Richard wrote:
> >Rich,
> >
> >How did you come up with 4.5 kc offset?
>
> This is the separation needed to stop the Tx filter skirt from
> overlapping the Rx filter skirt. Thus, one hears only genuine, bona
> fide, feculence without any fundamental. For a double filter radio, the
> steeper skirts allow an offset of c. 3.6kHz - which yields a better
> measurement.
>
> >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.
>
> True, however, including the fundamental in the measurement - due to
> filter passband overlap - is seemingly a greater source of error.
>
> >Wouldn't multiple tone IMD testing give a more accurate picture?
> >
> Not in my experiences. A human voice gives the dynamics a workout.
>
> >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.
> >
> Agreed, but a double-filter receiver would be needed - and you would be
> measuring unwanted sideband energy instead of intermod products.
>
> cheers, Gary
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
Good points Rich, listening will certainly catch things like alc problems that
a
2 tone test will not. I am an advocate of using the receiver as a piece of test
equipment. Probably the best in most shacks for many purposes.
73
Gary K4FMX
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