of 0.2). DETAILED DESCRIPTION

[0089] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0090] As shown in the accompanying drawings Figure 1The signal modulation measurement system of the embodiment mainly comprises a local oscillator signal source circuit module, an envelope detection circuit module, a stereo frequency modulation demodulation circuit module, a high-speed electronic switch circuit module, an active mixer circuit module, a passive high-pass filter circuit module, an intermediate frequency amplifier circuit module, a first active low-pass filter circuit module, a second active low-pass filter circuit module, a low-frequency amplifier circuit module, and a single-chip microcomputer, etc. The local oscillator signal source circuit module outputs a local oscillator signal containing a single-frequency sinusoidal signal and a continuously swept sinusoidal signal based on DDS (digital frequency synthesis). The envelope detection circuit module is used for demodulating a general amplitude modulation wave signal. The stereo frequency modulation demodulation circuit module is used for demodulating a frequency modulation wave signal with a fixed carrier frequency. The high-speed electronic switch circuit module is used for switching the input amplitude modulation wave demodulation channel or the frequency modulation wave demodulation channel of the to-be-measured signal, switching the demodulated amplitude modulation wave signal or the frequency modulation wave signal into the output channel, and switching the baseband signal after the to-be-measured radio signal is mixed or the demodulated signal of the amplitude modulation wave or the frequency modulation wave signal in the output channel for ADC sampling. The active mixer circuit module comprises a mixer, an amplitude limiting amplifier, a low-noise output amplifier, and a bias circuit. The mixer completes the mixing of the input to-be-measured radio signal and the local oscillator signal, and shifts the frequency spectrum and the carrier frequency of the input to-be-measured radio signal. The passive high-pass filter circuit module is used as a frequency selection filter after the mixing of the to-be-measured single-tone modulation (modulation signal is a sinusoidal wave) frequency modulation signal, and the selected frequency modulation wave signal after frequency up-conversion is input into the stereo frequency modulation demodulation module. The single-chip microcomputer controls the DDS to generate the local oscillator signal, controls the high-speed electronic switch to perform ADC sampling and select the amplitude modulation wave demodulation channel or the frequency modulation wave demodulation channel, calculates the modulation parameters including the frequency, the frequency spectrum, the amplitude modulation index of the amplitude modulation signal, and the frequency modulation index of the frequency modulation wave, judges the modulation type of the to-be-measured signal, and tracks and measures the carrier frequency of the frequency modulation wave of the single-tone modulation (modulation signal is a sinusoidal wave). The signal modulation measurement system of the embodiment further comprises an oscilloscope for displaying the modulation parameters.

[0091] The to-be-measured radio signal types include a general amplitude modulation wave (AM wave) of single-frequency modulation (modulation signal is a sinusoidal wave), a frequency modulation wave (FM wave) of single-frequency modulation (modulation signal is a sinusoidal wave), and an unmodulated single-frequency continuous carrier signal. The input carrier voltage peak-to-peak value range is 50 mV-100 mV, the carrier frequency range is 10 MHz-30 MHz, the carrier frequency of the frequency modulation wave and the unmodulated single-frequency continuous carrier signal is distributed on the integer multiple frequency of 100 KHz, that is, the frequency resolution of the carrier is 100 KHz, the carrier frequency resolution of the general amplitude modulation wave is not limited, the amplitude modulation index range of the amplitude modulation wave is 0.2-1.0, and the modulation signal frequency range is 3 kHz-5 kHz; the frequency modulation index range of the frequency modulation wave is 1-6, and the modulation signal frequency range is 3 kHz-10 kHz.

[0092] In this embodiment, the local oscillator signal source circuit module uses the DDS chip AD9910, which can generate a frequency-gradient sine wave at clock frequencies up to 400MHz. See Appendix. Figure 2 This module can output single-frequency sine wave signals and continuously swept sine wave signals. The frequency of the output signal is continuously adjustable between 1MHz and 100MHz, and the power of the output signal is adjustable between -40dBm and 0dBm.

[0093] In this embodiment, the envelope detection circuit module uses the ADL5511 detector chip to demodulate single-tone modulated ordinary amplitude-modulated wave signals. See Appendix. Figure 3 The ADL5511 features excellent temperature stability and an input frequency range from DC to 6 GHz, referenced to an internal 1.1V reference voltage provided by the EREF pin. The ADL5511 employs proprietary rectification technology to eliminate the carrier wave of the input signal, revealing the true envelope of the modulated signal. Circuit testing shows that the envelope detection circuit can accurately acquire the envelope of ordinary amplitude-modulated (AM) signals with bandwidths up to 1 GHz and modulation indices in the range of 0.1–1, producing a distortion-free demodulated waveform with a high signal-to-noise ratio.

[0094] In this embodiment, the stereo FM demodulation circuit module is used to demodulate FM wave signals with a fixed carrier frequency. The circuit module uses the stereo FM demodulation chip JLAC2090 and adopts FM phase-locked loop modulation technology. The range of the input FM wave carrier frequency that can be received is 87MHz-108MHz. See Appendix. Figure 4 Appendix Figure 4 By grounding the power ground and audio ground at a single point near the power supply, digital noise can be significantly reduced. In this embodiment, a microcontroller is used to program the chip to set the carrier center frequency for receiving FM waves. During demodulation, the channel remains stable without frequency drift, and it features automatic channel search and storage functions. Furthermore, it automatically remembers the channel's volume and frequency when power is off. For the set FM stereo input channel, this FM demodulation module exhibits strong frequency stability, greatly reducing interference from other external radio signals. In this device, the carrier center frequency for receiving FM waves is programmed to be 100MHz. Testing shows that the stereo FM demodulation circuit has excellent performance indicators; after prolonged operation, the center frequency shows virtually no drift, the frequency discriminator circuit exhibits good linearity in its discriminator curve, and the output demodulated waveform is stable, has high signal-to-noise ratio, and is almost distortion-free. The stereo FM demodulation circuit module can use dual-channel demodulation and has advantages such as high integration, low power consumption, high sensitivity, high output signal-to-noise ratio, and ease of use.

[0095] In this embodiment, the high-speed electronic switch circuit module uses the high-speed electronic switch chip CH440G, see Appendix. Figure 5, support higher than 1kHz switching rate, while the frequency range of the input signal channel contains 10MHz to 30MHz band, high-speed electronic switch to realize the function of switching the input signal to be measured amplitude modulation wave demodulation channel and frequency modulation wave demodulation channel.

[0096] In this embodiment, the active mixer circuit module uses analog multiplier AD831 chip, see attached Figure 6 AD831 is an integrated mixer chip, including mixer, limiting amplifier, low noise output amplifier and bias circuit. When AD831 constitutes a mixer circuit, the bandwidth of the input signal and the local oscillator signal can be up to 500MHz, and the intermediate frequency output mode has two kinds, respectively, differential current output (output frequency can be up to 250MHz) and single-ended voltage output (output frequency can be up to 200MHz). The mixer circuit composed of AD831 has good linearity, the output impedance realizes 50Ω matching, the circuit itself has no insertion loss, through reasonable control of the power of the local oscillator signal and the input signal, the leakage of the combined frequency after mixing, the local oscillator and the input signal is small, basically no spurious components, the mixing circuit has good performance. The function of the mixer circuit module is to realize the function of mixing the input radio signal to be measured with the local oscillator signal, and to shift the frequency spectrum and carrier frequency of the input radio signal to be measured.

[0097] In this embodiment, the passive high-pass filter circuit module uses LC elements to constitute a nine-order Butterworth passive filter with a -3dB cutoff frequency of 30MHz, see attached Figure 7 The passive high-pass filter circuit module is used as a frequency selection filter after the frequency modulation signal mixing (up-conversion) of the input single frequency modulation (modulation signal is sine wave) to be measured. It filters out the down-conversion signal after mixing the input signal to be measured (frequency modulation signal) and the local oscillator signal, selects the frequency modulation wave signal after up-conversion, and inputs it into the stereo frequency modulation demodulation module to shift the carrier center frequency of the frequency modulation wave signal to 100MHz.

[0098] In this embodiment, the intermediate frequency amplifier circuit module uses a high-speed operational amplifier chip (OPA847), the working frequency range contains 10MHz to 100MHz band, the gain is 23dB and above, and the circuit schematic diagram of the module is shown in attached Figure 8 The intermediate frequency amplifier amplifies the input single frequency modulation (modulation signal is sine wave) of the ordinary amplitude modulation wave to be measured, improves the signal-to-noise ratio, and makes the amplitude of the input amplitude modulation wave to be measured meet the input level requirement of the envelope detection module.

[0099] In this embodiment, the low frequency amplifier circuit module uses an operational amplifier chip (OPA227), the working frequency range contains 100Hz to 1MHz band, the gain is 14dB and above, and the circuit schematic diagram of the module is shown in attached Figure 9The low frequency amplifier amplifies the baseband signal after the mixer down-converts and the modulated signal demodulated by the stereo FM demodulation circuit module.

[0100] In this embodiment, the active low-pass filter 1 circuit module uses the precision operational amplifier chip OPA227 to constitute a Butterworth fourth-order MFB filter, with a -3dB cutoff frequency of 60 kHz and a flat frequency response in the passband. The circuit schematic diagram of the module is shown in Fig. 2. Figure 10 The active low-pass filter 1 selects the baseband signal after the mixer (down-converts) of the input single-frequency modulated (modulation signal is a sine wave) FM wave signal as the baseband filter.

[0101] In this embodiment, the active low-pass filter 2 circuit module uses the precision operational amplifier chip OPA227 to constitute a Butterworth fourth-order MFB filter, with a -3dB cutoff frequency of 12 kHz and a flat frequency response in the passband. The circuit schematic diagram of the module is shown in Fig. 4. Figure 11 The active low-pass filter 2 performs low-pass filtering on the modulated signal demodulated by the envelope detection module and the stereo FM demodulation module, filters out high-frequency components and noise, reduces waveform distortion, and improves the signal-to-noise ratio.

[0102] The input impedance and output impedance of each circuit module are both 50 ohms, and coaxial lines are used to connect between modules; the ground of each module is one-point grounded with a 0 ohm resistor.

[0103] In this embodiment, the input channel of the stereo FM demodulation circuit module is set to 100 MHz. When it is determined that the input radio signal to be measured is a single-frequency modulated (modulation signal is a sine wave) FM wave, the carrier frequency f0 of the input FM signal to be measured is first determined by the continuous frequency sweep of the local oscillator signal source, and then the single-chip microcomputer controls the local oscillator signal source to output a single-frequency local oscillator signal with a frequency equal to 100 MHz-f0. For example, if the carrier frequency of the FM signal to be measured is determined to be 10 MHz, the local oscillator signal source is set to output a frequency of 90 MHz; if the carrier frequency of the FM signal to be measured is determined to be 20 MHz, the local oscillator signal source is set to output a frequency of 80 MHz. After the local oscillator signal and the input FM signal to be measured are multiplied by the mixer and then pass through the passive LC high-pass filter to obtain the up-converted FM signal, the carrier frequency of the input FM signal to be measured has become 100 MHz, which is aligned with the input fixed channel 100 MHz of the stereo FM demodulation module, so that the performance of the stereo FM demodulation module can be fully utilized. After the demodulated output signal is amplified by the low frequency amplifier and low-pass filtered, the final demodulated waveform output is obtained, which greatly improves the signal-to-noise ratio of the demodulated waveform, the working stability of the measuring device, and the measurement accuracy of the FM signal parameters.

[0104] In the embodiment, the measuring device has three electronic switches, all controlled by the single-chip microcomputer. The first electronic switch controls the input channel of the radio signal to be measured, and can switch the input signal to the AM wave demodulation channel or the FM wave demodulation channel. The second electronic switch controls the demodulation output port of the measuring device, and can switch the AM wave demodulation output or the FM wave demodulation output. The third electronic switch controls the ADC sampling signal channel of the single-chip microcomputer of the measuring device, and can switch the output demodulation signal of the measuring device or the baseband signal after the mixing (down-conversion) of the radio signal to be measured.

[0105] In the embodiment, the mixer performs the multiplication operation of the input radio signal to be measured and the local oscillator signal, and moves the frequency spectrum of the input radio signal to be measured to the desired position. When judging the type of the FM wave, the frequency spectrum of the input FM signal is moved to the baseband through mixing (down-conversion), the single-chip microcomputer samples the baseband signal and performs FFT spectrum analysis, and whether it is a FM wave is judged according to the composition of the spectrum components. When demodulating the FM wave, the frequency spectrum of the input FM signal is moved to the input fixed channel 100MHz of the stereo FM demodulation module through mixing (up-conversion), the performance of the stereo FM demodulation module is fully utilized, the output signal after demodulation is amplified and low-pass filtered to obtain the final demodulation waveform output, and the signal-to-noise ratio of the demodulation waveform is greatly improved, the working stability of the measuring device and the measurement accuracy of the parameters of the FM signal are improved.

[0106] In the embodiment, the radio signal to be measured after selection by the first high-speed electronic switch can be divided into two paths, one of which is input to the AM wave demodulation circuit channel, and the other of which is multiplied with the local oscillator signal through the mixer and then input to the FM wave demodulation circuit channel.

[0107] In the AM wave demodulation circuit channel, the signal to be measured is first amplified by a wideband intermediate frequency amplifier with a gain of 26dB to make the amplitude of the AM wave meet the input level requirement of the detector, then the original modulated signal is demodulated through the envelope detection circuit, and finally the high-frequency components, spurious signals and high-frequency noise contained in the demodulated signal are filtered out through a low-pass filter with a cutoff frequency of 12kHz to obtain the final monotonous AM wave demodulation waveform output.

[0108] In the embodiment, the demodulation of the AM wave and the measurement range of the modulation parameters of the device are as follows: the input is a single-frequency modulated (the modulated signal is a sine wave) AM wave, the carrier signal frequency range is 10MHz-30MHz, the modulated signal frequency range is 3kHz-5kHz, and the AM index range is 0.2-1.0. The input signal to be measured is an AM wave with a carrier frequency of 20MHz, a modulated signal frequency of 2kHz and an AM index of 1.0 (corresponding to the maximum measurable AM index), and the time-domain waveform of the demodulated signal (the upper waveform) and the input waveform of the AM wave (the lower waveform) are shown in the accompanying drawings. Figure 12The time-domain waveform of the demodulated signal (the upper waveform) and the input waveform of the AM wave (the lower waveform) are shown in the following figure: Figure 13

[0109] After determining the carrier frequency f0 of the FM signal, the frequency of the local oscillator signal is set to 100MHz-f0, and the carrier frequency of the to-be-measured FM signal is moved to a fixed 100MHz (corresponding to the fixed 100MHz input channel of the stereo FM demodulation module) through frequency up-conversion by the mixer, and then frequency discrimination is realized using the stereo FM demodulation module. The final demodulated waveform output is obtained after low-frequency amplification and low-pass filtering of the demodulated output signal.

[0110] In this embodiment, the demodulation of the FM wave and the modulation parameter measurement range of the system are as follows: the input is a single-frequency modulated (modulation signal is a sine wave) FM wave, the carrier signal frequency range is 10MHz-30MHz, among which the carrier frequencies of the FM wave and the unmodulated single-frequency continuous carrier signal are distributed on the integer multiple frequencies of 100KHz, that is, the frequency resolution of the carrier is 100KHz; the modulation signal frequency range is 3kHz-10kHz, and the FM index range is 1-6. The carrier frequency of the input to-be-measured FM wave is 20MHz, the modulation signal frequency is 10kHz, and the FM index is 6 (corresponding to the maximum measurable modulation frequency and the maximum frequency deviation). The time-domain waveform of the demodulated signal is shown in the following figure: Figure 14 Figure 15

[0111] The specific process of the single-chip microcomputer judging the modulation type of the to-be-measured signal is as follows: the to-be-measured radio signal is first selected to enter the AM demodulation circuit through the electronic switch, and the output of the envelope detection circuit is sent to the single-chip microcomputer for sampling. If the standard single-frequency sine wave periodic signal is sampled, it can be judged that the input signal is a single-frequency modulated (modulation signal is a sine wave) ordinary amplitude modulation wave.

[0112] If it is not a sine wave, the to-be-measured signal is input into the FM demodulation circuit module through the electronic switch again, and the FM wave type judgment and carrier frequency tracking measurement are performed.

[0113] ​​​In the frequency modulation wave type judging and demodulation circuit, a superheterodyne structure is adopted, the frequency step of the local oscillator signal source is 100KHz, the sweep frequency range is 10MHz-30MHz (covering the carrier frequency range of the input radio signal to be measured), the local oscillator signal and the input signal to be measured are mixed by an active mixer, the output signal of the mixer is subjected to a first active low-pass filter circuit with a cutoff frequency of 60kHz, the frequency spectrum of the radio signal to be measured is down-converted to the baseband, then subjected to voltage amplification by a low-frequency amplifier circuit, and finally input to the single-chip microcomputer for sampling after being switched by a high-speed electronic switch circuit. During the sweep of the local oscillator signal, the single-chip microcomputer performs FFT transformation on the sampling signal corresponding to each frequency point of the local oscillator signal, and the frequency spectrum information of the down-converted radio signal to be measured can be obtained. According to the FFT transformation of the down-converted signal sampled by the single-chip microcomputer, the main characteristics of the frequency spectrum are analyzed, and the modulation type of the signal to be measured is determined.

[0114] If, during the sweep, the frequency spectrum obtained by the FFT transformation of the sampling signal contains at least two frequency components with large amplitudes near the zero frequency when the local oscillator signal is at a certain frequency, as shown in Fig. 2, it can be determined that the radio signal to be measured is a single-frequency modulated (modulation signal is a sine wave) frequency modulation wave (FM wave). Figure 18 Figure 18 As can be seen from Fig. 2, at this time, the frequency of the local oscillator signal is the same as the carrier frequency of the frequency modulation wave to be measured, and the corresponding local oscillator signal frequency f0 is recorded, which is the carrier frequency of the frequency modulation wave to be measured. The single-chip microcomputer samples the down-converted signal, performs FFT transformation and spectrum characteristic analysis, and determines the modulation type, the principle of which has been described above and will not be repeated here.

[0115] If, after a complete sweep of the local oscillator signal, the frequency spectrum obtained by the FFT transformation of the sampling signal does not contain at least two frequency components with large amplitudes near the zero frequency (only one frequency component with a large amplitude near the zero frequency), it can be determined that the signal to be measured is not a frequency modulation wave, but an unmodulated single-frequency continuous carrier signal.

[0116] During the sweep of the local oscillator signal, when the frequency spectrum obtained by the FFT transformation of the sampling signal contains a frequency component with a large amplitude near the zero frequency, the frequency f0 of the local oscillator signal at this time is recorded, and according to the spectrum characteristic analysis and Fig. 3 described above, it can be determined that the frequency of the local oscillator signal is the same as the frequency of the unmodulated single-frequency continuous carrier signal to be measured, and f0 is the frequency of the unmodulated single-frequency continuous carrier signal to be measured. Figure 24

[0117] After the system determines and obtains the modulation type of the signal to be measured, the single-chip microcomputer is used to measure the amplitude modulation index m of the amplitude modulation wave with single-frequency modulation (modulation signal is a sine wave). a The specific process is as follows:​​

[0118] 1) Amplitude modulation index m of ordinary amplitude modulation wave a Calculation:

[0119] A single-frequency modulated AM wave can be described by the following mathematical expression:

[0120]

[0121] In the formula, This is called the amplitude modulation index or amplitude, k a V0 represents the amplitude of the unmodulated carrier wave, and V represents the amplitude of the amplitude modulation. Ω Indicates the amplitude of the modulated signal;

[0122] Based on equation (1), it can be derived that...

[0123]

[0124] V max and V min These represent the maximum and minimum values ​​of the amplitude-modulated wave envelope, respectively.

[0125] Taking advantage of the fact that the voltage transfer coefficient of the envelope detector circuit remains essentially constant (the voltage transfer coefficient is defined as: demodulated signal amplitude / amplitude of the input amplitude-modulated wave envelope), the voltage transfer coefficient K of the envelope detector circuit can be predetermined. d The amplitude U of the demodulated waveform is sampled and measured using a microcontroller. Ω According to equation (3), the envelope amplitude m converted to ordinary amplitude modulated wave is... a Vim allows us to calculate the amplitude modulation index m of the amplitude-modulated wave under test. a .

[0126]

[0127] Among them, K d U is the voltage transfer coefficient of the detector. Ω m is the output voltage of the envelope detector circuit. a U is the amplitude modulation index. i This represents the amplitude of the carrier voltage.

[0128] After determining and identifying the modulation type of the signal under test, this system uses a microcontroller to measure the maximum spectrum Δf of a single-frequency modulated (sine wave) frequency-modulated wave. m and frequency modulation index m f The specific process is as follows:

[0129] After tracking the carrier frequency f0 of the frequency modulated wave (FM wave) of the single frequency modulation (modulation signal is sine wave) to be measured, the frequency of the local oscillator signal source is set to 100MHz-f0, the carrier frequency of the frequency modulated wave to be measured is moved to a fixed 100MHz (corresponding to the fixed 100MHz FM wave input channel of the stereo frequency modulation demodulation circuit module) through the frequency conversion of the mixer, and then the stereo frequency modulation demodulation circuit module is used to realize the demodulation of the frequency modulated wave, i.e. frequency discrimination, and the final demodulation waveform output is obtained after the demodulation output signal passes through the second active low-pass filter and the low-frequency amplifier.

[0130] Step 1) According to the characteristic that the slope of the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is basically unchanged in the linear region, the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is measured in advance;

[0131] Step 2) The slope of the frequency discrimination S curve, i.e. the frequency discrimination sensitivity k of the stereo frequency modulation demodulation circuit, is calculated f , the voltage amplitude V of the output waveform of the frequency discriminator is sampled and measured by the single-chip microcomputer m , the frequency f of the demodulation waveform, i.e. the modulation signal, is calculated by FFT m , the corresponding maximum frequency deviation Δf of the frequency modulated wave to be measured is calculated according to the frequency discrimination sensitivity k f , according to formula (14) m ;

[0132]

[0133] The frequency modulation index m corresponding to the frequency modulated wave to be measured is calculated according to formula (15) f .

[0134]

[0135] The output of the envelope detection circuit passes through a low-pass filter to obtain the demodulation waveform of the amplitude modulation wave; the single-chip microcomputer ADC samples the demodulation waveform, calculates and measures, and simultaneously displays the modulation type of the signal to be measured, the waveform, frequency, spectrum of the demodulation signal, and the amplitude modulation index of the amplitude modulation signal, etc. Main modulation parameters on the liquid crystal screen.

[0136] When it is judged that the signal to be measured is a frequency modulated wave (FM wave) of single frequency modulation (modulation signal is sine wave), the high-speed electronic switch circuit module switches the input channel of the frequency modulated wave demodulation circuit of the signal to be measured, and the output of the frequency discriminator circuit passes through low-pass filtering and amplification to obtain the demodulation waveform of the frequency modulated wave; the single-chip microcomputer ADC samples the demodulation waveform, calculates and measures, and simultaneously displays the modulation type of the signal to be measured, the waveform, frequency, spectrum of the demodulation signal, and the frequency modulation index of the frequency modulation signal, etc. Main modulation parameters on the liquid crystal screen.

[0137] When judging the signal to be measured as an unmodulated single-frequency continuous carrier signal, the single-chip microcomputer measures the frequency of the carrier signal and simultaneously displays the modulation type and carrier frequency of the signal to be measured on the liquid crystal screen.

[0138] As Figure 16 , the software code algorithm for discriminating whether the modulation type is single-frequency modulation (modulation signal is a sine wave) AM wave is as follows: the single-chip microcomputer collects the final output signal of the AM demodulation circuit through ADC, and measures and calculates the peak-to-peak value of the demodulation signal. In order to reduce the measurement error caused by the jitter of the demodulation waveform during ADC collection, the fourth maximum value and the fourth minimum value of the demodulation waveform within a certain sampling time are measured respectively, the peak value of the demodulation waveform is obtained by subtracting the two values, and the average value is taken after multiple measurements. Set a suitable voltage threshold, compare the average value of the demodulation signal measurement with the threshold, if greater than the threshold, it is judged that the demodulation waveform is a sine wave, and the modulation type of the input signal to be measured is single-tone modulation AM wave. The above content is executed in the program code every small period of time, if the average value of the demodulation signal measurement is less than the threshold, it is judged that the input signal to be measured is not a single-tone modulation AM wave.

[0139] The software code algorithm for discriminating whether the modulation type is single-frequency modulation (modulation signal is a sine wave) FM wave or unmodulated single-frequency continuous carrier signal is as follows: the single-chip microcomputer controls the output of the continuous sweep signal of the local oscillator signal source, the sweep frequency range is set to 10MHz-30MHz (covering the carrier frequency range of the input radio signal to be measured), and the sweep step is set to 100kHz.

[0140] At each frequency point in the sweep process of the local oscillator signal, the single-chip microcomputer samples the baseband signal output by the mixer after passing through the first active low-pass filter circuit with a cutoff frequency of 60KHz, and performs FFT transform on the sampling signal to analyze the frequency spectrum of the baseband signal. If during the sweep process of the local oscillator signal, at a certain frequency corresponding to the local oscillator signal, the frequency spectrum obtained by FFT transform of the sampling signal contains at least two or more amplitude larger spectral components near zero frequency, as shown in FIG. 4, it can be judged that the radio signal to be measured is a single-frequency modulation (modulation signal is a sine wave) FM wave, according to the spectrum feature analysis and FIG. 4 described above. Figure 18 Figure 18 ​It can be seen that the frequency of the local oscillator signal is the same as the carrier frequency of the frequency-modulated wave under test at this time. Record the corresponding local oscillator signal frequency f0, where f0 is the carrier frequency of the frequency-modulated wave under test. Then, the loop is exited, and the frequency sweeping process is temporarily suspended. If, after a complete round of continuous frequency sweeping, the spectrum obtained by the FFT transformation of the sampled signal does not show at least two frequency components with large amplitudes near zero frequency (only one frequency component with large amplitude appears near zero frequency), then it can be determined that the signal under test is not a frequency-modulated wave, but an unmodulated single-frequency continuous carrier signal. During the frequency sweeping process of the local oscillator signal, when the spectrum obtained by the FFT transformation of the sampled signal shows a frequency component with large amplitude near zero frequency, record the local oscillator signal frequency f0 at this time. Based on the spectral characteristic analysis and appended... Figure 24 It can be seen that at this time, the frequency of the local oscillator signal is the same as the frequency of the unmodulated single-frequency continuous carrier. f0 is the frequency of the unmodulated single-frequency continuous carrier to be measured. The loop ends and the frequency sweeping process is temporarily suspended.

[0141] Taking a single-tone modulated FM wave with a carrier frequency of 10MHz, a modulation signal frequency of 5kHz, and a maximum frequency deviation of 20kHz as an example, the test results during the frequency sweep process are shown in the appendix. Figure 26 , 27 As shown in Figure 28. When the output frequency of the local oscillator signal source is the same as the carrier frequency of the FM wave to be measured during the frequency sweep process, as shown in the attached figure. Figure 26 As shown, the baseband signal spectrum measured by the microcontroller clearly shows large and clear spectral lines at positions such as 5kHz and 10kHz; when the difference between the output frequency of the local oscillator signal source and the carrier frequency of the FM wave under test is equal to 100kHz during the frequency sweep process, as shown in the attached figure... Figure 27 As shown, the baseband signal spectrum measured by the microcontroller shows residual high-order sideband components with small amplitudes near 2kHz and 12kHz; when the output frequency of the local oscillator signal source differs from the carrier frequency of the FM wave under test by more than or equal to 200kHz during frequency sweeping, as shown in the attached figure... Figure 28 As shown, the baseband signal spectrum measured by the microcontroller no longer shows any obvious and clear spectral line components with large amplitude.

[0142] Taking the test of an unmodulated single-frequency continuous carrier signal with a carrier frequency of 10MHz as an example, the test results during the frequency sweep process are shown in the appendix. Figure 29 As shown in Figure 30. When the output frequency of the local oscillator signal source is the same as the unmodulated single-frequency continuous carrier frequency to be measured during the frequency sweep process, as shown in the attached figure. Figure 29 As shown, the spectrum of the down-conversion signal measured by the microcontroller clearly shows large and clear spectral lines near the low-frequency position; when the output frequency of the local oscillator signal source is different from the unmodulated single-frequency continuous carrier frequency under test (with a phase difference of 100KHz or more), as shown in the attached figure... Figure 30As shown in the figure, the single-chip microcomputer can not see the obvious amplitude larger and clear spectrum line component near the low frequency position on the down-converted signal spectrum diagram.

[0143] The actual measurement process verifies that the method proposed in the embodiment, which uses the superheterodyne structure to move the spectrum of the signal to be measured to the baseband, uses the single-chip microcomputer to sample the down-converted signal, completes the FFT transformation to obtain the spectral characteristics of the signal, and judges the frequency modulation wave type and measures the carrier frequency, can correctly realize the judgment of the frequency modulation wave type of the single-frequency modulation (the modulation signal is a sine wave), and accurately and quickly measure the carrier frequency of the frequency modulation wave.

[0144] The specific process of obtaining the spectral characteristics of the signal by FFT transformation is as follows: first, the local oscillator signal source outputs a frequency step of 100KHz sweep signal, and the sweep frequency range is 10MHz-30MHz (covering the carrier frequency range of the input radio signal to be measured), the local oscillator signal and the input signal to be measured are mixed by the active mixer, and the output signal of the mixer is filtered by the first active low-pass filter circuit with a cutoff frequency of 60kHz, so as to move the spectrum of the radio signal to be measured to the baseband. The down-converted radio signal to be measured is voltage amplified by the low-frequency amplifier circuit, and finally input to the single-chip microcomputer for sampling through the high-speed electronic switch circuit. During the sweep process of the local oscillator signal, the single-chip microcomputer performs FFT transformation on the sampling signal corresponding to each frequency point of the local oscillator signal, and the spectral information of the down-converted radio signal to be measured can be obtained.

[0145] If the input signal to be measured is a single-frequency modulation frequency modulation wave, according to the requirement of the measurement system that the carrier frequency resolution of the frequency modulation wave is 100KHz (i.e. the carrier frequency of the frequency modulation wave is located at an integer multiple of 100KHz), the sweep step of the local oscillator signal is 100KHz, and during the sweep process, the spectral information obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal has the following three cases.

[0146] 1) When the frequency of the local oscillator signal is the same as the carrier frequency of the frequency modulation wave to be measured, the spectrum of the frequency modulation wave to be measured is moved to the baseband, and according to the theory, the distribution of the sideband components in its spectrum should be as shown in the attached Figure 17 (5KHz modulation signal frequency, 10KHz maximum frequency deviation).

[0147] The actual spectral distribution obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal is shown in the attached Figure 18 . The sampling frequency fs of the single-chip microcomputer is 62KHz, and the distribution of the sideband components with larger amplitude in the spectral distribution is symmetrically distributed about fs / 2, i.e. 31KHz.

[0148] 2) When the difference between the frequency of the local oscillator signal and the carrier frequency of the frequency modulation wave is equal to 100KHz, the carrier frequency of the frequency modulation wave to be measured is moved to

[0149] 100KHz frequency, most of its spectral components are outside the passband of the low-pass filter, and only a few small-amplitude high-order sideband components are retained within the passband of the low-pass filter. According to the theory, the distribution of the sideband components in the spectrum should be as shown in Fig. 4 (the frequency of the modulating signal is 10KHz, and the maximum frequency deviation is 60KHz). Figure 19

[0150] The actual spectral distribution obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal is shown in Fig. 5. The sampling frequency fs of the single-chip microcomputer is 62KHz, and the small-amplitude high-order sideband components remaining in the spectral distribution are symmetrically distributed about fs / 2, i.e. 31KHz. Figure 20

[0151] 3) When the difference between the frequency of the local oscillation signal and the carrier frequency of the frequency-modulated wave is greater than or equal to 200KHz, the carrier frequency of the frequency-modulated wave to be measured

[0152] is moved to a frequency of 200KHz or higher, and all its spectral components are outside the passband of the low-pass filter, and the spectrum does not contain any component, as shown in Fig. 7 (the frequency of the modulating signal is 10KHz, and the maximum frequency deviation is 60KHz). Figure 21

[0153] The actual spectral distribution obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal is shown in Fig. 8. The sampling frequency fs of the single-chip microcomputer is 62KHz, and the spectrum does not contain any component after the FFT transformation. Figure 22

[0154] When the input signal to be measured is an unmodulated single-frequency continuous carrier signal, according to the requirement of the measurement system that the carrier frequency resolution is 100KHz (i.e. the unmodulated single-frequency continuous carrier signal is located at an integer multiple of 100KHz), the frequency sweep step of the local oscillation signal is 100KHz, and the spectral information obtained by the single-chip microcomputer after performing FFT transformation on the sampling signal has the following two cases.

[0155] 1) When the frequency of the local oscillation signal is the same as the frequency of the unmodulated single-frequency continuous carrier to be measured, the spectrum of the signal to be measured is moved to the base

[0156] band, and according to the theory, the spectrum should not contain any frequency component. In the actual measurement of the system, since the local oscillation signal and the unmodulated single-frequency continuous carrier signal come from different frequency sources and are non-coherent signals, their frequencies are not exactly the same. Assuming that the frequency difference between the two is deltaf (less than 1KHz), after the low-pass filter, the spectrum contains only a spectral component with a frequency of deltaf, as shown in Fig. 9. Figure 23

[0157] ​​​​​The actual frequency spectrum diagram obtained after the single-chip microcomputer performs FFT transformation on the sampling signal will have a low-frequency component deltaf, as shown in the accompanying Figure 24

[0158] 2) When the difference between the frequency of the local signal and the frequency of the to-be-measured unmodulated single-frequency continuous carrier is greater than or equal to 100 KHz, the carrier frequency of the to-be-measured signal is moved to a frequency of 100 KHz and higher, and all the spectral components thereof are located outside the passband of the low-pass filter, are filtered out by the low-pass filter, and the spectrum no longer contains any component.

[0159] The actual frequency spectrum distribution obtained after the single-chip microcomputer performs FFT transformation on the sampling signal is shown in the accompanying Figure 25 The sampling frequency fs of the single-chip microcomputer is 62 KHz, and the spectrum no longer contains any component after FFT transformation, as shown in the accompanying Figure 25

[0160] In this embodiment, the signal modulation measurement system uses an STM32F407 single-chip microcomputer as the main controller and computing core unit of the device system, and the key input and liquid crystal display screen are used as the human-computer interface input device and output display device of the measurement system, respectively. The measurement system is easy to operate and does not require human control intervention. It can be automatically started by one key to identify the modulation type of the input to-be-measured signal (including amplitude modulation wave of single-frequency modulation (modulation signal is a sine wave), frequency modulation wave of single-frequency modulation (modulation signal is a sine wave), and unmodulated continuous single-frequency carrier signal), and the judgment result of the modulation type, the amplitude modulation index of the amplitude modulation wave, the carrier frequency of the frequency modulation wave, the corresponding frequency modulation index, the maximum frequency deviation, the demodulation signal waveform, the modulation signal frequency, and the modulation signal spectrum diagram are displayed on the liquid crystal screen in real time. Meanwhile, the demodulation waveforms of the amplitude modulation wave and the frequency modulation wave are automatically output.

[0161] In this embodiment, multiple test points are reserved in the measurement system, and the local signal waveform, the output waveform of the mixer, and the frequency response of each filter can be observed. Meanwhile, the demodulation output waveforms of the amplitude modulation wave and the frequency modulation wave can be externally connected to an oscilloscope for observation.

[0162] In this embodiment, the typical actual measurement display result of the signal modulation measurement system of the present application is shown in the accompanying Figures 31 to 36 .

[0163] The actual frequency spectrum diagram obtained after the single-chip microcomputer performs FFT transformation on the sampling signal will have a low-frequency component deltaf, as shown in the accompanying Figure 31 ​​The corresponding input signal to be measured is a common amplitude modulation wave with carrier frequency 10MHz, single frequency modulation (modulation signal is sine wave) with modulation signal frequency 2kHz and amplitude modulation index 1. The liquid crystal screen of the measuring system displays the automatic measurement results, the modulation type is judged as single tone modulation of amplitude modulation wave, the modulation signal frequency is 2.016kHz and the amplitude modulation index is 1.0, and the waveform diagram of the amplitude modulation wave demodulation output, the modulation signal spectrum diagram and other information are displayed. From the measurement data displayed on the screen, it can be seen that the modulation type judgment is correct, the demodulation signal frequency measured is 2.016kHz, the relative error of frequency measurement is 0.8%; the measurement result of the amplitude modulation index is 1.0, and the relative error is almost 0%.

[0164] attached Figure 32 The corresponding input signal to be measured is a common amplitude modulation wave with carrier frequency 30MHz, single frequency modulation (modulation signal is sine wave) with modulation signal frequency 2kHz and amplitude modulation index 0.2. The liquid crystal screen of the measuring system displays the automatic measurement results, the modulation type is judged as single tone modulation of amplitude modulation wave, the modulation signal frequency is 2.016kHz and the amplitude modulation index is 0.215, and the waveform diagram of the amplitude modulation wave demodulation output, the modulation signal spectrum diagram and other information are displayed. From the measurement data displayed on the screen, it can be seen that the modulation type judgment is correct, the demodulation signal frequency measured is 2.016kHz, the relative error of frequency measurement is 0.8%; the measurement result of the amplitude modulation index is 0.215, and the relative error is 7.5%.

[0165] The measurement results show that the system correctly judges the type of the input common amplitude modulation wave (AM wave) with single frequency modulation (modulation signal is sine wave), and the measured amplitude modulation index m a The maximum relative error of the measured demodulation signal frequency is 0.8%. The data recording results of multiple experimental tests on different carrier frequencies and modulation parameters are shown in the measurement data table attached Figure 27 The system correctly judges the type of the input common amplitude modulation wave, and the measurement accuracy of the amplitude modulation wave parameters is high. The maximum error of the carrier signal frequency and the amplitude modulation index in the continuous 10 times of measurement results of the same amplitude modulation wave parameters is within 8%.

[0166] attached Figure 33The corresponding input signal to be measured is a single frequency modulation (modulation signal is a sine wave) frequency modulation wave (FM wave) with a carrier frequency of 10 MHz, a modulation signal frequency of 10 kHz, a frequency modulation index of 6, and a maximum frequency deviation of 60 kHz. The liquid crystal screen of the measurement system displays the automatic measurement results, the modulation type is judged to be an FM wave, the modulation signal frequency is 10.019 kHz, the frequency modulation index is 5.915, the maximum frequency deviation is 59.265 kHz, and the waveform diagram of the FM wave demodulation output, the modulation signal spectrum diagram and other information are displayed. From the measurement data displayed on the screen, it can be seen that the modulation type judgment is correct, the measured carrier signal frequency is 10000 kHz, i.e. 10 MHz, and the relative error is almost 0%; the measured demodulation signal frequency is 10.019 kHz, and the relative error of the frequency measurement is 0.19%; the measurement result of the frequency modulation index m f is 5.915, the relative error is 1.42%, and the measurement result of the maximum frequency deviation Δf m is 59.265 kHz, and the relative error is 1.23%.

[0167] The Figure 34 corresponding input signal to be measured is a single frequency modulation (modulation signal is a sine wave) frequency modulation wave (FM wave) with a carrier frequency of 30 MHz, a modulation signal frequency of 3 kHz, a frequency modulation index of 1, and a maximum frequency deviation of 3 kHz. The liquid crystal screen of the measurement system displays the automatic measurement results, the modulation type is judged to be an FM wave, the modulation signal frequency is 3.024 kHz, the frequency modulation index m f is 0.996, the maximum frequency deviation Δf m is 3.012 kHz, and the waveform diagram of the FM wave demodulation output, the modulation signal spectrum diagram and other information are displayed. From the measurement data displayed on the screen, it can be seen that the modulation type judgment is correct, the measured carrier signal frequency is 30000 kHz, i.e. 30 MHz, and the relative error is almost 0%; the measured demodulation signal frequency is 3.024 kHz, and the relative error of the frequency measurement is 0.8%; the measurement result of the frequency modulation index m f is 0.996, the relative error is 0.4%, and the measurement result of the maximum frequency deviation Δf m is 3.012 kHz, and the relative error is 0.4%.

[0168] The measurement results show that the system correctly judges the type of the input single frequency modulation (modulation signal is a sine wave) frequency modulation wave, the relative error of the measured carrier frequency is almost 0%, the maximum relative error of the measured demodulation signal frequency is 0.4%, and the maximum relative error of the measured frequency modulation index m f is 1.42%. The measurement result of the maximum frequency deviation Δf mThe maximum relative error is 1.23%. After multiple tests, the device correctly judges the type of the input single-frequency modulated (modulation signal is a sine wave) frequency modulation wave, and the measurement accuracy of the frequency modulation wave parameters is high. The measurement error of the main modulation parameters is basically within 5%.

[0169] Attached Figure 35 The corresponding input signal to be tested is an unmodulated single-frequency continuous carrier signal with a carrier frequency of 10 MHz. The liquid crystal screen of the measurement system displays the automatic measurement results. The modulation type is judged to be an unmodulated single-frequency continuous carrier signal, and the carrier signal frequency is 10000KHz, i.e. 10MHz. As can be seen from the measurement data displayed on the screen, the modulation type is correctly judged, and the error of the measured carrier signal frequency is almost 0%.

[0170] Attached Figure 36 The corresponding input signal to be tested is an unmodulated single-frequency continuous carrier signal with a carrier frequency of 30MHz. The liquid crystal screen of the measurement system displays the automatic measurement results. The modulation type is judged to be an unmodulated single-frequency continuous carrier signal, and the carrier signal frequency is 30000KHz, i.e. 30MHz. As can be seen from the measurement data displayed on the screen, the modulation type is correctly judged, and the error of the measured carrier signal frequency is almost 0%.

[0171] The measurement results show that the system correctly judges the type of the input unmodulated single-frequency continuous carrier signal, and the relative error of the measured carrier frequency is almost 0%.

[0172] From the modulation type judgment and parameter measurement results attached Figures 31-36 , it can be shown that the device correctly judges the type of the input single-frequency modulated (modulation signal is a sine wave) ordinary amplitude modulation wave (AM wave), single-frequency modulated (modulation signal is a sine wave) frequency modulation wave (FM wave), and unmodulated single-frequency continuous carrier signal. The maximum relative error of the measured demodulation signal frequency of the AM wave is 2.4%, the maximum relative error of the measured demodulation signal frequency of the FM wave is 2.0%, the maximum relative error of the measured amplitude modulation index m a is 8.0%, the maximum relative error of the measured frequency modulation index m f is 3.2%, the maximum measurement error of the carrier signal frequency of the single-frequency modulated (modulation signal is a sine wave) FM wave is almost 0%, and the error of the carrier frequency of the unmodulated single-frequency continuous carrier signal is almost 0%.

[0173] Tables 1 and 2 are the results of multiple actual measurements of the automatic identification of the modulation type of the radio signal and the automatic measurement of the modulation parameters.

[0174] Table 1

[0175]

[0176] Table 2

[0177]

[0178] Table 1 is the automatic measurement result of the liquid crystal screen of the measurement system when the input signal to be measured is a single-frequency modulated (modulation signal is a sine wave) AM wave with a carrier frequency of 20 MHz and a modulation index of 0.2, 0.4, 0.6, 0.8 and 1, respectively, and the corresponding modulation signal frequency is 2 kHz, 3.5 kHz and 5 kHz, respectively. The measurement result includes the carrier frequency and the modulation index, and the maximum parameter error of the AM wave with the same parameters measured for 10 times in succession. The measurement result shows that the system correctly judges the type of the input AM wave to be measured, and the maximum relative error of the AM wave demodulation signal frequency is 2.4% when the same parameters are measured for 10 times in succession, and the maximum relative error of the measured modulation index m a is 8.0%.

[0179] Table 2 is the automatic measurement result of the liquid crystal screen of the measurement system when the input signal to be measured is a single-frequency modulated (modulation signal is a sine wave) FM wave with a carrier frequency of 20 MHz and a frequency modulation index of 1, 2, 3.5, 5 and 6, respectively, and the corresponding modulation signal frequency is 3 kHz, 6 kHz and 10 kHz, respectively. The measurement result includes the carrier frequency, the frequency modulation index, and the maximum parameter error of the FM wave with the same parameters measured for 10 times in succession. The measurement result shows that the system correctly judges the type of the input FM wave to be measured, and the maximum relative error of the FM wave demodulation signal frequency is 2.0% when the same parameters are measured for 10 times in succession, and the maximum relative error of the measured frequency modulation index m f is 3.2%.

[0180] The technical solutions of the present application are not limited to the above-mentioned embodiments, and any technical solution obtained by equivalent replacement falls within the scope of the present application.

Claims

1. A system for automatic measurement of modulation parameters of a radio signal, characterized in that It comprises: The local oscillator signal source circuit module outputs the local oscillator signal containing single frequency sine wave signal and continuous frequency sweep sine wave signal based on DDS; The envelope detection circuit module is used for demodulating single frequency modulation ordinary amplitude modulation wave signal; The stereo frequency modulation demodulation circuit module is used for demodulating single frequency modulation frequency modulation wave signal with fixed carrier frequency, the high-speed electronic switch circuit module is used for switching the input amplitude modulation wave demodulation channel or the frequency modulation wave demodulation channel of the to-be-tested signal, switching the demodulated amplitude modulation wave signal or frequency modulation wave signal into the output channel, and switching the baseband signal after the to-be-tested radio signal mixing or the demodulated signal of the amplitude modulation wave signal or frequency modulation wave signal in the output channel for ADC sampling, The active mixer circuit module comprises a mixer, which completes the mixing of the input to-be-tested radio signal and the local oscillator signal, and shifts the frequency spectrum and carrier frequency of the input to-be-tested radio signal; The passive high-pass filter circuit module is used as a frequency selection filter after the mixing of the input to-be-tested single frequency modulation frequency modulation wave signal, and the selected up-converted frequency modulation wave signal is input into the stereo frequency modulation demodulation module; The single-chip microcomputer controls the DDS to generate the local oscillator signal, controls the high-speed electronic switch to perform ADC sampling and select the amplitude modulation wave demodulation channel or the frequency modulation wave demodulation channel, calculates the modulation parameters including frequency, frequency spectrum, amplitude modulation index of the amplitude modulation signal and frequency modulation index of the frequency modulation wave, judges the modulation type of the to-be-tested signal, and tracks and measures the carrier frequency of the single frequency modulation frequency modulation wave and the unmodulated single frequency continuous carrier signal; The specific process that the single-chip microcomputer judges the modulation type of the to-be-tested signal and tracks and measures the carrier frequency of the single frequency modulation frequency modulation wave and the unmodulated single frequency continuous carrier signal is as follows: The to-be-tested radio signal is selected to first enter the amplitude modulation wave demodulation channel through the electronic switch, the output of the envelope detection circuit is input into the single-chip microcomputer for sampling, if the sampled signal is a standard single frequency sine wave periodic signal, it is judged that the input signal is a single frequency modulation ordinary amplitude modulation wave; If it is not a sine wave, the to-be-tested signal is input into the frequency modulation wave demodulation channel through the electronic switch again, the frequency modulation wave type is judged and the carrier frequency is measured; During the frequency sweep of the local oscillator signal, the single-chip microcomputer performs FFT transformation on the sampling signal corresponding to each frequency point of the local oscillator signal, obtains the frequency spectrum information of the down-converted to-be-tested radio signal, and then uses the single-chip microcomputer to sample the down-converted signal, performs FFT transformation analysis on the main characteristics of the frequency spectrum, if the frequency spectrum obtained by FFT transformation of the sampling signal contains at least two frequency spectrum components near zero frequency corresponding to a certain frequency of the local oscillator signal during the frequency sweep, it is judged that the to-be-tested radio signal is a single frequency modulation frequency modulation wave, according to the frequency spectrum characteristic analysis, when the frequency of the local oscillator signal is the same as the carrier frequency of the to-be-tested frequency modulation wave, the corresponding local oscillator signal frequency f0 is recorded, f0 is the carrier frequency of the to-be-tested frequency modulation wave; If after a complete round of frequency sweep of the local oscillator signal, the frequency spectrum obtained by FFT transformation of the sampling signal does not have at least two frequency components with large amplitudes near zero frequency, it can be judged that the to-be-tested signal is not a frequency modulation wave, and the to-be-tested signal is an unmodulated single frequency continuous carrier signal.

2. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The intermediate frequency amplifier circuit module amplifies the input single-frequency modulated common amplitude modulation wave signal to be tested, so that the amplitude of the input amplitude modulation wave signal to be tested reaches the input level requirement of the envelope detection module.

3. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The first active low-pass filter circuit is used as a filter of the baseband signal obtained by down-converting the externally input single-frequency modulated frequency modulation wave signal to be tested through the frequency mixer and the local oscillator signal.

4. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The second active low-pass filter circuit module filters the modulated signal output by the envelope detection module and the stereo frequency modulation demodulation module to filter out high-frequency components and noise.

5. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The low-frequency amplifier circuit module amplifies the baseband signal after down-conversion of the frequency mixer and the modulated signal output by the stereo frequency modulation demodulation circuit module.

6. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The superheterodyne structure is used to shift the spectrum of the signal to be tested to the baseband, and the single-chip microcomputer is used to sample the down-converted signal and perform FFT transformation to obtain the spectral characteristics of the signal.

7. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The single-chip computer calculates the amplitude modulation index m of the single-tone modulation common amplitude modulation wave a The specific process is: 1) Normalized amplitude modulation index m a Calculation: The single-frequency modulated AM wave is described by the following mathematical expression: wherein is called the amplitude modulation index or amplitude modulation depth, k a denotes the sensitivity of the amplitude modulation, V0denotes the unmodulated carrier amplitude, V Ω denotes the amplitude of the modulation signal; According to equation (1), it can be deduced that V max and V min respectively represent the maximum and minimum values of the amplitude modulation wave envelope; The voltage transfer coefficient of the envelope detection circuit is basically unchanged, and the voltage transfer coefficient K of the envelope detection circuit is measured in advance d The single-chip microcomputer is used for sampling and measuring the demodulation waveform amplitude U Ω According to formula (3), the envelope amplitude m of the general amplitude modulation wave is converted a Vim, the amplitude modulation index m of the to-be-measured amplitude modulation wave can be calculated a ; where K d is the voltage transfer coefficient of the detector, U Ω is the output voltage of the envelope detector, m a is the modulation index, U i is the amplitude of the carrier voltage.

8. The system for automatic measurement of modulation parameters of radio signals according to claim 1, characterized in that The single-chip computer calculates the frequency modulation index m of the measured frequency modulation wave f , the maximum frequency deviation Δf m Specifically includes the following steps: Step 1) According to the characteristic that the slope of the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is basically unchanged in the linear region, the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is measured in advance; Step 2) Calculate the slope of the frequency discrimination S curve, that is, the frequency discrimination sensitivity k of the stereo frequency modulation demodulation circuit f , the single-chip microcomputer samples and measures the voltage amplitude V of the output waveform of the frequency discriminator m , the frequency f of the demodulation waveform, that is, the modulated signal, is calculated by FFT m , according to the frequency discrimination sensitivity k f , the maximum frequency deviation Δf of the corresponding to-be-measured frequency modulation wave is calculated by formula (4) m ; The frequency modulation index m corresponding to the frequency modulation wave to be measured is calculated according to formula (5) f ;

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