Current thinking is to use a fairly wide filter for RTTY. The
software filters that are applied in the sound card are much
narrower, about 50 Hz wide. Lately I've been using the 2.7 KHz
roofing filter, with DSP bandwidth set to about 600 Hz.
Dave Hachadorian, K6LL
Yuma, AZ
-----Original Message-----
From: Mike Dodd
Sent: Tuesday, April 12, 2016 8:03 PM
To: elecraft@mailman.qth.net
Subject: [Elecraft] K3s AFSK frequencies
Hello to the group. I just put my new K3s/100 into service, and
have a
question about the Mark frequency to use with AFSK. Before the
K3s, I
used a SignaLink with my KX3 and MMTTY. With that setup, I set
MMTTY to
use 915 Hz for the Mark frequency, and everything worked fine.
Fiddling with the K3s and its internal USB sound card (I love
that!), I
can select various higher Mark frequencies using the PITCH
button, and
set MMTTY accordingly, and the K3 still decodes the RTTY.
So my question is, what is the "standard" or common Mark
frequency to
use for AFSK on the K3? Or is it a matter of personal
preference --
which sounds better to my ears when tuning RTTY signals?
Also, what bandwidth is commonly used for 170 Hz-shift RTTY? I
stocked
this K3s with four 8-pole filters, including 400 Hz and 250 Hz.
The 250
Hz filter works with RTTY, but the MMTTY X-Y scope pattern looks
like I
might be pushing things with that narrow a filter. the 400 Hz
filter
looks better.
But David (I think) at Elecraft told me when I made my list of
filters
that I'd be using 2.1 kHz or 2.8 kHz for RTTY. That doesn't make
a lot
of sense to me if QRM is present. OTOH, MMTTY is decoding
specific
tones, so maybe filter width doesn't make much difference.
What do the experts say?
Thanks for any information.
--
73, Mike N4CF
Louisa County, VA USA
Elecraft K3s/100
Carolina Windom up 45'
http://n4cf.mdodd.com
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