Use 3DA87C DIY make the FM broadcast transmitter circuit

The figure is from the introduction of an electronic magazine on a regular transistor 3DA87C to make use of long-range FM transmitter circuit, the circuit is an ordinary three-point oscillator circuit, the article shows that the long-distance transmission circuit with large current emissions, in open areas up to 1KM, I will purchase components, hands-on testing according to the schematic assembly, components, according to the requirements of the article, use transistors with a blue dot to mark greater than 80-fold magnification, but the frequency of the experiment found that it is not falling 88 - 108MHz within the normal FM band, but whatever adjustments capacitance and inductance, were lower than 88MHZ is approximately seven dozen MHZ frequency point, the author is TESUN radio with TV audio reception of the radio to normal reception, and later access to information that is the fT of the transistor cutoff frequency parameter value is not enough, not to mention its oscillation frequency to go up.

       In order to improve and they can launch it from the normal FM radio frequency falls within the scope of the receiver, had to find other high-frequency transistor, introduced the use of many electronic newspapers often D40, C1971, C1972 as a high-frequency oscillation or power amplifier circuit, to increase its output power from launch, but such high-frequency transistor market is difficult to buy, and even buy, most of these fakes, can not be used. Was found with the C3355, this transistor cutoff frequency of several thousand MHZ, the power of 600MW, sufficient for the FM band, and then make some improvements to the circuit, you can easily create a long-range FM transmitter.


Component Selection: capacitors C2, C3, C4 are high-frequency ceramic capacitor, Ct is 5/25P high-frequency semi-adjustable capacitor, you can also use the digital multimeter after commissioning tests for the same value of the high-frequency ceramic capacitance, L is the diameter of the tube 8mm 0.9 enameled wire wound on a 6-turn from the womb, and then opened about 2CM, center tap, TV antenna or the transmitting antenna used with the same length of wire instead.

Actual debugging to the best of its most long-distance transmission power of not less than 500 meters.

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