[RTTY] K3 RTTY bandwidth already too narrow?

[Ed Muns]

An IF bandwidth of 400 Hz is about optimum for most RTTY decoders to do the
best job they are designed to do.  This is true for single signals in
sub-optimal conditions like flutter, fading, multi-path, etc.  Even in
lighter QRM situations, a good RTTY decoder needs 400 Hz to do its best job.

However, with very loud close-by signals (often found in contests) which
severely hammer the receiver RF/IF and AGC, a better overall trade-off may
be narrower IF filtering.  Anecdotally, I've gone as low as 200 Hz in some
situations, but most of the time copy is better at 300-400 Hz.

Keep in mind that multiple IF filters cascade to a narrower effective IF
bandwidth.  In the K3, a 400 Hz crystal filter plus a DSP bandwidth of 400
Hz will be nearly 300 Hz.  In the older Yaesu radios that had 250 Hz INRAD
crystal filters in each IF, the actual crystal filters were about 370 Hz so
that the two cascaded IF filters resulted in 250 Hz bandwidth for the radio.
I suppose it was easier to call both filters "250 Hz" rather than expect
users to do the math with the actual bandwidths.

Ed W0YK


> ORIGINAL MESSAGE: 
> On Sat, 23 Mar 2013 16:15:17 -0400 (EDT), K9OM wrote:
> 
> > (though I prefer to use my 400hz
> >roofing filter with a 400hz DSP setting as it copies signals better)
> 
> W6WRT REPLY: 
> My experience has been that 400 Hz is a bit wide for RTTY 
> during a contest.
> Try 300 and see if that helps things.