[RTTY] RTTY Rx filter bandwidth

[Dave Hachadorian]

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 at aol.com
Sent: Thursday, January 10, 2013 10:19 AM
To: lists at subich.com ; rtty at 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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