In article , "Tom Holden"
writes:

In researching desirable AGC characteristics that might be applied to the RS
DX-394 over a year ago, I came across the terms 'delayed' and 'hang'.
Thought they were interchangeable but on reading the ARRL 2004 Handbook, it
seems that 'delayed' means that the attack speed on the RF stages is slower
than on the IF stages or is relatively delayed. According to the HB, "This
prevents a premature increase in the receiver noise figure". On the DX-394,
I found and removed an electrolytic capacitor in the AGC line of the RF
stages that has the effect of slowing the attack relative to that of the IF.
Can't say I hear any difference with it out. I would have thought that we
would want the AGC attack to be fast on all stages in order to avoid
momentary overload.

According to terms used a half century ago in tube-type receivers,
"delayed AVC" (they used 'AVC' back then instead of 'AGC') just
meant that AGC action is delayed from taking effect until the signal
level rises above wide-open gain. Wasn't a time delay, but closer
to "hold off" voltage of some sort on the AGC control voltage action.

"Attack" and "decay" meant the time of response of the AGC, in
the same manner as audio-only control circuitry for broadcast
audio modulation input. "Attack" being the onset of a signal and
subsequent audio gain reduction time..."decay" being the release
time of any audio gain reduction control signal, that 'decaying' back
to original high-gain amplification.

I suspect that the original "delayed AVC" came about from two
reasons: First was that 'communications receivers' of olden times
usually tuned a rather wide band, usually 1:3 in frequency range
and the non-AGC gain varied by almost the same amount as a
result of tuned circuit impedance changes (tubes would amplify
almost entirely by only voltage changes when running Class A).
A hold-off on the AGC action handled the difference in overall gain
at the extremes of tuning.

Second, and I suspect the stronger reason, was that customers
could hear the front end noise in the speakers (with AGC held
totally off and gain wide open) and get the impression of a "really
hot receiver!" :-)

It's easy to get any kind of "delayed AGC" or hold-off on AGC
control with a DC bias on the detector.

As to the attack and decay times you specified, seems good to
me. That can be set to suit the individual listener.

Len Anderson
retired (from regular hours) electronic engineer person