I use the 250 Hz roofing filter and DSP BW 350 as my go-to RTTY
settings on the K3. It seems to work well for me. Use the SHIFT
control to make sure the mark and space are centrally spaced in
the spectrum display. The mark and space should be just about
the same amplitude as the center amplitude, with the sidebands
tailing off on both sides from there.
Dave Hachadorian, K6LL
Yuma, Arizona
-----Original Message-----
From: RLVZ@aol.com
Sent: Thursday, January 10, 2013 10:19 AM
To: lists@subich.com ; rtty@contesting.com
Subject: [RTTY] RTTY Rx filter bandwidth
Wow- a lot of terrific RTTY information on this Reflector!
I agree with Joe that "400 Hz is nearly the minimum bandwidth
necessary
for proper decoding". When contesting under heavy QRM condx, I
try and try
and try using the 250hz roofing filter in my K3 to reduce
adjacent channel
interference and the radio simply does not decode the average
RTTY signal as
well as the 400hz roofing filter does. By the way, when using
the 250hz
roofing filter I have the DSP filter set to 350hz. I've been
told that the
K3's 250hz roofing filter has a bandwidth of aprx. 370 hz... so
I thought
these 2 settings would provide for maximum selectivity and RTTY
decoding...
but that simply is not the case as when I switch over to the
400hz roofing
filter the copy on the average RTTY signal is significantly
better.
Perhaps someone has found a better overall RTTY receive filter
combination for
the K3 than my settings of: 250hz roofing filter with 350hz DSP
filter?
Such as, perhaps the 250hz roofing filter with the DSP filter
set to 400 or
450hz?
73,
Dick- K9OM
400 Hz is nearly the minimum bandwidth necessary for proper
decoding
(minimum intersymbol interference). Narrower filters work by
cutting
adjacent signals more than the desired signal but they impose a
much
higher group delay than a filter that is "flat" across the
necessary
350 to 370 Hz bandwidth.
73,
... Joe, W4TV
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