RTTY
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Re: [RTTY] RTTY Rx filter bandwidth

To: "RTTY reflector" <rtty@contesting.com>
Subject: Re: [RTTY] RTTY Rx filter bandwidth
From: "Dave Hachadorian" <k6ll@arrl.net>
Reply-to: Dave Hachadorian <k6ll@arrl.net>
Date: Thu, 10 Jan 2013 11:00:00 -0700
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
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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