Manufacturers have gone mad about IMD in receivers but can you use it? e.g. a
+40dBm TOIP with a 10dB NF. In SSB, that's an rx noise floor of -130dBm and an
SFDR of 113dB. To use that, you need phase noise of -147dBc/Hz averaged over
the 3 kHz bandwidth at whatever offset you are worrying about.....even that
leads to a 3dB degradation. So to properly use that TOIP, the phase noise
should be 10dB lower or -157dBc/Hz.
To quote Dominie Sampson "Prodigious!"
Measurements suggest that 95 to 100dB of instantaneous receiver dynamic range
i.e. phase noise or imd limited, is about all the average amateur needs....
Now how far do you need to improve transmitter wideband noise to make a
difference to other users? Just consider the wide band noise effects of a 250kW
broadcast tx on say 7310 and how much trouble that will make.......
Although the degradation from about -30 or -35dB IM3 wrt tone has been
undesirable, I do wonder how much difference it really makes compared with the
effects of 'all knobs clockwise' which we will never stop.
For commercial ISB, the usual requirement has been -36dB wrt PEP, and that's
based on acceptable crud in the wanted sideband. It's unfortunate that bipolar
transistors on 12volts are inherently limited, but that's what the market
appears to want at the moment.
73
Peter G3RZP
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