Audio AGC pop

[Steve Ellington]

Tom Cooper wrote:
> 
> The audio derived AGC in the older T-T radios has always bugged me,
> but I have never had much success in getting rid of the "pop".
> 
> Replacing the 4.7 mfd AGC electrolytic cap with a tantalum cap does
> improve things.  W3TS built a little MC1350 based, RF derived AGC
> voltage generator for his Corsair II, but the one I built works like
> many of my RF projects (either not at all or self oscillation).
> 
> I am experimenting with an Analog Devices SSM2165 compressor/limiter
> just before the AF gain pot and it helps, but there is still a "peck"
> on strong CW signals.  I guess I should just live with it since my
> ears are better protected, but it's irritating, like having a small
> stone in my sock.
> 

I had the brilliant idea of putting my dsp unit in line with the audio
preamp, ahead of the agc. I worked great but added even more delay to
the agc and really made a big pop. 

There are three possible cures. 

1. Put an agc detector/amplifer ahead of the audio stage like other 
   radios have.

2. Put some kind of audio limiter after the agc point in the af stage.
   Old Hi-Fi amplifiers had what they called a "pop filter". Perhaps a 	
   diode could be put in the right place to shunt the loud pops.

3. Buy a Paragon, Omni 5 or Omni 6.


I had the big idea of putting the dsp ahead of the agc in my Triton. Due
to the extra delay, it made the pop even worse. I think if you try using
one of the newer DSP units such as the MFJ which has the adjustable
noise limiter feature you may see a big improvement.

N4LQ Steve

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