[Amps] 4CX1500B

R.Measures r at somis.org
Fri Sep 23 18:07:06 EDT 2005


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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