Icom F121 /221 Squelch time delay issue - wrong capacitor
#122454 (In Topic #107680)
I've traced it down to c327 - it's a 10uF capacitor that sets a voltage reference for a comparator. When the radio isn't keyed, it sits at some DC bias level determined elsewhere in the radio. When another radio keys and the ctcss comes through this circuit, the dc level shifts and this capacitor has to float back down to start amplifying the top half of the ctcss waveform. It seems to me that it's way too big, and the time constant is too long. The schematic shows a 100k resistor as the only path for that capacitor to discharge, so, naturally that's a good 10 second time constant. I swapped it out for a 1uf on one radio and it works much better.
Just wanted to throw that out there and see if anyone has run into this issue.
R.G TWO-WAY RADIO Electronic & consultant
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