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RE: DIelectric Loading of Helical Antennas REPLY



Peter,
Just for what is worth. I built a 30 turn helix on PCV with 3m copper tape
and had very poor results. See my web page: www.wmfd.com/w8gsm  I think that
the problem is the thickness of the tape. It is a known fact that the dia of
the radiating source effects the bandwidth of the antenna. I am afraid that
the very thin tape (1 mil) just does not radiate in the forward direction as
you would hope. The field test I did on mine resulted in a swr of about
1.05:1, however the radiation was all in the side lobes.... I also built a
dual helix feed for my portable which you will see on the site. It also was
worthless. I went to the store and came back with # 10 wire and gently
soldered it over the tape and solved the problem. It now works great.
Keep me posted if do the project. I would love to hear how you do.
73
Gunther Meisse
W8GSM


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Pieter Ibelings
Sent: Thursday, August 01, 2002 10:40 AM
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] DIelectric Loading of Helical Antennas


Has anyone tried dielectrically loading a helical feed antenna. I have an
application where I would like to reduce the 2.4 GHz helical feed in my
portable setup to about half the size. I was thinking of using a fiberglass
tube to wind the copper tape helix on. I would then use the next fiberglass
tube in size to cover the outside of the helix. This way the helix would
have fiberglass on the inside and outside. Does anyone know if I can just
reduce all of the dimensions by the squareroot of (Er)? Any ideas?

Pieter N4IP


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