[TowerTalk] Quadrifilar antenna

[Chris & Bill Shell]

Ford,
I use quadrifilar helix antennas for UHF uplinks.  The antennas provide a
fairly uniform hemispherical CP coverage pattern.  The pattern isn't truly
hemispherical since the pattern covers to about 5-10 degree depression from
the bottom plane.  The quadrifilar helix can be made to be very broad-banded
by increasing the size of the tubing used.  If you use 1 inch copper flex
water pipe you can achieve low VSWR from 400-450 MHz.
73, Bill
N6WS

-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Ford Peterson
Sent: Sunday, June 10, 2001 10:29 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Quadrifilar antenna


I have been reading Walt Maxwell's new book Reflections II.  He describes a
"Quadrifilar Helix" antenna used for satellite work.  Anybody played with
these babies?  I've been modeling the design and it looks quite promising.

180 degree az pattern over almost 175 degrees of elevation.   Wow!  It's a
cloud burner but just the ticket for LEO (Low Earth Orbit) satellite work.
I've been looking at making one but the materials are a problem.  There was
an article in QST a while back that described making one but frankly, the
cheesy construction leaves a bit to be desired.  In addition, there are
several aspects of the Maxwell paper that lead one to believe that the QST
version is a hoax (it can't possibly work at the top of a tower).

If somebody has experience with these antennas, I'd love to hear from them
direct.  Perhaps we can share notes, models, etc.

Ford-N0FP
ford@cmgate.com




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List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A HREF="http://www.ChampionRadio.com">
www.ChampionRadio.com</A>

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