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Re: Helix vs. loopers



You loose 3 dB linear to circular, circular to circular of the same rotation 
is best for satellite work eliminating fading during rotational shift and 
multipath.
I agree about diminishing returns on a Helix. I have phased two for linear 
polorization ( counter rotating 1.2 GHz). The BBQ grill is a simple 
solution, 18 dBi 1.2 and 24 dBi 2.4 with a small form factor, I use it 
portable and it fits in my car. If you have room for a 12' boom why not a 
10' TVRO dish? You could go portable with a Semi Truck!

Art
----- Original Message ----- 
From: <w7lrd@comcast.net>
To: "Steve Raas" <sraas@optonline.net>; <amsat-bb@amsat.org>
Sent: Monday, May 07, 2007 9:13 PM
Subject: [amsat-bb] Re: Helix vs. loopers


> Steve and all
> I believe simply lengthing a helix will reach a point of diminishing 
> returns.  It would be better to stack a couple or even four twenty or so 
> turn turn helix antennas (from VE3NPC).  You could  with proper phasing 
> generate a CP signal from a couple of loopers.  I just haven't heard of 
> anyone doing that, though it looks good on paper.
> 73 Bob W7LRD
> Seattle
>
> -------------- Original message -------------- 
> From: Steve Raas <sraas@optonline.net>
>
>> In reading much of the discussion that has hit the BB lately in regards 
>> to
>> antennas I figured Ide toss in my questions to the group.
>>
>>
>>
>> In trying to figure out which style antenna is going to suit my needs 
>> best I
>> have a few questions.
>>
>>
>>
>> #1 Is a linear polarized antenna less efficient than a RHCP antenna when
>> trying to receive or transmit to a rhcp signal / receiver?
>>
>>
>>
>> #2 If yes.. in theory how much?
>>
>>
>>
>> #3 In looking @ pre-built helix options for 1.2g I have found the 
>> DSH23-12
>> which is a 23 cm RHCP 12 turn helix 14.5 dBic gain in a machined radome 
>> for
>> best weather protection. 1.2-1.3 GHz bandwidth. 50 ohm feed wit h N (f)
>> connector on 8" backplane. All stainless hardware; Designed for PHASE 3D
>> uplink operation. Wide bandwidth actually covers from 900 - 1600 MHz (
>> copied verbatium from the www.directivesystems.com website. In looking at
>> the specs of this helix, it seems it may not have the desired gain for 
>> P3E
>> or others. In 'theroy' is it possible to make a 24 turn helix , and if so
>> would I be correct in thinking that double the turns would provide at or
>> near 3.0 db of additional gain?
>>
>>
>>
>> #4 If yes to question 3 would this antenna be @ or near double the 
>> physical
>> length?
>>
>>
>>
>>
>>
>> In a email I sent to Dave @ Directive he told me that the loopers he has 
>> can
>> be arranged for vert/linear or horizontal polarization, so I do think 
>> that a
>> looper although a great antenna may not be the best single antenna 
>> solution
>> for 1.2 Uplin k.
>>
>>
>>
>> Thoughts, Ideas & comments please.
>>
>>
>>
>>
>>
>> -Steve Raas
>>
>> N2JDQ
>>
>> FN20vg
>>
>> _______________________________________________
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> _______________________________________________
> Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
> 


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