On Jul 25, 2004, at 9:49 AM, Will Matney wrote:
Exactly, and is my point here. Yes, two tones do produce some variance
but that is what the test was around. What happens when you add voice
with all the frequencies and harmonics like I'm speaking of? Does the
IMD raise or stay the same? With the two tones, you'll have those two
frequencies, their products from each because of mixing and some
harmonics from each of them. Each multiple with a lower voltage than
the center frequency which I assume your speaking of varying the
current and voltage. Keep in mind though that still each are at a
constant peak to peak voltage (each frequency with harmonics and
products lower) because of the generators output and are unchanging
each cycle. The voice will cause all these other frequencies to vary
and thus be more "wide" spread than the test tone and the incoming
peak to peak voltages each cycle changing. It was always my
understanding that this is where the IMD problem came from. The two
tone test shows so much, but like you said, the voice signal may be
unmeasurable.
Measuring the IMD level of a voice signal involves setting up the A/B
VFOs c. 4.5KHz apart on a separate receiver. Set VFO A on-frequency.
Set VFO B 4.5KHz higher for a LSB IMD measurement, or 4.5KHz lower in
freq for a USB measurement. Switch to VFO A, say Ahhhhhh into the mic
and note the S-meter reading. Switch to VFO B, say Ahhhhh and note the
S-meter reading. If you know the db per S-unit calibration of the
S-meter, you then know how many db down the total IMD is.
However, I would like to know what it would be by using the different
regulators with voice modulation. After all, we don't speak in two
tones but all of them with differentiating volume. I'd still about bet
it will raise it.
Will Matney
"Multiple tones could also be used rather than just two tones but that
gets tough to unscramble as many more products are produced.
73
Gary K4FMX"
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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