[amsat-bb] Re: Re crossed yagi question.
domenico.i8cvs at tin.it
Sat Jul 26 07:42:40 PDT 2008
----- Original Message -----
From: "Angus" <angus at young5769.freeserve.co.uk>
To: <amsat-bb at amsat.org>
Sent: Saturday, July 26, 2008 3:29 PM
Subject: [amsat-bb] Re crossed yagi question.
> OK now that I have a crossed yagi in the X format, I must say I am very
pleased with its performance.
> Here is the question with the yagi in the X format, does it perform as
well when set with delay lines to horizontal polarity as a yagi with the
same gain beam width etc set in the horizontal polarity?
> I ask this as I don't have a lot of test equipment and most of my results
are a 'by ear' equipment.
> I just wonder if anyone (someone will have I am sure) has done any
checking to see what if any difference there is between X set to Horizontal
and a normal yagi set in horizontal?
> Thanks for allowing me to ask what might be some very daft/odd questions
> Gus M0IKB
Hi Gus, M0IKB
If you want the switching polarization agility be happy with your crossed
yagi in the X format.
In theory your polarization switcher send 50% of power to the \ yagi and the
other 50 % to the other / yagi.
The components \ and / can be combined by the switcher to make a resultant
that can be horizontal or vertical but any polarization switcher has losses
due to relays and delay lines.
In particular to divide exactly the power 50% to the \ dipole and / dipole
is difficult and this can generate a resultant that is not exacly horizontal
or exactly vertical.
In conclusion if you feed 100% of your power to a single horizontal antenna
or to a single vertical one it is better but if you need the polarization
agility to get V-H-RHCP and LHCP there is no way to do different and a good
polarization switcher is mandatory.
For the theory on how a four polarity switch works read please the article
"Switching Four Polarizations on a 70 cm Crossed yagi" Part-1 publisched
in the AMSAT Journal March/April 2007 www.amsat.org
For building the switcher read Part-2 in the issue May/June 2007
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