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Re: RE: DIelectric Loading of Helical Antennas REPLY



Gunther (and all):
That's an interesting conclusion.  I have a couple of IEEE symposium papers where tape-wound helices were explicitly tested to see if they worked like wirewound ones; the conclusion was there was nearly zero difference.  The tests wound the tape both longitudinally and edgewise--both worked.

Besides, the Q of a conductor is more a function of its surface area; so even a thin tape should work ok as long as it's wide enough (you don't say how wide your tape was).  The usual electrostatic equivalence is tape width=2x wire diameter.

I wonder if the PVC had more of an effect than suspected...I have always wound my (short feed) helices on PVC, and to be honest believe their performance to be well below par; but haven't had time to experiment much with what adjustments (if any) would be applicable to the PVC core.

> 
> From: "Gunther Meisse" <gjmouse@neo.rr.com>
> Date: 2002/08/01 Thu PM 02:17:16 EDT
> To: <amsat-bb@AMSAT.Org>
> Subject: RE: [amsat-bb] 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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