[RTTY] Re: Noise with MMTTY

Bill Turner wrt at dslextreme.com
Wed Mar 24 07:46:59 EST 2004

On Tue, 23 Mar 2004 13:19:23 -0600, Don Inbody wrote:

>As far as an RTTY signal, I don't believe the sound detection circuit is
>that smart, but I do believe that when one cranks the filters down too hard,
>one actually loses part of the signal (outlying tones) and that makes it
>more difficult to copy under noisy conditions. 


Quite correct.  RTTY is a form of FM (think of a carrier being frequency
modulated by a square wave) and as such, it has sidebands.  For a 170 Hz
shift, a filter width of about 250 Hz would be correct, but if your
filter has extremely steep skirts, widening it out might help, provided
there is no nearby QRM.

RTTY at first glance seems to be a simple mode, but not really.  :-) 

Bill, W6WRT
QSLs via LoTW

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