On Sep 23, 2005, at 11:07 AM, Peter Chadwick wrote:
> Rich said:
>
> ?
>
> >So, do not use a meter that has sticky bearings.
>
> ?
>
> You still have to set it to around 1.5% of full scale.
I do not set the meter. With the RF gain at 10, the splatter moves the
meter to some level, perhaps c, half-scale. I note the average
reading, move to the fundamental frequency, and add whatever attn is
needed to achieve the same reading as before. The # of db on the attn
is the total IMD level.
>
>
> >The IMD level produced by the transmission of human speech can not be
> found by a 2-tone IMD test.
>
> Agreed.
>
> I use a steady "ahhhhhhhhh".
>
> A 2 tone test is a convenient start, A 3 tone test with 2 of the tones
> very close - say 20 to 30Hz apart - is useful. That really shows up
> the power supply filter capabiliites. For real reproducability between
> measurements, modulating the tx with noise works pretty well. That was
> how they used to measure the IMD of the old analogue multi channel
> telephone systems.
>
> 73
>
> ?
>
> Peter W6/G3RZP
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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