[amsat-bb] Re: AOP-1 Circular Polarization?
w4as at bellsouth.net
Mon May 19 07:15:14 PDT 2008
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 at hotmail.com>
> To: "Ronald G. Parsons" <w5rkn at amsat.org>; <amsat-bb at 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
>> 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.
>> satellite work, with accurate keps, this is probably not a
>> issue, but for terrestrial work and other situations where the
>> 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
> 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
> 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
> 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
> 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
> the X or + configuration can be used indifferently if you use an
> boom like fiberglass or wooden boom as demonstrated with experiments
> by WA5VJB
> In addition the X configuration is nice if you want to add V and H
> 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 at amsat.org
>>> To: amsat-bb at 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
>>> radiation wise, it doesn't matter whether you mount them in an X
>>> or +
>>> orientation. The only difference would be the phase of the
>>> you are not concerned with that. There could also be a difference
>>> right- or left-circular polarization, but whether that matters
>>> the polarization the the satellite's antenna. But X or + does not
>>> 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
>>>> Content-Type: text/plain; charset=US-ASCII; format=flowed;
>>>> Hello all, I'm getting ready to put back up my old AOP-1 antennas
>>>> old Cushcraft antennas that were popular in the days of AO-10 &
>>>> 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.
>>>> 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
>>>> today's birds.
>>>> 73s de W4AS
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