Bill,
Sorry, with due respect... My personal experience is just opposite.
I used to use a chain of 2 x 250 Hz filters in an IC-756 "Classic". I can
clearly recall World Top Ten in WPX RTTY SB 20 m at least 2 times in a row
among other results. You can judge yourself how significant this experience
is.
I have no idea what actual passband the 2 filters in series provide in real
life (I did not measure it), but for sure there were 2 x 250 stock Icom
filters and I did not have any problems with decoding. There was an
exception, to tell the complete truth. Some 10-15 years ago we could still
meet the 200 Hz shift signals which were indeed too wide for the 2 filters
in series. To decode such signals, I had to switch off one of the filters.
73,
Vladimir VE3IAE
---
-----Original Message-----
From: RTTY [mailto:rtty-bounces@contesting.com] On Behalf Of Bill Turner
Sent: Sunday, August 25, 2013 5:20 PM
To: RTTY Reflector
Subject: Re: [RTTY] 300hz or 500hz IF filter?
ORIGINAL MESSAGE: (may be snipped)
On Sun, 25 Aug 2013 11:09:19 -0700, Chen wrote:
>The 1.2 factor is purely empirical. But if you follow the ITU formula
>religiously, steam RTTY comes out as having a bandwidth of
>249.45 Hertz.
REPLY:
Why would anyone follow a formula that doesn't work in the real world?
Any RTTY operator with any significant experience knows that a bandwidth of
exactly 249.54 Hz will not work. The print will be just garbage. The actual,
true, honest bandwidth has to incorporate more spectrum than that or you are
just wasting your time. Don't be fooled by what someone calls a "250 Hz"
filter. If it actually works, it's letting more spectrum through than that.
Long experience has shown that around 300-350 Hz on the typical ham receiver
works. Less does not.
Can we at least agree on that?
73, Bill W6WRT
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