[Elecraft] K3 SSB Contour Filter (reduce total bandwidth)

[Tony Fegan VE3QF]

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