Long-distance FM transmitter circuit diagram made of high-frequency triode

As shown in the figure, it is a long-distance FM transmitter circuit made of ordinary triode 3DA87C . This circuit is also an ordinary three-point oscillator circuit. This long-distance transmitter circuit uses high current transmission and can reach 1KM in open areas. It is assembled and tested according to the schematic diagram. The triode The magnification factor marked with the blue dot should be greater than 80 times. However, it was found in the experiment that its frequency does not fall within the normal FM band of 88-108 MHZ. Instead, no matter how the capacitance and inductance are adjusted, it is lower than 88 MHZ. At a frequency of about seventy MHZ, the TESUN radio with the TV sound receiving function can receive normally. The fT cutoff frequency parameter value of the transistor is not enough, so that the oscillation frequency cannot be raised.

In order to increase the transmitting distance and make the frequency fall within the receiving range of normal FM radio, we had to find other high-frequency triodes, and use D40, C1971, and C1972 as high-frequency oscillation or power amplifier circuits, with their high-power output to increase the launch distance, but this type of high-frequency triode is difficult to buy on the market, and even if you can buy it, most of it is fake and cannot be used. Later, I found C3355. The cut-off frequency of this triode is several thousand MHZ, and its power is 600MW, which is enough for FM band. Then I made some improvements to the circuit, and I can easily create a long-distance FM transmitter circuit .

Component selection: Capacitors C2, C3, and C4 are all high-frequency ceramic capacitors, and Ct is a high-frequency semi-adjustable capacitor of 5/25P. It can also be replaced with a high-frequency ceramic capacitor of the same value after testing with a digital multimeter after debugging. The capacitor , L, is an enameled wire with a diameter of 0.9, wound around 6 turns on an 8mm round tube, and then pulled apart about 2CM, with a tap in the middle. The transmitting antenna is replaced by a TV antenna or a wire of the same length.

After actual debugging to achieve the best transmit power, the longest distance is no less than 500 meters.