wrote:
>Ian:
>??????I read your description of the GW4RFX measurments, which strike
>me as being a quite practical approach to estimating splatter. Yes,
>this procedure could readily be codified and performed with modern
>analyzers (especially programmable ones.)
>
>??????Intuitively, this measurment procedure seems to fulfill our need
>to evaluate the amount of crap that many of us are subjected to on a
>daily basis by selfish stations and operators (it isn't just the big
>amps - I regularly receive signals from stations with very high
>performance anternnas that go well into the red on my S-meter, and
>parking within 10khZ of one of them can be futile.)
>
>??????I would also be an advocate of such a paradigm for this difficult
>measument issue. But before warming up my analyzer, I would like to
>pose one question which addresses the potential value of this. That is,
>how does this test(s) result that he obtained by such averaging compare
>with standard two tone tests in situ? Let me be a bit more specific.
>
>??????My suspicion (that means somewhere between an 'opinion' and a
>'fact') is that if standard two tone tests were performed, using a few
>different audio frequencies and applying some weighting/averaging rule
>to them, were applied to the same setup, there would be a large
>correlation with the referenced results. I would like to see that done
>(maybe it has and the news just hasn't arrived here yet.) as a
>qualification for or against the spectrally averaged method as
>proposed.
I don't think that the frequencies alone is enough. You'd also have to
vary the amplitudes at each frequency... and then the test protocol
starts to become messy.
The other point that hasn't been mentioned (this time around) is that a
speech signal is has frequency components at maybe 300-2000Hz, but also
at syllabic and word rates of around 1-10Hz. This low-frequency peak in
the signal frequency spectrum is what really tests the regulation of the
power supply. You don't see it in static two-tone tests - even a very
poorly regulated power supply can look good when nothing is changing.
These added complexities are the reason why, if you're going to move
away from static two-tone testing, it's best to go all the way to a
real-life speech signal. (One of the advantages of "peak hold" testing
with a standard digital signal file is that it can include several
different kinds of voices - you just have to run the test a little
longer.)
On the other hand, some work does need to be done on comparing the
results of static two-tone tests with those of peak-hold speech tests. I
don't think you would find much correlation at all... but it would
clearly demonstrate the failings of the older test.
On the other-other hand, if the FCC have already adopted such a test,
there must already be some published technical justification. We ought
to try to find that first.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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