This is a FM Wireless Microphone circuit. Which we add one transistor in the RF amplifier. So this circuit has two resonance circuits and also two trimmers. This cause has the Higher efficiency and transmission far up.
The working of FM wireless microphone
Figure 1 Two transistors FM wireless microphone circuit
The microphone acts as the audio receiver to convert voice to an audio signal. It will come to C2-coupling capacitor into the base of TR1-transistor.
Which this transistor and a few parts around itself, have 2 functions.
First, they generate the high-frequency oscillator.
Second, they mix the audio signal into radio frequency (RF).
Then, the RF comes to the base of TR2 through the coupling capacitor-C5. The TR2 amplifies the RF comes out of collector, send out of the antenna.
At collector of TR1 and TR2 will have a copper wire, easy to builds. They are working like a general coil.
As Figure 2, the components layout and wiring of this project. I am so sorry for cannot show PCB layout for you.
Testing the FM wireless microphone
First, apply the 9 volts battery to the positive terminal (+9V) and negative (G terminal).
Second, for ANT point connects to the coil.
You need to scrap the liquid coatings out of the copper coil before soldering it.
Then, Set the FM radio stations to positions 88 MHz.
Next, use a plastic screwdriver to gently adjust the trimmer VC1, Until it whistles howling out the radio.
After that, Try to speak into the microphone.
However, if no sound on speakers. You may try to turn the radio to about 100MHz. If this is still no sound, you turn the radio all the way to 108MHz and try again.
Then, adjust Trimmer-VC2 in order to get more distance.
Also FM wireless transmitter
FM wireless transmitter circuit Electric guitar FM transmitter circuit from Acoustic FM transmitter circuit, 2 watts (2 kM)
The components list.
TR1, TR2—2SC458, 2SC828, 2SC945, 2SC1815
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