[Lf] CW filter

[Frank Gentges]

Hi,

Those who have sat through my rantings the past two weeks at tacos knows 
that I want a good CW filter to go with the LF receiving setup we have 
been evolving with the RX320 and spectran.  Tonight I had a chance to 
revisit Hamview which is the predicesor of Spectran.  It uses full duplex 
sound card capability to send processed sound out of the analysis program 
while at the same time receiving sound from the receiver.

A feature of Hamview is to put markers for a bandpass filter upper and 
lower limits.  It also has a feature where you can have a narrow CW 
filter by setting its frequency either automatically or visually with the 
mouse.  

After our trip and experience with Nags Head I have developed a better 
understanding of what is needed.  I now find the Hamview filter functions 
really close to the mark.  I was able to extract DCH and TH here tonight 
when they were buried in the noise with the 300 Hz RX320 filter.  The 
ergonomics of the Hamview setup work really well as I move around and 
when a line is seen on the spectrogram I can point-and-listen with ease.

Hamview seems to have enough selectivity to meet our needs for now but of
course we have the sound card compatibilty problem with notebooks and SB
clones.  

Spectran differs from Hamview by providing more selections of spectrogram
bandwidths going ever narrower.  As we develop narrower bandwidth
signaling modes Spectran will meet our needs better than Hamview.  I would
assume the CW filter would similarly track the spectrogram bandwidth,
seems reasonable. 

Now if we crank down the bandwidth to say 0.032 Hz we could see a channel 
time response of 1/.032 = 31.25 seconds.  That would imply a maximum code 
speed of about 30 second dots and thus 3x30 = 90 second dashes.

I have a hard time imagining copying code aurally at this rate let alone 3
second dots.  I am not sure what I would want in this instance.  Can
someone think up a rational reason for what we would want and why? 

I would like to stimulate a little discussion on this as I start thinking 
about what Spectran will become.  A separate DSP CW filter may not add much.

Frank K0BRA