Squelch of radio receivers is always controlled by RF level rather than audio.
1) I'd implemented the circuit but couldn't get the required output.
MPF103 and audio amplifier section not implemented as in my circuit i'm using LM4871 for amplification.
I'd just monitored the voltage at 560K resistor and collector pin at Q1 but output remain same in both cases when signal is present and without signal (HISHHH audio ouput).
2) Also I implemented the active high pass filter (with different cutoff frequency - 3KHz, 3.5 KHz) but could not achieve the required output.
View attachment 142610
Assumption: Squelch noise (HISHHHH sound) is above 3KHz frequency so I've set the cutoff frequency 3.5 KHz and amplify the noise so that it can be monitored.
How the other walkie talkie maker companies like Motorola, Kenwood,..etc are control the squelch??
Hi,
Single supply without DC input biasing.
Klaus
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