Joe is correct on the calculated characteristics of cascading filters.
An additional consideration is actual on-air circumstances that you will
encounter while working a RTTY contest. Stations pack themselves into the
available spectrum tighter than a can of sardines. This was the case last
weekend with the huge participation in the CQWW WPX RTTY contest.
What you will find in this environment is one fellow calling you that is +20
dB over S-9 but there's another station that is calling someone else, maybe
200 Hz away. His signal is also +20 dB over S-9. This would be the situation
where Joe says "some [RTTY operators] use them [250 Hz filters] and accept
the additional loss".
That would be me and the majority of RTTY contesters. I will accept a 6 dB
loss on the desired signal if I can attenuate the other station by 20, 30,
or 40 dB. It can mean the difference whether you can copy the guy on your
frequency or not.
Outside of contesting, when stations have plenty of room to spread out,
using 250 Hz filters is not a critical tool that will make or break a
contact. The wider bandwidth will reduce the chance of decoding errors
because you are not "giving up" part of the signal.
73 de Bob - KØRC in MN
----- Original Message -----
From: "Joe Subich, W4TV" <lists@subich.com>
To: "'David VE3VID'" <ve3vid@hotmail.com>; "'RTTY contest group'"
<rtty@contesting.com>
Sent: Thursday, February 18, 2010 5:48 PM
Subject: Re: [RTTY] Kenwood IF filters ???
> Is my logic correct? RTTY signals are "supposed" to
> be 170hz wide, so a 250hz filter would be optimal......
> yes/no.......(circle one hihi)
No. The RTTY shift is 170 Hz but there are keying
sidebands that are necessary to proper decoding. As
a rule of thumb you can add the shift plus three times
the baud rate to get the bandwidth of an FSK signal.
For 45.45 baud/170 Hz shift RTTY that works out to just
about 300 Hz. Since the cascaded 250 Hz filters are
supposedly -6dB at 250 Hz, that makes them just a bit
too narrow for RTTY (although some use them and accept
the additional loss). Cascaded 400 Hz filters would
be better on a theoretical basis ... both tones and
the keying sidebands will be within the "flat" part
of the filter response and not down on the skirts.
73,
... Joe, W4TV
> -----Original Message-----
> From: rtty-bounces@contesting.com
> [mailto:rtty-bounces@contesting.com] On Behalf Of David VE3VID
> Sent: Thursday, February 18, 2010 4:30 PM
> To: RTTY contest group
> Subject: Re: [RTTY] Kenwood IF filters ???
>
>
>
>
>
> Hmmmm ??? Okay. I am using MMTTY. WPX last week was my
> first contest. I wasn't aware MMTTY did filtering. My
> TS-450s has the stock filters for SSB: 6khz in the 8.83mhz
> passband an 2.4khz in 455khz IF. Obviously those filters are
> frustrating for RTTY.
>
> Show of hands please from users with TS-850s & TS-450s - 2 x
> 400hz filters for both IF stages, or 2 x 250hz filters in
> both. Is my logic correct? RTTY signals are "supposed" to
> be 170hz wide, so a 250hz filter would be
> optimal......yes/no.......(circle one hihi)
>
> Al (KE1FO) - why did you find the narrow filters frustrating?
> Can you comment on "MMTTY filtering"?
>
> David
> VE3VID
>
>
>
> > Date: Thu, 18 Feb 2010 12:57:29 -0500
> > Subject: Re: [RTTY] Kenwood IF filters ???
> > From: al@frugoli.info
> > To: ve3vid@hotmail.com
> >
> > Be careful. 400 is often as narrow as you wat to go, especially if
> > you're contesting. I find that the filtering MMTTY can do
> is adequite
> > in 99% of the cases with a 400hz filter.
> >
> > The TS940 I used to use had a 250 filter and it was
> frustrating when
> > trying to s&p during contests.
> >
> > 73 de AL, KE1FO
> >
> > On 2/17/10, David VE3VID <ve3vid@hotmail.com> wrote:
> > >
> > > Thanks for the Inrad URL Jim..........the 250hz filters
> would likely
> > > be exactly what I need
> > >
> > > :)
> > >
> > >
> > >
> > > David
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Date: Tue, 16 Feb 2010 14:55:23 -0800
> > > From: w6eu@sbcglobal.net
> > > To: ve3vid@hotmail.com
> > > Subject: Re: [RTTY] Kenwood IF filters ???
> > >
> > > http://www.inrad.net/home.php?xid=369e20e231649e0ad9497f17437841f8
> > >
> > > Try this website, David
> > >
> > > 73, Jim W6EU
> > >
> > >
> > > David VE3VID wrote:
> > > What is "Inrad".........a manufacturer? Do you know where
> they are
> > > available?
> > >
> > >
> > >
> > >
> > >
> > >
> > > From: ww3s@zoominternet.net
> > > To: ve3vid@hotmail.com
> > > Subject: Re: [RTTY] Kenwood IF filters ???
> > > Date: Tue, 16 Feb 2010 17:38:03 -0500
> > >
> > > I have an 850, but the filters are the same....I use a
> set of 400 hz
> > > Inrad in both IFs....
> > >
> > > On 2/16/2010 5:36:25 PM, David VE3VID (ve3vid@hotmail.com) wrote:
> > >
> > >
> > >
> > > Are you working RTTY with a Kenwood TS-450s? Which of the
> optional
> > > IF filters do you use? There are filters for the 455khz
> and 8.83mhz
> > > passbands. Which would work best for RTTY. I've done a
> little bit of
> > > RTTY without the filters just to cut my teeth, but the narrow IF
> > > filters are obviously necessary.............any infor would be
> > > appreciated.
> > >
> > >
> > >
> > > David
> > >
> > >
> > >
> > > VE3VID Located in rural Canada
> > > Solar power. Wood heat.
> > > Mosley tribander @ 22m
> > > 2element delta-quad on 40m
> > > Lots of space for dipoles,
> > > bears and wolves......73
> > >
> > > http://www.ve3vid.webs.com/
> > >
> > >
> > >
> > > _________________________________________________________________
> > >
> > > _______________________________________________
> > > RTTY mailing list
> > > RTTY@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/rtty
> > >
> > > _________________________________________________________________
> > > Introducing Windows® phone.
> http://go.microsoft.com/?linkid=9708122
> > > _______________________________________________
> > > RTTY mailing list
> > > RTTY@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/rtty
> > >
> > >
> > > _________________________________________________________________
> > > Introducing Windows® phone.
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> > >
> >
> > --
> > Sent from my mobile device
> >
> > 73 de Al, KE1FO
> >
> > -----
> > Check out my Amateur Radio Contesting blog at ke1fo.wordpress.com.
>
>
>
> All your Hotmail contacts on your phone. Try it now.
>
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