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