[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Helix vs. loopers



I have found that the support material has an effect on heilxes over 10T. A 
40 turn helix can be a challenge to support, and winding it on solid PVC 
pipe will have a considerable effect on the gain of long Helixes. Plastic 
charaterstics at microwave frequencies must be considered and if it slows 
the wave the helix will loose its focus.
Support rods help, but make for a flimsy antenna. Best to phase shorter ones 
for a robust antenna.

Art, KC6UQH
----- Original Message ----- 
From: "Clare Fowler" <lcfowler@magma.ca>
To: "amsat-bb" <amsat-bb@amsat.org>
Sent: Tuesday, May 08, 2007 5:52 PM
Subject: [amsat-bb] Re: Helix vs. loopers


> Helix antennas can be constructed to provide usefull gain with up to 40
> turns if designed with a circumference of one wavelength and a pitch angle
> of 12.5 degrees.
> In my direct experimental comparison measurements outlined
> in the May/June 2006 AMSAT Journal the max gain formulas used on
> various web sites and amateur publications, for as yet some undetermined
> reason, do not provide the predicted gain, but had less gain and increased
> side lobes. The longer the antenna the greater the deviation from that
> predicted.
>
> As stated previously feed line losses are a big problem for many hams
> at 1.2 GHz. My array (VE3NPC) is fed with 5 ft of RG/8U in the shack, 35
> feet of 1/2 in hard line and another 5 feet of flexible RG/8U at the
> antenna.
>
> I have 10 watts from my FT-736 and have never measured what it is at the
> antenna.  It perfomed very well on AO-40 where I logged 832 SSB QSO's in
> mode L/S.
>
> For helix design dimensions go to http://www.rac.ca
> and select calculators, helix antennas and then Kraus.
> (not Emerson as those max gain dimensions result in a
> poorly performing antenna).
>
> Clare VE3NPC
>
> ----- Original Message ----- 
> From: "kc6uqh" <kc6uqh@cox.net>
> To: <w7lrd@comcast.net>; "Steve Raas" <sraas@optonline.net>;
> <amsat-bb@amsat.org>
> Sent: Tuesday, May 08, 2007 12:46 AM
> Subject: [amsat-bb] 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
>
> _______________________________________________
> 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
> 


_______________________________________________
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



AMSAT Top AMSAT Home