[Elecraft] RTTY filter for K3

[David Woolley (E.L)]

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
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