Having reread the definitions from Sherwood’s page on receiver test ratings, I
have to ask, what is the significance of IP3 in a receiver that has no mixers
(any direct digital SDR)?
I also have to ask, what is the significance of synthesizer noise in a
receiver that has no synthesizer (any direct digital SDR)?
These two existing ratings indicate that almost every DSP receiver is better
than any heterodyning receiver, even though it is common knowledge that
IC-7300’s are being dumped on the used market because they perform so poorly in
tough RF environments and even Icom recommends use of a preselector to correct
the problem.
Also, now that I pay closer attention to the full description of the Flex and
other SDR’s, I see the “B” rating for the front end selectivity. This tells me
that the various DSP radios must use band limiting input filters to help the
DSP in overcoming the problems that would occur if a strong broadcast signal
were being received at the same time as a 2 microvolt CW signal. Apparently
some (Flex) do a better job of this than others (Icom).Either that or the front
end selectivity ratings for these radios is boiler plate stuff with no real
significance.
Perhaps it is time for a new select criterion for future DSP designs?
Gary
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