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Re: mounting crossed yagis



Hi James,

Adding to other posters' notes, you may be interested to know that there's
one other thing which is strangely easier to do with X as opposed to +, and
that's to provide remote switching not only in RHCP and LHCP, but also in
horizontal and vertical linear polarization. This is described in the RSGB
Communications Handbook 7th edition, and also I describe a practical view on
http://www.btinternet.com/~hlong/remotepolarization.htm.

The ARRL Satellite Handbook also seems to suggest that using a pair of X
yagis phased in this way for linear polarization potentially gives you an
extra 3dB, so a 5x5 _could_ have the same gain as a 10 ele. I remain to be
convinced, and perhaps I've misunderstood! Perhaps an expert can comment.

I've used this scheme in the past and it's worked. I've found recently
however that in practice the crossed yagis seem to need to be designed to be
driven together to make this (or any other switched phasing scheme) work.
Crossed yagis which simply have two linear yagis placed at right angles on
the same conductive boom seem to couple quite badly in my experience making
tuning with switched phasing impossible, although with fixed phasing it's
possible with some patient adjustment.

73 Howard G6LVB

----- Original Message -----
From: James Farley <j.r.farley@ieee.org>
To: <amsat-bb@AMSAT.Org>
Sent: Monday, August 07, 2000 12:36 AM
Subject: [amsat-bb] mounting crossed yagis


> Hi all,
>
> I have built a pair of homebrew Yagi's to get onto the sats.  I was
> planning to mount them in the "+" configuration (one beam horizontal, one
> beam vertical) but recently saw an installation where the guy had put them
> in an "X" configuration.
>
> I was wondering if anyone has any thoughts on the advantages and
> disadvantages of each of these two configurations - the "+" would be
easier
> for me to mount, but if the "X" is much better it could be worth doing a
> bit more engineering to get it to work.
>
> Thanks in advance
>
> 73 de James VK2UJF
> Sydney, Australia
>
> ----
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