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Re: AOP-1 Circular Polarization?



Thanks for everyone's replies.  It looks like the consensus is to  
mount the beams in the terrestrial + pattern (vertical/horizontal).   
I'll be mounting the antennas on a fiberglass pole that served me well  
years ago (it's been keep safe inside the attic).  This is good,  
because that way I should be able to use those antennas for local  
repeater work with minimal loss if any, due to using both polarities  
at the same time.

On May 19, 2008, at 4:44 AM, i8cvs wrote:

> ----- Original Message -----
> From: "Greg D." <ko6th_greg@hotmail.com>
> To: "Ronald G. Parsons" <w5rkn@amsat.org>; <amsat-bb@amsat.org>
> Sent: Monday, May 19, 2008 9:17 AM
> Subject: [amsat-bb] Re: AOP-1 Circular Polarization?
>>
>> Actually, I was thinking about this today...  There was an earlier  
>> thread
>> which discussed the off-angle performance of a crossed Yagi, and if I
>> recall, the pattern becomes elliptical as you move off the  
>> antenna's bore
>> sight.   If this is true, then I conclude that it would be better  
>> to mount
>> a crossed Yagi in the + orientation, vs X, as that way one of the two
>> antennas will be properly aligned for an off-angle linear station.   
>> For
>> satellite work, with accurate keps, this is probably not a  
>> significant
>> issue, but for terrestrial work and other situations where the  
>> target's
>> position may not be known or tracked, + should be more forgiving  
>> than X.
>> At least, that's my theory.
>>
>> I kind of hope I'm wrong on this...  I just got a new 70cm antenna  
>> from a
>> swap meet today, and it's already mounted in the X position.
>>
>> Greg  KO6TH
>>
>>
> Hi Greg, KO6TH
>
> The interferometer-like effect that you mentioned is referred only  
> to a dual
> boom antenna mounted configuration no matter if the antennas are  
> mounted
> in a X or + configuration.
>
> The distance between the two antennas make the phase of the received /
> transmitted signals to be different when the antennas are moved bore  
> sight
> from the satellite.
>
> Depending on the squint angle between the off-boom antennas and the
> satellite the above phase difference can make a RHCP signal to  
> appear LHCP
> or elliptical or linear.
>
> If  both antennas are mounted instead over a single concentric boom  
> this
> interferometer-like effect cancel out no matter if the antennas are  
> in a X
> or + configuration.
>
> This effect has been described into "The Satellite Experimenter's  
> Handbook"
> by  Martin Davidoff , K2UBC 2nd Edition pages 7-12 and 7-13
>
> By the way the X configuration is the best if you use a metal-boom  
> while
> the X or  + configuration can be used indifferently if you use an  
> insulated
> boom like fiberglass or wooden boom as demonstrated with experiments
> by WA5VJB
>
> http://www.g6lvb.com/fibermetalboom.htm
>
> In addition the X configuration is nice if you want to add V and H  
> linear
> polarizations using a relay switcher for V-H-RHCP-LHCP as described
> into the AMSAT Journal March/April 2007 and May/June 2007
>
> 73" de
>
> i8CVS Domenico
>
>> ----------------------------------------
>>> From: w5rkn@amsat.org
>>> To: amsat-bb@amsat.org
>>> Date: Sun, 18 May 2008 16:42:02 -0500
>>> Subject: [amsat-bb] Re: AOP-1 Circular Polarization?
>>>
>>> Assuming the antennas you reference do produce circular  
>>> polarization,
>>> radiation wise, it doesn't matter whether you mount them in an X  
>>> or +
>>> orientation. The only difference would be the phase of the  
>>> radiation,
> and
>>> you are not concerned with that. There could also be a difference
> between
>>> right- or left-circular polarization, but whether that matters  
>>> depends
> on
>>> the polarization the the satellite's antenna. But X or + does not  
>>> change
>>> that.
>>>
>>> There might be some mechanical reason for an X or +, such as weather
>>> proofing, but not signal wise.
>>>
>>> Ron W5RKN
>>>
>>>> Date: Sun, 18 May 2008 14:28:34 -0400
>>>> From: Sebastian
>>>> Subject: [amsat-bb]  AOP-1 Circular Polarization?
>>>> To: Amsat - BBs
>>>> Message-ID:
>>>> Content-Type: text/plain; charset=US-ASCII; format=flowed;  
>>>> delsp=yes
>>>>
>>>> Hello all, I'm getting ready to put back up my old AOP-1 antennas  
>>>> (the
>>>> old Cushcraft antennas that were popular in the days of AO-10 &  
>>>> 13).
>>>> I'm wondering whether I should follow the same procedure of cross
>>>> polarization for the 440 beam?  It was recommended at the time to
>>>> place the antenna in an X pattern instead of the cross pattern.   
>>>> Also,
>>>> at the time, the 2 meter antenna was suggested to be placed in the
>>>> standard vertical/horizontal polarization.
>>>>
>>>> Please let me know which would be the best method to use for most  
>>>> of
>>>> today's birds.
>>>>
>>>> 73s de W4AS
>>>>
>>>>
>
>
>
>
>
> _______________________________________________
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