[RFI] IN-band Filters

Bryan Swadener bswadener at yahoo.com
Tue Nov 7 20:00:14 EST 2006

> >  I'm looking for some form of filter for the
> purpose of 
> > reducing interference between stations operating
> on the 
> > same band (ie, fone-cw).  This would be used in a
> planned 
> > multi-transmitter contest setup during Field Day
> 2007. 
> > The bandwidth and slope would need to be good
> enough to 
> > prevent fundamental overload of (and possibly
> damage to) 
> > the receiving station.
> You typically won't be able to have significant
> attenuation 
> even with very good L/C components and stubs with
> their 
> inherent low Q are out of the question.
> I was somewhat successful using toroids with a Q
> unloaded of 
> 500 or so in a well designed filter, but tuning of
> the 
> filter was critical.  Stubs actually have terrible
> Q, 
> especially down on 80 or 40 meters.
> The real key is antenna separation and good radios.
> 73 Tom 

Tom & Tim,

Thanks for the quick replies.  In the interest of
maintaining Q, I have access to tight tolerance
porcelain (very low ESR) capacitors and up to #10
polyimide-coated wire.  However from your experiences,
it sounds like my idea would be wasted effort.

We'll use your suggestions: wide antenna separation +
good radio equipment.  We have use of a site that will
allow up to about 1000' separation.  We plan on using
an Elecraft K2 and a Yaesu FT990.

Vy 73,

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