For the most effective and efficient use of the battery capacity, to prolong the operating time of the transmitter wireless microphones without replacing batteries, we recommend using an active switch on the acoustic signal of bookmarks, which consumes little current in standby mode.
The converted audio signal from the microphone PM arrives on two-stage audio frequency amplifier VT1, VT2, the gain of which is set by resistor R3, and then fed to the input of the generator VT3. The RF generator is the scheme of the inductive treatacne. Contour L1C8 tuned to the frequency of 140 MHz.
Consistent feedback is performed by the capacitor 7. Mode DC voltage set by a resistor R6.
Chain VD1,VD2,C5 detects the audio signal and used to control the power VT3. With the help of resistors R3, R6, choose such a bias voltage to the transistor VT3 in the absence of a sound signal was in the cutoff.
Transistors VT1, VT2 must have a gain of at least 150, diodes VD1, VD2 - ger-monavie, type D9. Coil L1 consists of 4+1 round wire with a diameter of 0.68 mm, wound on a mandrel with a diameter of 4mm. the Coil L2 is wound on top of the L1 wire 0.25 mm and contains 3 coils.