[RTTY] 300hz or 500hz IF filter?

[Bill Turner]

ORIGINAL MESSAGE:          (may be snipped)

On Thu, 22 Aug 2013 21:42:05 -0400, Kai wrote:

>
>The theoretical bandwidth of 170 Hz shift 45.45 baud RTTY is just under 250 Hz.
>73
>Kai, KE4PT

REPLY:

Not so. The "theoretical" bandwidth of ANY FM signal is infinite. The
sidebands extend out forever. Check any book on FM theory, such as the ARRL
Handbook. 

That is why it is pointless to talk about "theoretical" bandwidths. You only
need enough bandwidth to reproduce the transmitted signal without "rounding
off" the corners too much. How much is too much? There is no precise answer
and that is why talking about "theoretical" bandwidth is a waste of time. 

Long experience has shown that a traditional amateur RTTY signal needs about
300-350 Hz bandwidth with a typical ham receiver. You can get that with a
narrow filter with wide skirts or a wide filter with narrow skirts. When you
have the correct bandwidth for your receiver, increasing it does not improve
reception. That's the real test.

73, Bill W6WRT