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RTTY and filters

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w0mu

RTTY and filters

I previously mentioned in an email to the group that I was looking forward
to trying out the 200hz filter in my K3 for RTTY contesting. I had one
reply wondering if that filter was going to be too tight for RTTY.

Any comments from the group on this.

The other person that emailed was planning on using the 400hz filter.

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Jerry Flanders

Re: RTTY and filters

I plan to use the 400 Hz roofing filter combined with 250-350 Hz DSP
filters for 170 Hz shift RTTY. I have used 250, 300, and 350 Hz DSP
filters with ICOM 756PRO series radios for years with success.

Jerry W4UK

At 01:28 PM 1/7/2008, you wrote:

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Ed Muns, W0YK

RE: RTTY and filters

In reply to this post by w0mu

> I previously mentioned in an email to the group that I was looking forward
> to trying out the 200hz filter in my K3 for RTTY contesting. I had one
> reply wondering if that filter was going to be too tight for RTTY.
>
> Any comments from the group on this.
>
> The other person that emailed was planning on using the 400hz filter.

I only operate RTTY with narrow filtering, all of the following
simultaneously in the K3:

- 250Hz crystal filter
- 200Hz DSP filter
- Dual-Tone Filter

In the 756ProIII, I use the 250Hz RTTY DSP filter and the Twin-Peak Filter.
The only roofing filter "choice" in the ProIII is the standard 15kHz,
although the INRAD 4-5kHz can be added.

I want the filtering as tight as I can get it so the RTTY decoders have the
best chance to do their job. Stations need to be good at zero-beating,
which is easy in RTTY because your decoder display is a perfect tuning
indicator. Alternatively, on my side I have to ride the RIT a lot to pull
in the off-frequency signals. This weekend there were a lot of stations
calling off frequency, some as much as 200 Hz away. I suspect that those
using AFSK with AFC were responsible for a lot of that. In other words,
their receiver was zero beat with me but their "smart" encoder skewed their
Mark tone away from where they were receiving.

In a sense these off-frequency folks are helpful because they don't QRM the
ones who are zero beat with me! Once I work the zero-beaters out of the
pile-up, then I can grab the others with the RIT ... if they're still there.

73,
Ed - P49X (W0YK)

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Jerry Flanders

RE: RTTY and filters

I just checked the filter plot at http://www.elecraft.com/ . Strange
that they call it a 250 Hz filter because -6 dB BW is actually 370
Hz, compared to 435 for the 400 Hz filter. At -60, the "250" is 785
Hz wide, compared to 935 for the "400" one.

IOW, the 250 should pass all the 170 shift sidebands OK, because it
is not really that narrow. Not really much difference between the 250 and 400.

Jerry W4UK

At 02:20 PM 1/7/2008, J. Edward (Ed) Muns wrote:

> > I previously mentioned in an email to the group that I was looking forward
> > to trying out the 200hz filter in my K3 for RTTY contesting. I had one
> > reply wondering if that filter was going to be too tight for RTTY.
> >
> > Any comments from the group on this.
> >
> > The other person that emailed was planning on using the 400hz filter.
>
>I only operate RTTY with narrow filtering, all of the following
>simultaneously in the K3:
>
>- 250Hz crystal filter
>- 200Hz DSP filter
>- Dual-Tone Filter
>
>In the 756ProIII, I use the 250Hz RTTY DSP filter and the Twin-Peak Filter.
>The only roofing filter "choice" in the ProIII is the standard 15kHz,
>although the INRAD 4-5kHz can be added.
>
>I want the filtering as tight as I can get it so the RTTY decoders have the
>best chance to do their job. Stations need to be good at zero-beating,
>which is easy in RTTY because your decoder display is a perfect tuning
>indicator. Alternatively, on my side I have to ride the RIT a lot to pull
>in the off-frequency signals. This weekend there were a lot of stations
>calling off frequency, some as much as 200 Hz away. I suspect that those
>using AFSK with AFC were responsible for a lot of that. In other words,
>their receiver was zero beat with me but their "smart" encoder skewed their
>Mark tone away from where they were receiving.
>
>In a sense these off-frequency folks are helpful because they don't QRM the
>ones who are zero beat with me! Once I work the zero-beaters out of the
>pile-up, then I can grab the others with the RIT ... if they're still there.
>
>73,
>Ed - P49X (W0YK)
>
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Joe Subich, W4TV

RE: RTTY and filters

In reply to this post by w0mu

Mike,

My concern is that the 200 Hz filter might be too tight.
With 170 Hz shift and 45.45 baud, the minimum bandwidth would
be around 225 Hz (right at the rated - 6dB point of the "200
Hz" filter) and probably closer to 310 Hz to maintain some of
the "sharpness" of the shift.

Lyle or one of the other DSP folks would know the minimum
necessary bandwidth better that I do. However but since the
200 Hz roofing filter is not selected until the DSP bandwidth
200 Hz or less it would be safe to suggest that a full 200 Hz
configuration might be a little "too tight."

I would think the "250 Hz" filter with its 370 Hz -6 dB
bandwidth or even the 400 Hz filter with its 455 Hz -6 dB
bandwidth would be more appropriate roofing filters for
RTTY than the 200 Hz filter.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Mike
> Fatchett W0MU
> Sent: Monday, January 07, 2008 1:29 PM
> To: Elecraft Discussion List
> Subject: [Elecraft] RTTY and filters
>
>
> I previously mentioned in an email to the group that I was
> looking forward to trying out the 200hz filter in my K3 for
> RTTY contesting. I had one reply wondering if that filter
> was going to be too tight for RTTY.
>
> Any comments from the group on this.
>
> The other person that emailed was planning on using the 400hz
> filter.
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

Tom Hoedjes

Re: RTTY and filters

In reply to this post by w0mu

Depends on what you are up to.

For S and P with a soundcard 200 Hz sounds to tight.
The signals have a 170Hz shift and many stations still work with a 200 Hz Shift.

I used the standard filter narrowed down to aprox 700 Hz. Was OK for me
When some qrm comes up, switching to the 400 Hz filter

For Cq-ing your qso partner have to be exact on QRG with the 200 Hz filter but eliminates all others..
It is a matter of what are you looking for..

73 de Tom
HB9DOD KL5X
-------- Original-Nachricht --------
> Datum: Mon, 07 Jan 2008 11:28:33 -0700
> Von: Mike Fatchett W0MU <[hidden email]>
> An: Elecraft Discussion List <[hidden email]>
> Betreff: [Elecraft] RTTY and filters

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