> The R4C AGC was discussed and even modified in a CQ magazine article back
in the
> 80's by W3RJ. It took the flatness out of the AGC clamping area so that
signals
> that were between S7 and 30 dB over S9 would vary in volume by about 3 dB
> instead of the stock 0 dB. The thought was to allow some loudness
separation by
> your ear.
I initially took the opposite approach. I constructed a totally separate AGC
board with variable but very high gain in my R4C's. What I found was the
more gain I used in the AGC loop (which makes the output level flatter with
signal level change), the less I liked the AGC. I found I needed a slope
near the noise floor, so weak stations and noise did not turn to single
level of "mush".
I could never understand why K3LR said he liked the crummy flaw-filled AGC
system of the R4C....until I made it better. The more it held volume equal
at low signals levels, the worse the receiver was with weak signals in rough
noise or in pileups.
I personally find a slope up around S9 doesn't mean much one way or another,
because signals are so good anyone could copy them 100%.
On the other hand allowing gradual deterioration of AGC leveling at -120
to -130dBm (my normal winter noise level) to -100dBm is critical for copy of
weak signals. This is especially true if there is a pileup of weak signals.
Listening towards Europe or Japan on a quiet winter day a signal
round -125 to -130dBm signal would be about the minimum discernable signal
at 250Hz bandwidth. When I change SW or SE the noise is commonly 5dB or more
higher because of tropical noise. The noise also varies over short term, and
might contain static crashes or other rough noises. I strongly prefer to NOT
have flat AGC at the low end, but I don't like anything that knees over into
an abyss on lower bands. 20 meters and up, where everything is always a
smooth steady hissing, is another story.
> That being said, how hard would it be to find the Orion AGC parameters
that
> would cause the exact same AGC characteristics as the R4C?
I'm not aware of any way to do that. As far as I know it has a hard
threshold, which is probably excellent for smooth steady noise. Maybe Bill
or someone else knows how.
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