[Photo] 1.5V mini FM microphone

The microphone is as small as a finger and uses only 12 components. The working frequency is stable, the transmission distance is about 30 meters, and it can reach more than 100 meters when powered by 6V.
The circuit is shown in Figure 1. BG1 and C1, L form a high-frequency oscillation circuit. Because the BG1 inter-electrode capacitance Cbc and C1 are connected in series and then in parallel with C3 and L to form an oscillation circuit (see Figure 2), because Cbc changes with the audio signal strength, the oscillation frequency also follows Changes have taken place, and the frequency modulation of the city of Lhasa has been realized. The C6 in the circuit is relatively large, and a good emission effect can be obtained in non-professional occasions. The launch distance is related to the working current of the launch tube, not determined by the Pcm value of the tube. The upper bias resistor R2 can change the output current of BG1.
When choosing BG1, the fT of the tube must be ≥30mA, such as N4401, 3DG130G, 2G711D, etc. The inductance L is divided into two coils to avoid the trouble of tapping, but the winding direction must be the same, otherwise the polarity of the electromagnetic field will be opposite and cancel each other. Can't vibrate. L1 uses Φ0.5㎜ enameled wire to wrap 4 turns on Φ5㎜ skeleton, L2 wraps 3 turns. The antenna can use a 0.6 meter long flexible wire. During production, the C4 span arch should be placed on the welding surface and lie down on the BG1 degree.

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