This is very common amongst VHF/UHF weak signal DXers (including
EMEers) too.
It's also little know but wider bandwidths for SSB improve
intelligibility too especially for the very weak signal case (see the
graphs on articulation index versus bandwidth in Sabin's book on SSB).
The reason to use narrower filters is to reduce QRM that your brain
(or the RX) can't deal with.
Why do wider filters work:
1. It avoids the problem of impulse noise being smeared in time by
the limited bandwidth of the filter (and by group delay in the
filter) so in noisey environments a wider filter can help a lot.
2. Your brain is an interesting signal processor. It can act as a
very narrow (50Hz or so) adaptive filter but without the usual
problems of group delay and the like of a real filter.
It was mentioned in EMRFD and you can find it on VHF DXer websites
too. SM5BSZ comes to mind.
On Jun 16, 2007, at 6:19 AM, Jeff Frank wrote:
I almost always have easier and clearer copy on weak cw signals
when I use the 1.8 khz filter vs. the .5 or .25 khz filters in my
6.3 mhz IF. I've got nothing in the N1 position. Is this the way
it's suppposed to be?
--
73 DE N7WIM / G8UDP
Kevin Purcell
kevinpurcell@pobox.com
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