The circuit was designed to create an automatic repeater that would retransmit a received signal over the amateur radio frequency band.The operation of the circuit initiates by commencing the squelch circuit of radio 1 as it receives a radio signal.
The squelch circuit cuts off or suppresses any of the functioning receivers when the signal becomes weaker than the noise.The presence of audio signal turns ON the MOSFET, even by a small amount of the signal. It will continue to function as amplifier and as switch until the audio signal sets off. During this operation, radio 2 is ready for broadcasting. As radio 2 goes on air, it regenerates the signal received from radio 1 through C1 and P1 content.
This little circuit can turn two hand-held radios into a makeshift repeater. Any radio will work fine as Radio 1, but Radio 2 must be a Yaesu, or some other type that also goes on the air when its microphone input is shunted with 1-2 kiloohms
As soon as a radio signal opens Radio 1’s squelch circuit, a tiny amount of energy stolen from the audio signal turns on the MOSFET and it conducts as long as the audio is present. While it conducts, Radio 2 is on the air, retransmitting the content supplied by Radio 1 through C1 and P1
The BS108 has a conveniently low G-S threshold voltage. The other components’ characteristics are not critical, but it would be wise to stay close to the values shown in the picture, or at least take them as a starting point for testing.
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