[RTTY] 250 hz filter on RTTY

[Robert Chudek - K0RC]

Rick,

I agree with Phil regarding the 250 Hz filter. You will definitely need this selectivity on 20m when a full-fledged contest is running! In the past I would turn this narrow filter on occasionally, only when I needed it. During the 2006 ARRL RTTY I don't think I ever turned it off! RTTY contesting really seems to have caught on recently!

Regarding the external audio filters, this depends on your RTTY demodulator. Using a KAM, AEA, or MFJ (hardware) TNC, an external unit might help. But if you're using MMTTY, the filters available in that product do an excellent job. You can customize them to whatever bandwidth you desire. And to top it off, you can preview the audio bandwidth characteristics on a graph.

The downside to the MMTTY internal audio filters is YOU do not benefit from their steep skirts. With your speaker connected to the transceiver audio output, you will continue to hear the normal rubbish on a crowded band. I suppose you could drive your speakers from the soundcard output, but I haven't tried that so I don't know if that would work or not.

73 de Bob - K0RC


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Message: 7
Date: Tue, 23 May 2006 10:35:37 +0100
From: "pcooper" <pcooper at guernsey.net>
Subject: Re: [RTTY] 250 hz filter on RTTY
To: Rmintz at Rochester.rr.com
Cc: RTTY at contesting.com
Message-ID: <1148376937.864ccf00pcooper at guernsey.net>
Content-Type: text/plain; charset="UTF-8"

Hi Rick and the group,

I am sure you will find the 250Hz filter just fine, and maybe even a little wide at times.

OK, I know the filtering on a 756Pro is a little different, but I frequently set my filters down to 100Hz. Whilst that may seem very narrow, I don't use the built in RTTY filters, as I prefer to change mine according to needs at the time.
The filtering in this way is a little SSB-like, in that the skirts flare out enough to give copy on a RTTY signal when set to 100Hz.
It will even cope with those signals that are slightly wider than usual, but you do have to tune in the signal very accurately.

So, I am sure you will find 250Hz just fine!
It may also pay you to look out for one of the external audio filters that sit between the rig and the soundcard. These can clean up a lot of hash, and make copy a little more reliable.

Cheers for now

Phil GU0SUP