[RTTY] Bandwidth of a RTTY signal (was:SO2R RTTY Radio)

[Kok Chen]

On Tuesday, August 28, 2001, at 01:17 PM, Ekki wrote:

> Indeed, 250Hz is
> working less good than 350Hz if the signal is noisy or has flutter.

Hi, Ekki,

By noisy signal, do you mean a badly modulated signal?  If it
is band noise or QRM, then using a wider filter should make the
signal-to-noise ratio worse, not better?

Also, does flutter also increase the bandwidth of an RTTY signal?
I am always curious what polar flutter really is.  Is it multiple arrival
time/phase of a signal?

Does anyone know if Rayleigh fading also broadens the FSK
spectrum appreciably?

I use two sets of filters on my 1000MP.  One is a 250 Hz/250 Hz
pair (both INRAD) and the other is a 400 Hz/500 Hz pair (the
400 Hz is INRAD, the 500 Hz is Yaesu).

For me print has invariably been better using the 250/250 pair.

Ditto with my FT-990.   I have a 250 Hz filter and a 500 Hz filter
on that rig,  The 250 Hz one always provides better copy with 170 Hz
Baudot.

Granted, these filters don't have infinite slopes, either :-).

> It get's worse when 200Hz shift are used, as it is unfortunately happing
> more and more because it's the standard shift for Pactor-1 and some TUs 
> use
> the same shift for all modes.

During the Slovenian contest, I only remember one station with a 200 Hz
shift.  I think the more widespread use of Sound Cards is actually a
help here.

73
Chen, AA6TY