Mechanically served with special triode ----- fm Transmitter

Mechanically served with special triode, FM Transmitter Keywords: Mechanic FM transmit circuitry Be Mechanical frequency modulation circuit The above figure shows a long-distance FM transmit circuit that is made from a general triode 3DA87C. The circuit is also a common three-point oscillating circuit. In the article, the long-distance transmit circuit is launched, and the large current is transmitted. 1km, the author purchases the component to assemble the element, according to the principle map, the components need to be more than 80 times the magnification with the blue point logo, but found that its frequency is not falling at 88-108MHz in the experiment Within the normal FM band, no matter how to adjust the capacitance and inductance, it is about 88MHz to be about 70 MHz frequency points. The author is a TV soundtrack to receive the radio to receive function, and later review The data found that the FT cutoff frequency parameter value of the triode is not enough, so that its oscillation frequency is not fed. In order to increase the emission distance, it can be found within the reception range of the normal FM radio, and many electronic newspapers are often introduced to D40, C1971, C1972 as high frequency oscillation or power amplification circuits. With its large power output, it is difficult to buy, but this high-frequency triode is difficult to buy, and even if you bought it, most of them are some fakes and cannot be used. Later, I found C3355, the cutoff frequency of this triode was a few thousand MHz, and its power was 600MW, which was used for the FM band. Then make some improvements, which can make it easy to make a long-range frequency modulation circuit. Element selection: Capacitor C2, C3, C4 are high frequency porcelain interversion, CT is 5 / 25p high-frequency semi-adjustable capacitor, or after debugging, use digital multimeter to test high frequency porcelain Capacitor, L is a tube of the 8 mm of a lacquer line of 0.9, and then pulls about 6, then pulls open about 2 cm, intermediate tap, and the transmitting antenna is replaced with a television antenna or wire with the length. Reactive debugging to the best The maximum distance of the transmit power is not less than 500 meters.

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