AI4QJ wrote:
. . .
When other people complianed of noise, it was a common practice for them to
use 2 transceivers or a transmitter with a separate receiver on 75 80m. The
transmitter of course was tuned as close to 1:1 as possible but the receiver
was tuned to a higher VSWR to 'tune-out' the noise, yet the signals higher
than noise came through very well. I was actually quite surprized to find
out how much noise there was on 75-80m when I was actually able to
transmit/receiver at a VSWR close to 1:1.

This was/is something other people do routinely and is somewhat better than
an old wivws tale. Of course, by not tuning in the noise, you risk not
tuning in the very weak stations but you can come to an accomodation where
you hear mostly what you want to hear while getting rid of noise. The
attenuate button does not work as well for this (my opinion).

If so, what do you suppose the mechanism is by which the shorter antenna
distinguishes between signal and noise?

If the antenna has a high VSWR, although you cannot transmit efficiently,
signals significantly stronger than noise level can still be received, or so
I think as do others. I am not sure at this time 'why' the gain of the noise
is not comparable to that of stronger signals when adjusting the receicver
for normal listening volumes. But when listing at 80m, you can simply take a
20 foot piece of wire and hang it indoors and you will hear a lot of
stations quite clearly and the noise level will be much lower than when you
tune it resonant.
. . .

Certainly the noise level will be lower than when you match the antenna.
but so will the signals. In exactly the same ratio. And if you can hear
the signals clearly with the short antenna, you can hear them just as
clearly with the longer one -- unless you're overdriving something to
the point of nonlinearity with the longer antenna.

If you think you're actually improving the signal/noise ratio by
mismatching the antenna, then you've claiming that mismatching has
somehow given it the ability to tell the difference between what you
regard as "signal" and what you regard as "noise" even though both are
presumably on the same frequency. Or perhaps if the signal and noise are
coming from a different direction, the mismatch is causing a change in
the antenna's directional pattern. Neither of these fits with any known
theory, so I'd have to see some really solid quantitative measurements
to be convinced this is more than an old wives' tale. (And even then,
I'd be looking very hard for an explanation that fits the theory which
has suited us so well for over a century.)

Mismatching the antenna should do no more nor less than turning down the
RF gain control. Have you tried doing that instead?

Roy Lewallen, W7EL