Radio WC6W wrote:
>
>
>On Thu, 26 Oct 2000 21:24:20 +0200 Peter Sundberg <sm2cew@telia.com>
>writes:
>>But maybe we should start testing other amps than DAF's without using
>the
>>two tone test. A poorly regulated screen power supply in a grid driven
>amp
>>should maintain a pretty stable voltage with a two tone constant
>modulation
>>not giving away that the amp would sound bad when modulated by speech.
>>True or not .. ?
>
> IMD testing using white noise is possibly a more accurate methodology
>and more representative of a real world voice situation. A good
>description of the technique may be found in "Single Sideband, Systems &
>Circuits" by Sabin & Schoenike, 1987 pp 473-477.
The problem with the white noise test is that, like the two-tone test,
it does not test the effect of variations at the word or syllable rate.
If the only test is at high frequencies, the capacitors in the HV and
bias supplies will maintain constant voltages - but if tested with real
speech, the voltages swing all over the place.
>
> Here in the states, I believe that the FCC still uses the two tone
>standard for their distortion tests so, it makes sense that if that is
>the test you need to pass, that is the test you run.
>
If it is the only test, you learn the truth but not the whole truth.
>
> It may be have been forgotten by now... but, when I got entangled in
>this thread 24 hours ago, I specifically stated that I am NOT an advocate
>for the DAF concept. I just like to see the facts & numbers kept neat!
My position also - neither for nor against, but very much on the side of
open-minded discussion.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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