I think I have that mod in my old files somewhere ... I believe it is a
change to the time constant / attack time of the audio AGC (by changing
a cap and resistor as I recall). I did this and did NOT like it, it
nearly ruins the QSK when you get things about right vis a vis "thump"
so I went back to living with the occasional thump and enjoyed the nice
QSK and audio filters within the AGC loop. Ten Tec made fair tradeoffs
there, I couldn't improve on it.
Clark
On Aug 16, 2006, at 8:19 AM, Dr. Gerald N. Johnson wrote:
On Wed, 2006-08-16 at 06:58 -0700, John R wrote:
I'm a little late coming to this subject, but QST ran a fix in its
"Hints and Kinks" for the AGC "pop" problem back in 1982 or l983.
Someone may have more info on this.
The fundamental cause of thump in analogue Tentec radios is that the
AGC
is derived from audio sometimes after some audio filtration. In any
case
the audio wave rises more slowly than the IF wave and that delays the
attack of the AGC, in the mean time there is time delay for signals
passing through the crystal filters and post detection filters that is
already past the gain controlled stages when the AGC finally acts.
Hence
the thump or click. The filter time delay is the most of the problem,
most cures work at speeding the AGC attack with changed time constants.
WA3JPG
Clark Savage Turner, J.D., Ph.D.
Professor of Computer Science
Cal Poly State University
San Luis Obispo, CA. 93407
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