[TenTec] Receiver ratings question, IP3 and synthesizer noise

[Gary J FollettDukes HiFi]

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