Gary writes:
> It is no poorer than tuning the receiver to another frequency
> to listen for IM products. The same kind of noise and interference
> will exist on other frequencies too.
Gary, there is one problem with your analysis. Most modern rigs
have an 8 to 15 KHz wide filter in the front end (first IF).
This filter is symmetric around the "carrier."
When switching to the opposite sideband the fundamental tones
are still inside that filter. However if one stays in USB
and tunes down by 3 to 5 KHz, the fundamental frequencies
are down on the slope (or outside) the front-end (roofing)
filter and much less likely to generate additional IMD in the
receiver. By putting the fundamental tones outside the front
end filter, the receiver is also more sensitive to the IMD
and can potentially be used without AGC allowing more accurate
measurement.
73,
... Joe, W4TV
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