[Elecraft] RTTY and filters

[J. Edward (Ed) Muns]

> I previously mentioned in an email to the group that I was looking forward
> to trying out the 200hz filter in my K3 for RTTY contesting.  I had one
> reply wondering if that filter was going to be too tight for RTTY.
> 
> Any comments from the group on this.
> 
> The other person that emailed was planning on using the 400hz filter.

I only operate RTTY with narrow filtering, all of the following
simultaneously in the K3:

- 250Hz crystal filter
- 200Hz DSP filter
- Dual-Tone Filter

In the 756ProIII, I use the 250Hz RTTY DSP filter and the Twin-Peak Filter.
The only roofing filter "choice" in the ProIII is the standard 15kHz,
although the INRAD 4-5kHz can be added.

I want the filtering as tight as I can get it so the RTTY decoders have the
best chance to do their job.  Stations need to be good at zero-beating,
which is easy in RTTY because your decoder display is a perfect tuning
indicator.  Alternatively, on my side I have to ride the RIT a lot to pull
in the off-frequency signals.  This weekend there were a lot of stations
calling off frequency, some as much as 200 Hz away.  I suspect that those
using AFSK with AFC were responsible for a lot of that.  In other words,
their receiver was zero beat with me but their "smart" encoder skewed their
Mark tone away from where they were receiving.

In a sense these off-frequency folks are helpful because they don't QRM the
ones who are zero beat with me!  Once I work the zero-beaters out of the
pile-up, then I can grab the others with the RIT ... if they're still there.

73,
Ed - P49X (W0YK)