Hi Lyle,
Thanks for your comments. Yes with NBVM, at the transmitter end, voice
frequencies above 1500 Hz were folded back (sideband reversal) into the
gap . The process was reversed in the receiver. As far as I remember,
Tom VE2AGF told me they even found it unnecessary to null out the middle
frequencies. I assume (shouldn't do that!) that the received processed
audio middle frequencies would contain both the high end vowel
frequencies with reverse sideband consonant frequencies. The reverse
sideband frequencies would dominate.
I don't think we even want to consider NBVM transmitting. There are
enough different modes now and a digital solution would be more
bandwidth efficient.
The contour (for want of a better name) approach does seem to help in
those situations where stations are spaced 1 kc apart. Using USB for
example, the station 1 kc lower will will have its high frequency
consonants mainly in the gap (null) of the receiving station. The middle
frequencies (low power unless heavily processed) will fall over the
vowel frequencies of the wanted signal. The station higher in frequency
will have its vowel frequencies at the high end of the gap and its
middle frequencies will be over the high consonant frequency band.
I have not had time to give it a good test. The noise reduction of the
narrower bandwidth is not significant but annoyance of the band noise in
the gap is eliminated. It is debatable whether the built in NR is better.
I think filter settings need to be set up with macros. Manual
adjustment in the heat of the battle is way too slow. I suggested before
that maybe the XFIL (or SPOT or CWT) which are not used on SSB could be
used for customizable filter settings (in sequence).
It does need a crowded band SSB contest style to give it a good test.
It will need fast switching for comparison. Set your filter macros in
the "K3 Utility" Command Tester.
73
Tony VE3QF
Lyle Johnson wrote:
The NBVM people took this a step further. Once the spectrum was
notched, they shifted the upper frequency range down by the notch width,
resulting in a narrower overall spectrum while maintaining intelligibility.
Ignoring the bandwidth for the moment, the question becomes, "Is the
resulting voice signal acceptable under crowded band conditions?"
73,
Lyle KK7P
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