Dual-mode medium wave transmitting apparatus and method compatible with analog and digital modulation

Abstract

The application discloses a dual-mode medium wave transmitting device and method compatible with analog and digital modulation, and the medium wave transmitting device comprises a power supply and indication unit, a core oscillation unit, a biasing and control unit and a signal input unit; the core oscillation unit comprises a triode Q1, a medium wave magnetic rod antenna coil H1, a first feedback capacitor C2 and a second feedback capacitor C1, wherein the medium wave magnetic rod antenna coil H1, the first feedback capacitor C2 and the second feedback capacitor C1 constitute an inductive three-point oscillation loop; the biasing and control unit comprises a base biasing resistor R1, a two-way switching switch SW1, a current-limiting resistor R2 and an external control interface, the triode Q1 is connected with the two-way switching switch SW1, a first fixed end of the two-way switching switch SW1 is connected with a power supply VCC, and a second fixed end is connected with the external control interface through the current-limiting resistor R2. The device can meet the requirements of radio analog modulation principle demonstration and digital communication experiment, and greatly improves the practicability and teaching value of the device.

Description

Technical Field

[0001] This invention relates to the field of medium-wave transmitter technology. Specifically, it relates to a dual-mode medium-wave transmitting device and method compatible with both analog and digital modulation. Background Technology

[0002] Medium wave transmitters are widely used in the field of radio communication. In amateur radio, electronic education and simple communication experiments, medium wave transmitting circuits built with a single transistor or a small number of transistors are classic designs that have both teaching and practical value. They are usually based on a capacitor three-point or inductor three-point oscillator circuit as the core architecture to realize the basic radio signal transmission function.

[0003] Currently, while simple medium-wave transmitting circuits of the same level for this field are simple in structure and easy to build, and can meet the needs of basic radio principle demonstrations and simple communication experiments, they have obvious shortcomings in functional integration, ease of operation, and equipment compatibility.

[0004] 1. Limited functionality, supporting only a single mode of pure analog amplitude modulation (AM) or pure digital amplitude shift keying (ASK), making it impossible to complete both analog and digital communication experiments on a single circuit.

[0005] 2. The mode switching is cumbersome, requiring hardware operations such as plugging and unplugging jumpers, replacing components, and modifying circuit structure, which is prone to errors and affects the continuity of teaching demonstrations.

[0006] 3. Poor adaptability: Some digital ASK circuits require additional peripheral circuits such as level conversion and switches to be able to directly and safely interface with the digital I / O ports of commonly used microcontrollers such as Arduino, which increases the complexity and cost of the circuit.

[0007] In summary, while existing medium-wave transmitting circuits possess basic experimental demonstration functions, there is still significant room for improvement in terms of functional integration, ease of experimental operation, and compatibility with modern digital control equipment. Consequently, they are insufficient to meet the diverse, convenient, and intelligent needs of current electronic teaching and amateur experiments. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to provide a dual-mode medium-wave transmitting device and method compatible with analog and digital modulation. The device creatively connects the power supply terminal of the base bias resistor of the transistor to a dual-channel selection switch, and switches the bias circuit between "fixed power supply" and "controlled signal source" through the dual-channel selection switch, thereby realizing the essential switching of two communication modes with one circuit.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] A dual-mode medium-wave transmitter compatible with analog and digital modulation includes a power supply and indication unit, a core oscillation unit, a bias and control unit, and a signal input unit.

[0011] The core oscillation unit includes a transistor Q1, a medium-wave ferrite rod antenna coil H1, a first feedback capacitor C2, and a second feedback capacitor C1. The collector of transistor Q1 is connected to the center tap of the medium-wave ferrite rod antenna coil H1. One end of the medium-wave ferrite rod antenna coil H1 is connected to the emitter of transistor Q1 through the first feedback capacitor C2. The other end of the medium-wave ferrite rod antenna coil H1 is grounded. The emitter of transistor Q1 is grounded through the second feedback capacitor C1. The medium-wave ferrite rod antenna coil H1, the first feedback capacitor C2, and the second feedback capacitor C1 constitute an inductive three-point oscillation circuit.

[0012] The bias and control unit includes a base bias resistor R1, a dual-channel switch SW1, a current-limiting resistor R2, and an external control interface. The base of transistor Q1 is connected to the common terminal of the dual-channel switch SW1 through the base bias resistor R1. The first fixed terminal of the dual-channel switch SW1 is connected to the power supply VCC, and the second fixed terminal is connected to the external control interface through the current-limiting resistor R2.

[0013] The aforementioned dual-mode medium-wave transmitter compatible with analog and digital modulation includes an analog audio input circuit and a digital signal input circuit in its signal input unit. The analog audio input circuit is connected to the base of transistor Q1, and the digital signal input circuit includes the external control interface.

[0014] In the aforementioned dual-mode medium-wave transmitter compatible with analog and digital modulation, when the dual-channel switching switch SW1 is switched to the first fixed terminal, the base bias resistor R1 is connected to the power supply VCC, providing a static operating point for the transistor Q1, and the transmitter is in analog modulation mode.

[0015] When the dual-channel switching switch SW1 is switched to the second fixed terminal, the base bias of transistor Q1 is controlled by the digital signal input from the external control interface, and the transmitting device is in digital modulation mode.

[0016] In the aforementioned dual-mode medium-wave transmitter compatible with analog and digital modulation, when the transmitter is in digital modulation mode, the digital control signal acts on the base of transistor Q1 through the current-limiting resistor R2. When the digital control signal is high, it provides bias to transistor Q1, and the circuit starts oscillating to transmit the carrier wave. When the digital control signal is low, the bias of transistor Q1 is cut off, causing the circuit to stop oscillating, thereby realizing amplitude shift keying digital modulation.

[0017] The aforementioned dual-mode medium-wave transmitter compatible with analog and digital modulation includes an analog audio input circuit comprising a coupling capacitor and an audio potentiometer U1. The audio signal source is connected to the base of transistor Q1 in sequence through the coupling capacitor and the audio potentiometer U1 to achieve amplitude modulation of the high-frequency carrier.

[0018] The aforementioned dual-mode medium-wave transmitter compatible with analog and digital modulation includes a power supply and indicator unit comprising a power supply VCC, a power supply filter capacitor C4, and a light-emitting diode (LED). The power supply VCC is grounded to GND through the power supply filter capacitor C4, and the LED is connected in parallel between the power supply VCC and GND.

[0019] In the aforementioned dual-mode medium-wave transmitter compatible with analog and digital modulation, the transistor Q1 is a 9018 NPN transistor, the power supply filter capacitor C4 has a capacitance of 10uF, the first feedback capacitor C2 has a capacitance of 10nF, the second feedback capacitor C1 has a capacitance of 2.2nF, and the base bias resistor R1 has a resistance of 15kΩ.

[0020] The aforementioned dual-mode medium-wave transmitter compatible with both analog and digital modulation has an inductive three-point oscillation circuit operating in the medium-wave frequency band of 530kHz-1600kHz.

[0021] The aforementioned dual-mode medium-wave transmitter compatible with both analog and digital modulation has an external control interface that is a digital I / O pin of a microcontroller.

[0022] A dual-mode medium-wave transmission method compatible with analog and digital modulation is implemented based on the aforementioned medium-wave transmission device, including an analog amplitude modulation working mode and a digital keying working mode, with the two modulation modes being switched via a dual-channel switch SW1;

[0023] The specific working process of the analog amplitude modulation working mode is as follows: First, the dual-channel switch SW1 is switched to the first fixed terminal connected to the power supply VCC. The power supply VCC establishes a stable base bias current for the transistor Q1 through the base bias resistor R1. The core oscillation unit starts working and generates a medium-wave constant amplitude carrier signal of a specific frequency. Then, the audio signal source is connected to the analog audio input interface. The audio signal is sent to the base of the transistor Q1 through the coupling capacitor, so that the base-emitter junction voltage of the transistor Q1 changes with the audio waveform, thereby changing its amplification capability and the energy supply amplitude of the oscillation circuit. This causes the high-frequency carrier amplitude radiated by the medium-wave ferrite rod antenna coil H1 to follow the change of the audio signal, completing the modulation of the analog amplitude modulation working mode and transmitting it outward.

[0024] The specific working process of the digital keying mode is as follows: First, switch the dual-channel switch SW1 to the second fixed terminal connected to the external control interface. The base bias circuit of transistor Q1 is connected to the external control interface, and its working state is controlled by the external digital signal. Then, connect the digital output pin of the external microcontroller to the digital signal input interface. When the digital output pin outputs a high level, the high level provides bias current to transistor Q1 through the current limiting resistor R2, the oscillation circuit works, and the medium-wave ferrite rod antenna coil H1 radiates the carrier wave, representing the digital signal 1. When the digital output pin outputs a low level, transistor Q1 is cut off, the oscillation circuit stops oscillating, there is no carrier radiation, representing the digital signal 0. By controlling the digital output pin to output a high and low level sequence, the digital signal after digital keying modulation is transmitted.

[0025] The technical solution of the present invention achieves the following beneficial technical effects:

[0026] This application uses an NPN transistor as the core oscillation and amplification device, paired with an inductive three-point oscillation circuit and a corresponding dual-channel switch, to simultaneously realize both analog amplitude modulation (AM) and digital keying (ASK) communication modes without the need to build separate analog and digital transmission circuits. A single device can complete the broadcast transmission of analog signals and the transmission of digital signals such as switching signals and coded data, meeting the needs of both analog radio modulation principle demonstrations and digital communication experiments. It effectively solves the problem of traditional simple circuits having limited functionality and being unable to handle both analog and digital experiments, significantly improving the device's practicality and educational value.

[0027] This application utilizes a dual-channel switch to switch between AM and ASK modes. The switching is achieved simply by toggling the switch, eliminating the need for hardware operations such as plugging / unplugging jumpers, replacing components, or modifying circuit wiring. The switching process is intuitive and quick, avoiding the cumbersome and error-prone operations associated with traditional circuits requiring hardware modifications. This ensures the continuity and smoothness of electronic teaching demonstrations and amateur experiments, lowering the barrier to entry for experimental operations, making it particularly suitable for teaching scenarios and beginner radio enthusiasts.

[0028] The dedicated digital modulation mode interface of this application can directly interface with the digital I / O pins of commonly used microcontrollers such as Arduino. The digital signal, after passing through a current-limiting resistor, directly controls the base bias of the transistor, realizing the start and stop of oscillation circuitry, without the need for additional level conversion circuits, switch driver circuits, or other peripheral modules. This simplifies the circuit structure, reduces hardware costs, improves the compatibility of the device with modern digital control equipment, and facilitates users to transmit encoded data through programming, expanding the application scenarios of simple medium-wave transmitters.

[0029] This application features a simple overall circuit structure, a small number of components, and a compact size, resulting in extremely low manufacturing and debugging costs, making it suitable for mass production and use in electronic teaching experiments. Furthermore, it employs a classic three-point inductive oscillator circuit as its core, ensuring stable circuit operation and high carrier signal purity. It can stably output within the 530-1600kHz mid-wave frequency band, meeting the signal quality requirements for amateur experiments and principle demonstrations. Attached Figure Description

[0030] Figure 1 A schematic diagram of the dual-mode medium-wave transmitting device of the present invention;

[0031] Figure 2 The schematic diagram of the dual-mode medium-wave transmitting device of the present invention. Detailed Implementation

[0032] Example 1: This example discloses a dual-mode medium-wave transmitter compatible with both analog and digital modulation, such as... Figure 1 and Figure 2 As shown, it includes a power supply and indication unit, a core oscillation unit, a bias and control unit, and a signal input unit;

[0033] The core oscillation unit includes a transistor Q1, a medium-wave ferrite rod antenna coil H1, a first feedback capacitor C2, and a second feedback capacitor C1. The collector of transistor Q1 is connected to the center tap of the medium-wave ferrite rod antenna coil H1. One end of the medium-wave ferrite rod antenna coil H1 is connected to the emitter of transistor Q1 through the first feedback capacitor C2. The other end of the medium-wave ferrite rod antenna coil H1 is grounded, and the emitter of transistor Q1 is grounded through the second feedback capacitor C1. The medium-wave ferrite rod antenna coil H1, the first feedback capacitor C2, and the second feedback capacitor C1 constitute an inductive three-point oscillation circuit. The operating frequency band of the inductive three-point oscillation circuit is the medium-wave band of 530kHz-1600kHz.

[0034] The bias and control unit includes a base bias resistor R1, a dual-channel switch SW1, a current-limiting resistor R2, and an external control interface. The base of transistor Q1 is connected to the common terminal of the dual-channel switch SW1 through the base bias resistor R1. The first fixed terminal of the dual-channel switch SW1 is connected to the power supply VCC, and the second fixed terminal is connected to the external control interface through the current-limiting resistor R2. The external control interface is a digital I / O pin of a microcontroller (such as Arduino).

[0035] Specifically, when the dual-channel switching switch SW1 is switched to the first fixed terminal, the base bias resistor R1 is connected to the power supply VCC, providing a static operating point for the transistor Q1, and the transmitting device is in analog modulation mode.

[0036] When the dual-channel switching switch SW1 is switched to the second fixed terminal, the base bias of transistor Q1 is controlled by the digital signal input from the external control interface, and the transmitting device is in digital modulation mode.

[0037] The signal input unit includes an analog audio input circuit and a digital signal input circuit. The analog audio input circuit is connected to the base of transistor Q1, and the digital signal input circuit includes the external control interface. The analog audio input circuit includes a coupling capacitor and an audio potentiometer U1. The audio signal source is connected to the base of transistor Q1 in sequence through the coupling capacitor and the audio potentiometer U1 to achieve amplitude modulation of the high-frequency carrier wave (the coupling capacitor of the analog audio input circuit in this application is not shown in the schematic diagram, but needs to be provided by the manufacturer in actual production applications).

[0038] When the transmitter is in digital modulation mode, the digital control signal acts on the base of transistor Q1 through the current limiting resistor R2. When the digital control signal is high, it provides bias to transistor Q1, and the circuit starts oscillating to transmit the carrier wave. When the digital control signal is low, the bias of transistor Q1 is cut off, causing the circuit to stop oscillating, thereby realizing amplitude shift keying digital modulation.

[0039] The power supply and indicator unit includes a power supply VCC, a power supply filter capacitor C4, and a light-emitting diode. The power supply VCC is grounded to GND through the power supply filter capacitor C4, and the light-emitting diode is connected in parallel between the power supply VCC and GND.

[0040] The transistor Q1 is a 9018 NPN transistor, the power supply filter capacitor C4 has a capacitance of 10uF, the first feedback capacitor C2 has a capacitance of 10nF, the second feedback capacitor C1 has a capacitance of 2.2nF, and the base bias resistor R1 has a resistance of 15kΩ.

[0041] This application boasts high functional integration and outstanding experimental cost-effectiveness. Using a minimal set of components (a transistor, a medium-wave ferrite rod antenna coil, and several resistors and capacitors), it achieves transmission functions for both AM and ASK basic radio modulation methods. Users can complete comparative experiments from analog to digital communication without building two separate circuits, significantly improving the functional density and cost-effectiveness of teaching kits or experimental modules.

[0042] The experimental process described in this application is smooth and highly demonstrative. Mode switching is completed instantly with a single physical switch, without the need to reconnect cables or adjust components. This allows for the smooth sequential demonstration of the "Medium Wave Broadcast Simulation" and "Wireless Digital Encoding Transmission" experiments in the classroom or laboratory, enhancing the continuity and impact of the teaching demonstration.

[0043] This application significantly reduces the access difficulty of digital modulation experiments, providing a standard interface for ASK modulation to directly connect to a general-purpose microcontroller. Experimenters do not need to have an in-depth understanding of the details of radio frequency control; they only need to write simple digital output code to immediately observe the phenomenon of controlled carrier switching and its effect on the receiver. This makes the abstract principles of digital communication intuitive and easy to understand, making it particularly suitable for beginners.

[0044] This application retains the core advantages of simple circuits. While adding practical functions, it still maintains the advantages of traditional simple circuits, such as clear circuit structure, low component cost, and ease of manual soldering, thus continuing its core value as a "hands-on learning tool".

[0045] Example 2 discloses a dual-mode medium-wave transmission method compatible with analog and digital modulation, implemented based on the medium-wave transmission device described in Example 1, including an analog amplitude modulation working mode and a digital keying working mode, with the two modulation modes switched by a dual-channel switching switch SW1;

[0046] The specific working process of the analog amplitude modulation working mode is as follows:

[0047] 1. Mode preparation: Set the dual-channel switch SW1 to the first fixed terminal connected to the power supply VCC. At this time, the power supply VCC establishes a stable base bias current for the transistor Q1 through the base bias resistor R1. The transistor Q1 enters the working state, and the core oscillation unit starts to oscillate under the drive of the bias current. The inductive three-point oscillation circuit composed of the medium-wave ferrite rod antenna coil H1, the first feedback capacitor C2 and the second feedback capacitor C1 generates a medium-wave constant amplitude carrier signal of a specific frequency.

[0048] 2. Signal Modulation and Transmission: Connect the microphone amplifier circuit, music player and other audio signal sources to the device's analog audio input interface. The audio signal is coupled through the coupling capacitor and sent to the base of transistor Q1. Changes in the waveform of the audio signal will directly cause synchronous changes in the base-emitter junction voltage of transistor Q1, thereby causing the transconductance and amplification capability of transistor Q1 to change with the audio waveform.

[0049] The change in the amplification capability of transistor Q1 will cause the energy supply amplitude of the oscillation circuit to fluctuate accordingly. Ultimately, the high-frequency carrier radiated by the medium-wave ferrite rod antenna coil H1 will strictly follow the amplitude change of the input audio signal, completing the analog amplitude modulation (AM) process. The amplitude-modulated medium-wave signal is radiated outward through the ferrite rod antenna to realize the wireless transmission of analog voice and music signals.

[0050] The specific working process of the digital keying working mode is as follows:

[0051] 1. Mode preparation: Set the dual-channel switch SW1 to the second fixed terminal connected to the external control interface. At this time, the base bias circuit of transistor Q1 is connected to the external digital control interface. The working state of transistor Q1 is no longer biased by the power supply VCC, but is completely controlled by the externally input digital signal.

[0052] 2. Digital Modulation and Transmission: Connect the digital I / O output pins of microcontrollers such as Arduino to the digital signal input interface of the device. The microcontroller program then controls these digital pins to output high and low level signals.

[0053] When the digital pin outputs a high level, the high-level signal provides the base bias current required for the transistor Q1 to conduct through the current-limiting resistor R2. When the transistor Q1 conducts, the core oscillation circuit starts oscillating normally, and the medium-wave ferrite rod antenna coil H1 radiates the medium-wave carrier wave outward. This state corresponds to the digital signal "1".

[0054] When the digital pin outputs a low level, transistor Q1 is cut off due to the lack of base bias current, the oscillation circuit loses its energy supply, the oscillation stops, and the ferrite rod antenna has no carrier radiation. This state corresponds to the digital signal "0".

[0055] By controlling the microcontroller to output specific high and low level sequences, such as Manchester encoding, carrier on / off keying can be achieved, ASK digital modulation can be completed, and the encoded digital signal can be transmitted through the medium wave band.

[0056] The above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A dual-mode medium-wave transmitter compatible with both analog and digital modulation, characterized in that, It includes a power supply and indication unit, a core oscillation unit, a bias and control unit, and a signal input unit; The core oscillation unit includes a transistor Q1, a medium-wave ferrite rod antenna coil H1, a first feedback capacitor C2, and a second feedback capacitor C1. The collector of transistor Q1 is connected to the center tap of the medium-wave ferrite rod antenna coil H1. One end of the medium-wave ferrite rod antenna coil H1 is connected to the emitter of transistor Q1 through the first feedback capacitor C2. The other end of the medium-wave ferrite rod antenna coil H1 is grounded. The emitter of transistor Q1 is grounded through the second feedback capacitor C1. The medium-wave ferrite rod antenna coil H1, the first feedback capacitor C2, and the second feedback capacitor C1 constitute an inductive three-point oscillation circuit. The bias and control unit includes a base bias resistor R1, a dual-channel switch SW1, a current-limiting resistor R2, and an external control interface. The base of transistor Q1 is connected to the common terminal of the dual-channel switch SW1 through the base bias resistor R1. The first fixed terminal of the dual-channel switch SW1 is connected to the power supply VCC, and the second fixed terminal is connected to the external control interface through the current-limiting resistor R2.

2. The dual-mode medium-wave transmitter compatible with analog and digital modulation according to claim 1, characterized in that, The signal input unit includes an analog audio input circuit and a digital signal input circuit. The analog audio input circuit is connected to the base of transistor Q1, and the digital signal input circuit includes the external control interface.

3. The dual-mode medium-wave transmitting device compatible with analog and digital modulation according to claim 2, characterized in that, When the dual-channel switching switch SW1 is switched to the first fixed terminal, the base bias resistor R1 is connected to the power supply VCC, providing a static operating point for the transistor Q1, and the transmitting device is in analog modulation mode. When the dual-channel switching switch SW1 is switched to the second fixed terminal, the base bias of transistor Q1 is controlled by the digital signal input from the external control interface, and the transmitting device is in digital modulation mode.

4. The dual-mode medium-wave transmitting device compatible with analog and digital modulation according to claim 3, characterized in that, When the transmitter is in digital modulation mode, the digital control signal acts on the base of transistor Q1 through the current limiting resistor R2. When the digital control signal is high, it provides bias to transistor Q1, and the circuit starts oscillating to transmit the carrier wave. When the digital control signal is low, the bias of transistor Q1 is cut off, causing the circuit to stop oscillating, thereby realizing amplitude shift keying digital modulation.

5. The dual-mode medium-wave transmitting device compatible with analog and digital modulation according to claim 2, characterized in that, The analog audio input circuit includes a coupling capacitor and an audio potentiometer U1. The audio signal source is connected to the base of transistor Q1 in sequence through the coupling capacitor and the audio potentiometer U1 to achieve amplitude modulation of the high-frequency carrier.

6. The dual-mode medium-wave transmitter compatible with analog and digital modulation according to claim 1, characterized in that, The power supply and indicator unit includes a power supply VCC, a power supply filter capacitor C4, and a light-emitting diode. The power supply VCC is grounded to GND through the power supply filter capacitor C4, and the light-emitting diode is connected in parallel between the power supply VCC and GND.

7. The dual-mode medium-wave transmitting device compatible with analog and digital modulation according to claim 6, characterized in that, The transistor Q1 is a 9018 NPN transistor, the power supply filter capacitor C4 has a capacitance of 10uF, the first feedback capacitor C2 has a capacitance of 10nF, the second feedback capacitor C1 has a capacitance of 2.2nF, and the base bias resistor R1 has a resistance of 15kΩ.

8. The dual-mode medium-wave transmitter compatible with analog and digital modulation according to claim 1, characterized in that, The operating frequency band of the inductive three-point oscillation circuit is the medium wave band of 530kHz-1600kHz.

9. The dual-mode medium-wave transmitter compatible with analog and digital modulation according to claim 1, characterized in that, The external control interface is the digital I / O pin of the microcontroller.

10. A dual-mode medium-wave transmission method compatible with analog and digital modulation, implemented based on the dual-mode medium-wave transmission device compatible with analog and digital modulation as described in any one of claims 1-9, characterized in that, It includes analog amplitude modulation (AM) mode and digital keying (DKP) mode, which can be switched via a dual-channel switch SW1. The specific working process of the analog amplitude modulation working mode is as follows: First, the dual-channel switch SW1 is switched to the first fixed terminal connected to the power supply VCC. The power supply VCC establishes a stable base bias current for the transistor Q1 through the base bias resistor R1. The core oscillation unit starts working and generates a medium-wave constant amplitude carrier signal of a specific frequency. Then, the audio signal source is connected to the analog audio input interface. The audio signal is sent to the base of the transistor Q1 through the coupling capacitor, so that the base-emitter junction voltage of the transistor Q1 changes with the audio waveform, thereby changing its amplification capability and the energy supply amplitude of the oscillation circuit. This causes the high-frequency carrier amplitude radiated by the medium-wave ferrite rod antenna coil H1 to follow the change of the audio signal, completing the modulation of the analog amplitude modulation working mode and transmitting it outward. The specific working process of the digital keying mode is as follows: First, switch the dual-channel switch SW1 to the second fixed terminal connected to the external control interface. The base bias circuit of transistor Q1 is connected to the external control interface, and its working state is controlled by the external digital signal. Then, connect the digital output pin of the external microcontroller to the digital signal input interface. When the digital output pin outputs a high level, the high level provides bias current to transistor Q1 through the current limiting resistor R2, the oscillation circuit works, and the medium-wave ferrite rod antenna coil H1 radiates the carrier wave, representing the digital signal 1. When the digital output pin outputs a low level, transistor Q1 is cut off, the oscillation circuit stops oscillating, there is no carrier radiation, representing the digital signal 0. By controlling the digital output pin to output a high and low level sequence, the digital signal after digital keying modulation is transmitted.

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