> We are looking for an easy method here. Swapping side
> bands does just that.
It's certainly easy.
> 4.5 KHz doesn't get you out far enough to get all products
> for all voice
> frequencies either, but again we are looking for an easy
> way to get a
> ballpark idea.
Let's see.
The frequency spread of IM is the difference of the two
frequencies. So if we have speech (an ahhh won't work well
to replicate real speech) we can consider the frequency
spread of the lowest and highest frequencies.
You'd get all of the third order opposite sideband products
but only some of the 5th and higher.
> Look at what swapping side bands does: It is a fixed
> repeatable move in
> frequency from the main signal and the attenuation between
> those two
> frequencies is a minimum of 40 db. Anything that is heard
> on the opposite
> side band is going to be pretty much distortion products.
The question os from what. The receiver or transmitter? The
test would be with the main signal INSIDE the roofing filter
of most radios. RECEIVER IM3 dynamic range is between the
40dB area to 90's on most receivers, but the useful AGC
measurement range using the S meter would be less because
you couldn't go to noise floor with the S meter.
With a better close-spaced receiver you'd be OK, assuming
you used it properly. Not with some radios though!
It would be a lot better to get the roofing filter into
action. A sideband change doesn't do that on most radios.
> So anything you hear on the other side that is less than
> 40 db below the
> wanted side band level is going to be distortion products.
You just have to know if they are from the receiver or the
transmitter.
73 Tom
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