On Jul 27, 2004, at 1:17 AM, peter.chadwick@Zarlink.Com wrote:
Some professional tests use a very narrow spacing between tones - as
low as
30Hz - to simulate the syllabic nature of voice, and to exercise the
power
supply regulation. Another approach, which, if I remember correctly,
has
been advocated here by Tom, W8JI, is to use a three tone test with two
of
the tones very closely spaced. As Steve, G8GSQ says, the screen current
varies at a frequency dependent upon the tone spacing.
Because of the peak to average nature of a voice signal, it isn't easy
to
relate the performance on a two tone test with that under voice
conditions.
The advantage of a two tone test is that it does (or should!) give a
number
that can be reproduced in testing by other people.
Peter -- Should, yes. With 30Hz or so tone spacing, it's going to
take an incredibly capable spectrum analyzer to separate and measure
the 3rd and 5th order products. If the thing we are concerned about is
on-the-air rotten splatter from voice modulation, why not measure
splatter from voice modulation by listening to the adjacent channels
with another receiver? Sure, a precise ± 0.1db measurement is not
going to happen, but, ± a couple of db accuracy is good enough in this
case. // cheers
...
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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