All the early TenTecs had audio derived agc from the Triton to the Corsair
II. It began as a cheap way of obtaining selectivity without the use of of
expensive crystal filters. A narrow audio filter is ahead of the take-off
point for the agc voltage which restricts what signals the agc can respond
to. The result is very narrow passbands of 150hz with near IF filter like
performance. After the Triton series, in the Omni, they decided to add the
xtal filter in the IF amplifier in addition to the sharp audio filter
resulting in awesome selectivity by 1980 standards. Also, a very effective
notch filter was added to the audio filter. Like you mentioned, the trade
off was the pop you hear on strong signals. After the Corsair II, agc was
derived from the IF. Audio filters continued to show up in the newer rigs
but became an aid instead of a necessity.
The IF amplifiers in the older rigs ran at a constant, optimum gain and the
agc voltage was used to bias a diode which shunted the RF to ground
accordingly.
One thing to consider is that the old AF/agc system is much like todays
DSP/agc system. The performance difference being agc attack speed and a much
wider range of filter options available with DSP.
Steve
N4LQ
----- Original Message -----
From: <ARDUJENSKI@aol.com>
To: <tentec@contesting.com>
Sent: Thursday, November 07, 2002 4:25 PM
Subject: [TenTec] Audio vs IF derived AGC?
> I come across discussions of AUDIO DERIVED vs IF DERIVED AGC. Is there
that
> big a difference in perfornance? Is the Corsair II the first of the Ten
Tec
> with this feature? Does it perform that much better than the Corsair and
> earlier models?
>
> Or is all this RF vs AUDIO derived issues not really a measure of
performance
> but just that annoying (to some) pop sound)?
>
> Alan KB7MBI in Woodinville, WA
> FISTS 5702 Proud member of ARRL
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