I've use the narrow filters (250Hz) on PSK31 with excellent results.
As to S/N improvement, cut the bandwidth from 500 Hz to 250 Hz and
automatically you get a 6dB improvement in S/N.
As to stability, the Omni VI+ with either the oven time base or the TXO/TCO
combination is more than adequate for PSK31. Typically I follow the Omni
with a DSP filter of 100 Hz for my EME operations. That gets another 6 dB
S/N improvement.
Today's new radios typically move around something like 10 Hz to 50 Hz
depending on temperature and voltage. That's no problem for 100 Hz filters.
Older tube type radios......well we were lucky to keep them in the band.
One brand is affectionally known as "driftometers" (pronounced kinda like
speedometer) HI
73
Bob K4TAX
----- Original Message -----
From: <ditzian@alltel.net>
To: <Tentec@contesting.com>
Sent: Friday, January 04, 2002 12:05 PM
Subject: Re: [TenTec] Next filter?
> I have followed the thread about narrow filters with interest, but I
> note that no one has mentioned using very narrow filters on
> PSK31. The theoretical bandwidth of this slow mode is 50 Hz.,
> and I do not know if the ringing would bother PSK decoding. I
> would love to try 100 Hz. filters in my Omni VI, or even the 250 Hz.
> filters, except I am too cheap to purchase them. I expect that the
> effectiveness of this combination will be evaluated by someone
> using IF DSP, when a manufacturer finally includes extremely
> narrow filters.
>
> There is the question of whether there is a meaningful increase in
> S/N using extremely narrow filters. Of course, there may be a
> problem with drift and losing the other guy, unless both stations are
> using extremely stable VFOs, and I do not know if the Omni VI
> would suffice here.
>
>
> 73,
> Jan Ditzian
> KX2A
> kx2a@arrl.net
>
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