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Re: AOP-1 Circular Polarization?



----- 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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