Posted by
Edward R Cole on
Jul 24, 2011; 1:54am
URL: http://elecraft.85.s1.nabble.com/RF-gain-sweet-spot-tp6614675.html
I'm guessing this "effect" is an artifact of the AGC parameters and
the level of ambient noise. I would love to see a chart of AGC
level, K3 gain, and RFG bias voltage.
I see a flat zone between RFG at maximum and at 3-o'clock position
when I either have no preamps activated and when I activate the PRE
(internal preamp). Gain appears flat over that range and I hear no
change in audio level with antenna connected. Remember that I have
extreme hearing loss so it may mean I unable to hear the change even
if there is one.
When I run my ARR preamp, the s-meter indicates S4.5-S5 and the
s-meter immediately rises when I rotate the RFG to a lower
setting. There is no flat region. Since my preamp has 24-dB gain
and K7WIA is using a preamp with 15-dB gain, they are not exactly
compariable. The approx. 9-dB extra gain may be saturating the
follow on Rx circuits.
A precise measurement of SNR (with a weak signal) vs RFG voltage
would be interesting.
Perhaps Eric or Wayne will comment.
73, Ed - KL7UW, WD2XSH/45
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