Mounting on a metal crossboom is fine, as long as you avoid the couple of spots pointed out in the paper referenced below.
The manufacturers may have thought that too difficult to explain, or thought people would disregard the positioning. Maybe they had a deal with someone who made the fiberglass crossbooms. I do not know.
I do know a metal crossboom as described in Kent’s paper can work very well as was actually measured on an antenna range.
73,
Joe kk0sd
From: Calvin McDonald via AMSAT-BB <[email protected]>
Sent: Sunday, September 10, 2023 6:20 PM
To: AMSAT-BB <[email protected]>
Subject: [AMSAT-BB] Re: Cross Polarized Yagi: X or +
I was under the impression that it didn't matter how that antenna was oriented (it circular) and that a conductive mast shouldn't be used.
From the manual for the M2 circular polarized 70cm yagi:
“The 436CP30 is a circular polarized antenna and creates a field in all planes or polarities. Performance DETERIORATES SIGNIFICANTLY if it is mounted on a metal (conductive) mast or cross boom. A mast or cross boom of any NON-CONDUCTIVE
material must be used. Fiberglass is the prime choice for its strength and weather resistance. Mount the 436CP30 so that element tips are at least 12” from any conductive material (mast, tower, feed line, etc.).”
Cal - N7AY
On 9/10/2023 4:39 PM, Gary via AMSAT-BB wrote:
It will allow you to use a conductive crossboom, and/or route your feedline back out of the antennas along the crossboom. Antenna guru Kent Britain, wa5vjb studied and tested this.
He wrote a paper on it and published it as part of an AMSAT symposium. You can see the paper here:
Using Metal Cross Booms w/ Satellite Antennas (kk0sd.net)
73,
Joe kk0sd
I was advised by someone I think is knowledgeable, and certainly more so than me, to orient my cross polarized 2m Yagi so that the elements resemble an X rather than a +. Easily
enough done...what's the advantage?
It's my understanding that the two sets of elements are out of phase by 90° & combined at the common feed point to emulate circular polarization. How does the rotation along the
boom axis make a difference?
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