[Amps] Re: IMD

[Richard]

>
>
>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.
>
Amen, Gary.  Rocket science, it's not.  

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
end