archive: SETI Disabling R-7000 AGC

SETI Disabling R-7000 AGC

Randy Stegemeyer ( )
Sat, 26 Dec 1998 17:15:38 -0700

I disabled the AGC on my R-7000 by cutting the top lead of R-115 on
the IF board. This resistor is in the base lead to transistor Q18,
which is the AGC amplifier. With this resistor opened, no voltage from
the AGC rectifier diode D28 can reach Q18 so it never attempts to lower
the gain of the receiver.
After you take the top cover off, and facing the front of the
receiver, R-115 is located about 5 inches from the left side of the
receiver, and about 4 inches from the front. Its plainly marked and is
standing on end. The lead coming out of the top is easy to clip and
easy to solder back if you need to. I never use my R-7000 in AM mode
for anything other than radio astronomy so I did not add a switch for
turning it on and off, but it would be a simple matter to do so.
My modification seems to be working fine for me but I would be
interested in hearing from anyone with problems or a better idea.

Randy Stegemeyer