Then what if we *deliberately* inject hundreds, if not thousands of discrete RF
carriers into our SDR receivers from say...an internal RF carrier or noise
generator, mixed with the desired RF signal to mitigate OL caused by a few
strong carriers? It would be interesting to see the math and note what, if any
reasonable limits apply, even if the amount of OL protection is small but there
nonetheless. If this is a viable form of OL mitigation, then by now, someone
must have already addressed this, possibly in an academic or IEEE paper?
Paul, W9AC
That roughly describes the FM broadcast band near San Bruno
Mountain, south of San Francisco, which is chock full of
FM transmitter sites. It is an extremely difficult RF
environment. The picket fence spectrum definitely is
not beneficial. Instead, the stations mix with each other
in the receiver front end and fill in any clear channels
with garbage. I did some consulting for a company that
made FM-SCA receivers and developed an 8 stage voltage tuned
preselector for their receiver that worked as well as
the six stage air variable preselector in my circa 1978
Technic's tuner that sold for $450 at that time. I also
tried a WJ mixer with 1/2 watt LO drive as the front end
of a superhet, but without a preselector. There was
no comparison; the non preselected high power mixer
was nowhere near as good as the preselected receivers.
Of course, an ordinary car radio driven near the
mountain is far worse than than any of the above.
At the Maker Faire a couple of years ago, they had
a start up company that was exhibiting an FM receiver
that digitized the entire FM band. I'd like to see
what that would have done around San Bruno Mountain.
Rick N6RK
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