Alan Bloom wrote:
The problem is that different RTTY transmitters use different amounts of
filtering. However I suspect that a "Nyquist" receive filter designed
to compensate a typical/average transmit filter probably would have
pretty good performance on most received signals. Does anyone know if
this has ever been tried?
With digital filters, one ought to be able to use the sort of adaptive
filters used in modems, where the filter coefficients are adjusted by
comparing the actual signal against the expected signal. Modems send a
known training signal, to get fast initial convergence, but if the
signal is at least marginally decodable, I would have though it would be
possible get the filter to converge. One could probably start by making
assumptions about the transmit filter and using known information about
the receiver.
This tactic will work better for synchronous systems, like PSK, but I
would have thought it must be possible to train a filter off an
asynchronous signal as well, although one might have solve for the
signalling unit centre position after receiving the whole character.
--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
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