Rich,
How did you come up with 4.5 kc offset? I am assuming that you are using the
receive filter on the same side band with that offset? With that setup I would
think that you would only see the products of the higher audio frequencies and
not the lower ones as they may not fall that far away. Wouldn't multiple tone
IMD testing give a more accurate picture?
Although I do agree that it gives a good snapshot of excess bandwidth. I do
kind of the same thing but I just switch side bands on the receiver and note
the difference. However a guy with lots of lows has more energy on the other
side band. But it still is a good quick check of bandwidth.
73
Gary K4FMX
Richard wrote:
> >Hi Rich,
> >As you know there's a lot of postings on "Amps" about IMD. Please tell us
> >how to measure ( that's you ) IMD.
>
> >Bob, w5pvr@gower.net
>
> ? The IMD produced by a human voice can not be approximated accurately
> with a 2-tone test, so it must be measured with a human voice. Here's
> how I measure it. With VFO-A and c. 40 db attenuation, note the S-meter
> reading on the fundamental. Offset VFO-B 4.5kHz up for measuring LSB IMD
> or 4.5kHz down for measuring USB IMD. Remove attenuation until the
> S-meter is the same as on the fundamental. The change in db attenuation
> is the total IMD of the signal. An alternative method is to make a graph
> of S-meter indications vs, db using a step attenuator, switch between
> VFOs A & B, note the S-meter indications, and subtract.
>
> have fun
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
>
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