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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