Tuesday, June 23, 2009

The airband receiver squelch revisited

....Impossibly to find a stand alone (and simple) squelch in the internet and in books that I have.

Had to cut and past from a bigger online receiver design and rework some changes.
Since last time I studied op-amps somewhere last century I forgot that ideal op-amps are not real ones, that's why there are so many models. The original design (first rework) was not working due the specific nature of "real" op-amps... the 741 didn't worked as expected.

It's a simple comparator circuit without hysteresis.... that is done by the lack of precision of the adjustable potentiometer movement (backslash et all), if it was a multiturn, probably hysteresis was a good thing to have.

The schematic:




















There is space for improvement, for instance if the signal is to strong it will not block the audio (max signal value no enough), changing the 1k ohm resistor for a bigger value will allow that, in the other hand it is nice if your friend is calling you on frequency near your house....

And the video of it working (not a very explicit example since exactly when I was testing all the channels were with signals opening the squelch level I set):


video

1 comment:

123 said...

It was certainly interesting for me to read that post. Thanx for it. I like such topics and everything that is connected to this matter. I definitely want to read more on that blog soon.
Alex
Cell blocker