[Amps] Checking for IMD

[Tom W8JI]

> That places the majority of those products outside the 
> passband of your
> sideband filter on BOTH sidebands.

It looks to me like one group of IM3 products will be mostly 
OK, except carrier offset causes a gap.

That group will miss close-spaced mixing of IM3 products 
however, so it is incomplete. One group of  IM3 products 
will be totally missed and that group would be the group 
that contains the close-spaced mixing of closer spaced 
high-frequency tone IM products.

Say you has a 2000 and 3000 Hz tone mixing. The closest IM 
products would be 1000 Hz above the highest tone and 1000Hz 
below the lowest tone. Neither would be detected with a 
sideband switch.

As for testing on the air I see one huge problem. The noise 
window is wide and there probably is a lot of junk from 
other things in the passband. This is a test that can easily 
convince people they have no problem when they do for 
multiple reasons, and it can also do the opposite if the 
receiver is operated in a way that makes it limit 
performance. This is especially a problem if someone with a 
wideband ESSB signal would use that method.

http://www.w8ji.com/mixing_wide_and_narrow_modes.htm

73 Tom