John,
Yes the RF gain control changes the AGC threshold level - just like setting
it in the AGC menu. One of the original Orion firmware developers, Doug
Smith, wrote in a paper describing the Orion Digital AGC System:
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"In digital AGC systems, it is relatively easy to provide a variable
threshold or "knee." Input signals below the threshold do not actuate the
digital AGC and are not compressed. At thresholds well above the receiver
noise floor, a receiver therefore gets quiet when only puny input signals
are present in the passband. At thresholds near the noise floor, all signals
are boosted to meet the output-level criterion. The net effect of a variable
threshold is very much like that of an IF gain control."
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Consequently, if you "ride the RF gain" and set it for a good audio level on
a stronger signal, weaker signals will not activate the AGC and they will be
too low in volume. I've never been fond of this process. I think it was a
"crutch" to offset the gain distribution issues in the new Orion V2
firmware. There was an AVC loop in the V1 code that prevented the audio
stages from being overdriven and distorting. That code was taken out of the
V2 firmware and there have been peak signal distortion issues since. That
started some people doing what you described with the audio and RF gain
controls. Unfortunately you are seeing some of the unintended consequences
of operating the radio like that. Hopefully Ten-Tec will address the
distributed gain level issues in the next Orion V2 firmware release - maybe
they will put the ALC code back.
73, Merle - W0EWM
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