>It would be hard to not have such AGC response and still have the AGC
>work well on audio signals. Probably what it needs is a dedicated DSP
>for the AGC that could discriminate between a pop and a fast rising
>voice syllable or CW dit and could limit the amplitude of the pop
>without reading it on the s-meter but do the AGC for the preferred
>signals properly. Probably even with a DSP handling the AGC, it would
>also need to handle the audio so it could delay the audio while it
>determined the appropriate treatment.
This is profound truth. Rice filters can take a mushy, hard cw signal and
turn it into a bell like tone. They take gentle babble of background static
and turn it into a constant, head-throbbing roar. Yes, those rice filters
act almost like the filter in a power supply, smoothing out the ripple and
giving us a steady state drone.
As for the pop. Yes, the older TT rigs with the audio derived agc reacts to
sudden pulses with a loud WHACK sometimes. The filter response is just too
fast for the agc to squelch it. One observations come to mine here. The
Century 22 had audio derived agc but no WHACK. The possible reason my be
how the agc voltage is applied. In that radio, it is simply applied to the
base of a transistor which acts to shunt the audio to ground as it leaves
the detector instead of decreasing the gain of the I.F. amplifier as in
other TT rigs.
I believe I will experiment with this simple circuit by adding it to the
existing agc line. Perhaps a threshold can be set so that only very strong
signals cause this extra agc action. All that's needed is one transistor and
one resistor!
Steve N4LQ
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