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Re: RE: DIelectric Loading of Helical Antennas REPLY



One significant difference of Pieter's helices/tubes is that his tubes are
very thin and of a different material.
Pieter's are polyethelene, maybe .020" wall thickness.  "The rest" are
polyvinylchloride (PVC) and about 0.13-0.15" wall thickness.

At 20:23 2002-08-01 -0400, 3.1415926535897932384626433832795028 wrote:
>
>I have only used tape helix antennas for all of my AO-40 needs and they work
>really well. I have tried them from 3 turns all the way to 78+ turns and
>have always gotten good results when the number of turns is less than 20 or
>so. Last year when I went to the Air and Space museum I spotted a couple.
>One of the tape helix antennas was actually used on the Viking Probe S band
>antenna:
>
>http://ozoni.com/n4ip/viking.jpg
>
>Here are some pictures of my own tape helix antennas wound on thin plastic
>tubes:
>
>http://www.ozoni.com/n4ip
>
>I will give the fiberglass antenna a try to see how it performs.
>
>73's
>
>Pieter
>
>----- Original Message -----
>From: <nx7u@cox.net>
>To: <gjmouse@neo.rr.com>; <amsat-bb@amsat.org>
>Sent: Thursday, August 01, 2002 4:37 PM
>Subject: Re: RE: [amsat-bb] 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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>> >
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>>
>> ----
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>>
>
------------
Scott Townley		
nx7u@arrl.net
Gilbert, AZ  DM43
     
HF/VHF/UHF/Satellite MOBILE station
--> NEW ADDRESS  http://www.mindspring.com/~nx7u

------------
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