> > IM products are not symmetrically dispersed Gary. Where they are USB or
LSB
> > depends on relative level (and I would guess phase, I need to think
about
> > that) of the original frequencies.
> >
> > 73 Tom
> >
> >
> >
>
> Hi Tom,
>
> If IM products are generated at RF (after filters) I don't think that
> there is a difference. Each signal should modulate the other equally.
There sure is a difference! I have to be very careful doing two-tone
receiver tests to make sure the levels are equal, otherwise one 3rd order
product will be much stronger than the other.
The stronger signal generally becomes the local oscillator and is more
limited (gain compression), while the other is a linear product of the
mixing. So 2f1-f2 is not the same level as 2f2-f1 when either F2 or F1 is
stronger.
The (input power to output power) transfer functions of an amplifier or any
less than perfectly linear stage are complex, and always vary with level.
I'm sure there are other reasons also.
73 Tom
|