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Re: [CQ-Contest] Bandpass Filters

To: CQ-Contest@contesting.com
Subject: Re: [CQ-Contest] Bandpass Filters
From: "Ethan Miller K8GU" <ethan@k8gu.com>
Date: Fri, 19 Oct 2007 16:33:56 -0500
List-post: <mailto:cq-contest@contesting.com>
Like John said, the W3NQN filters are the top of the pile.  I've done
some measurements with a network analyzer (HP 8753D) comparing the
three different kinds.  I can summarize them like this:

W3NQN > Dunestar > I.C.E.

I only had access to a few of the filters when I did this.  I have a
plot comparing the several Dunestar and I.C.E. filters to a modified
W3NQN design provided to me by N0FP on my web site:


I want to say that I've heard that someone did a much more thorough
comparison in SMC's Blackhole or the NCJ.  But, I've never seen this.
If someone has the reference, I'd like to look it up since I get
questions about homebrewing the W3NQN filters with some frequency.

I built the W3NQN filters from scratch.  It's a bit of work.  But, it
can be done for about $40/band.  (Mine were cheaper because I got the
toroids as engineering samples.  Being a grad student does pay-off at
select times.)  I used inexpensive high-voltage capacitors from
Digi-Key.  These aren't rated for RF service; but, they seem to work
OK.  I really do need to go back and evaluate this choice at some
point.  The toroids, except for the T130-0, are available from W8DIZ.

You really need to have access to good measurement equipment to do it
right.  I built several of them without measuring anything and they
came out a little better than the Dunestars.  You can really tweak
them in, though, if you have a network analyzer or even just a regular
antenna analyzer or generator and a peak detector.


--Ethan, K8GU/9.
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