My Corsair II doesn't act quite that way.
With the RF gain at zero, wide band audio noise is barely detectable
with the audio gain full up.
With the audio at anything useful, the RF noise rises at about 4 or 5.
Sounds to me as if you have a problem with a stage (probably an IF
stage) making more noise than it should due to a faulty component. Maybe
your RF gain control isn't reducing the gain nearly as much as mine.
When you switch in the "attenuator" remember that's actually removing
the RF stage and that the RF stage gain is chosen to barely overcome the
mixer noise to give the receiver optimum dynamic range. My Corsair II
beats anything else I've used for handling strong signals well and for
copying weak signals too.
In radio receivers there's another 60 or 80 dB more gain than in an
audio system, so 90 dB signal to noise is unrealistic. The gain of a
radio receiver and sensitivity is limited by the random noise of the
resistors that can only be reduced by drastically reducing their
temperature. So that the signal to noise ratio of weak signals (and HF
noise is a great deal more than circuit limited noise) is truly poor.
Well trained ears can copy CW as much as 20 or more DB below the noise,
just takes concentration and practice. That's harder to do for SSB, but
its often practical, with practice, to copy SSB signals at the noise
level.
73, Jerry, K0CQ
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