Main characteristics of finished product】
1. Frequency range: 525~1605kHz
2. Power supply voltage: 6V
3. Circuit board size: 78mmx85mm (length × width)
4. Transmitting distance: superheterodyne medium wave radio is about 1 meter, direct-type medium wave radio is about 0.5 meter
【Features】
1. The circuit is simple. It is only composed of commonly used triodes and resistance-capacitance components, without audio transformer, easy to make;
2. The sound quality is good. Within the rated transmission distance, the sound quality is close to FM broadcasting, and the signal-to-noise ratio is good, especially the effect of receiving with a repeater is not much different from that of direct broadcasting of the modulated signal;
3. No external antenna is needed (medium wave needs tens of meters), and the receiver is completely affected by the magnetic field leaked by the magnetic rod, which is easy to implement, but the transmission distance is relatively short;
4. There are many interfaces, designed with various levels of transistors, quiescent current test jumpers, and external power sockets, which are easy to use and expand functions;
5. It can be used with an external power supply, or it can be used independently by adding a battery pack module (battery power supply board).
【product description】
1. This kit uses fully discrete circuits, which is especially suitable for students to learn working principles, practice production and test;
2. Variable capacitors use frequency modulation and amplitude modulation quadruple variable capacitors, and connect two amplitude modulation couplings in parallel to obtain sufficient capacity. The quadruple is better than the common 223P AM double-connected variable capacitor, and feels better;
3. The circuit board base is made of glass fiber material, the thickness measured is about 1.5~1.6mm, the single-sided green/butter white lettering, the pad is sprayed with tin, and can be directly welded without grinding;
4. The circuit board obtained by the buyer may be slightly different from the sample in the picture, mainly due to the change of component position and the same circuit structure. This product has been modified and perfected n times from trial-produced samples to products sold (mainly to modify the wiring of the circuit board), and is still in continuous improvement. Usually minor insubstantial modifications, such as slight movement of component positions and minor wiring adjustments will not change the version number, and will not re-photograph and upload, hereby declare;
5. The manual contains circuit schematic diagrams and circuit board diagrams, as well as debugging methods and experience under amateur conditions. If you need more information and professional debugging methods, please download or refer to relevant professional books on the Internet;
6. The transmitter board is equipped with a 3.5mm headphone signal line, and the battery-powered board is optional and non-essential, without batteries.
【Effect】
This transmitter works well within the effective distance (0.5~1 meters), and the sound fidelity is high, especially with direct-type radios (such as our store’s 636 and 68-1 single tube machines) with our self-made high resistance When listening to the earphone, the sound quality is not much different from that of the player directly.
Plug the external 6V DC power supply (internal positive and external negative) into the CZ1 socket on the board, or plug the 6V battery pack connector into the Battery interface, paying attention to the positive and negative poles.
Insert the signal cable into the CZ2 socket of the circuit board and connect it to the modulation signal source. The signal source can be a mobile phone, a player, etc. It is recommended to use a player, because the mobile phone has strong interference to the medium wave radio.
Turn the potentiometer knob to turn it on. The effect of this potentiometer is similar to the volume potentiometer of a radio.
Turn on the radio, search for the transmitter’s signal, and then listen. You can also reverse the operation, adjust the receiving frequency of the radio to a position where there is no radio station, and then turn the dial of the transmitter to change the transmit frequency until the radio broadcasts the signal from the transmitter.
【Restrictions on Use】
1. This product has a good effect only in the range of the desktop. When the radio is too far away from the transmitter (more than 1 meter), the effect will be severely reduced, which is manifested as a low sound signal-to-noise ratio deterioration;
2. Increasing the power supply voltage can increase the waveform amplitude a lot, but the actual usable transmission distance does not change much;
3. The potentiometer of the transmitter controls the modulation degree. If the modulation is too large, the demodulation of the radio will be distorted, and the waveform of the transmitter itself will become worse. The correct usage is to sum up a suitable position after multiple uses to make the modulation degree as much as possible It is large and can ensure the sound quality as much as possible, just turn to this position every time you use it, don’t use it as a radio volume potentiometer to frequently adjust it;
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