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Re: 1/4"3m ribbon helix reply to replies



Hi,

My 5-1/4 turn helix (on my 33-inch offset-feed AO-40 dish) is wound around
1-inch I.D. gray PVC tubing with no discernable effect.  The No. 8 solid
copper wire is stiff enough that the coils do not actually contact the PVC,
though (it just gives them support if they bump up against something), so
maybe there is less dielectric effect on my helix (?).  Yes dielectric
propagation speed will likely effect tuning some what, but the helix is
such a low-Q, wideband antenna it seems it wouldn't be very significant.  I
do not have test equipment for 2.4G to determine this.

I am using a 3-1/4 turn helix feed on my 8-foot dish that used a small
3/8-inch plywood card form for the coil.  I should someday test it as I
have Bird power meter elements for 1.1-1.8 GHz.

Ed

At 10:14 PM 8/1/2002 -0400, 3.1415926535897932384626433832795028 wrote:
>I forgot to add that it is possible that the PVC is detuning the antenna and
>causing it to not perform. Even if the PVC is low loss, it will still have a
>loading effect that can mistune the antenna. The matching circuit would
>still be able to tune to a good return loss but the afficiency would be
>poor. This does not explain why  tape on PVC does not work while 10 AWG on
>PVC does.
>
>Pieter
>
>
>----- Original Message -----
>From: "Gunther Meisse" <gjmouse@neo.rr.com>
>To: <amsat-bb@AMSAT.Org>
>Sent: Thursday, August 01, 2002 9:43 PM
>Subject: [amsat-bb] 1/4"3m ribbon helix reply to replies
>
>
>> Gentlemen:
>> Well, for every action there is an equal and opposite reaction!!!!
>> I mustered some descent on that -bb posting..
>> I have loved the 3m copper ribbon helix concept, but have had bad luck
>with
>> them.
>> On the PVC, I gave the PVC the microwave Oven test and it passed well, but
>> the result stunk.
>> On the portable, I take note of the fact that my dual helix went from bad
>to
>> great with addition of the #10 wire suppered on the 1/4" tape.
>> The comment that the surface area is what counts interests me. In the case
>> of the 1/4" 3m tape, that is 1 mil thick, the "area" that faces the wave
>> front is only 1mil thick. Am I to understand that the "diameter of the
>> radiating conductor" is only important in terms of the total surface area,
>> or the surface area facing the wave front direction?
>> I noted with interest the wonderful pictures of foil helixes that I assume
>> work well.
>> When I get some time, I must start over and see if I can come up with some
>> better results. For the time being, for me, it is #10 or larger wire.
>> 73
>> Gunther Meisse
>> W8GSM
>>
>> ----
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>>
>----
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> 

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