On 11/29/2013 6:25 AM, Joe Subich, W4TV wrote:
> My K3 copies RTTY fine through the 200 Hz filter.
This is much like the old ads "I worked 150 countries with my
Gotham vertical" ... When one tries to pass a FSK signal through
a "too narrow" filter it doesn't just stop working. However, the
tight skirts of the filter cause the energy in the mark and space
channels to smear (pulse stretching) into the next bit period and
cause errors in decoding.
Yes. Those of us who worked extensively in pro audio in the last 30 or
so years are well aware of the significance of the phase response of
filters and systems. We learned, for example, that varying amplitude
response has an associated variation in the phase response. Thus, I was
quite wary of using the "double humped" response provided by the K3
Quoting from W7AY's website, "With a software demodulator that includes
a matched filter or a raised cosine filter that matches the baud rate of
the RTTY signal, the receiver's filter should be only as narrow as
needed to keep interference from clipping the sound card. "
David Wicks, G3YYD, author of the new and highly regarded RTTY decoder
called 2Tone, advises use of a filter no narrower than for RTTY
decoding. I was not at all surprised to read it in his documentation.
73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
