Axel
I was the first to respond to your question. I told you that I was listening
to RTTY through the 200 Hz, 5 pole filter and it worked fine. Then the
experts came on here and using many words, explained why it couldn't work
because it is too narrow. Maybe they do not actually have the filter but I
do.
Looking at the waterfall on MixW, 200Hz filter engaged, a RTTY signal easily
fits within the waterfall's passband with a little room on either side. The
vertical stripes of the RTTY signal do not quiet reach the outer edge of the
waterfall which tells me that the "data" is not being chopped off. Both weak
and strong RTTY signals seem perfectly copyable.
No I would not use this in a contest unless I had a bandscope so I could
find signals. I have ordered the LP-PAN which should take care of that
little detail.
73
Steve Ellington
[EMAIL PROTECTED]
----- Original Message -----
From: "Axel Kaiser" <[EMAIL PROTECTED]>
To: "Elecraft Reflector" <elecraft@mailman.qth.net>
Sent: Sunday, May 18, 2008 4:14 AM
Subject: [Elecraft] RTTY filter for K3
To all you filter aficionados,
first of all thank you very much for all your detailed answers to my
original question, which roofing filter ist best for RTTY operation of the
K3. Lots of very detailed and informative answers were given and even a
general discussion on this issue among several others was started. But to
tell you the truth, I am still somewhat uncertain, which filter to order
with my K3.
One of my theory books about HF technology, modulation, bandwidth and so
forth, tells me, that the necessary bandwidth for a 170 Hz shift RTTY signal
should be around 320 Hz. Now some of you guys write, that you are using a
250 Hz filter for RTTY operation. A 250 Hz filter though has this 250 Hz
(ok, a few Hz more in reality) bandwidth at - 6dB attenuation, which means
that the actual bandwidth at about 0 db is even less.
So my understanding for a 170 Hz shift RTTY operation is, to use a filter of
at least 400 - 500 Hz (at -6dB) in order to get all the information through
the filter. This I can confirm also with my current OMNI VI+ which does not
allow me to copy RTTY signals with a 250 Hz filter . So please, where is the
point which I am missing with the K3, that you can work weak RTTY signals
with a 250 Hz roofing filter??
Best 73 de
Axel, DL3ZH
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