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Re: Metal vs. Fiberglass Boom



It's not quite as simple as portrayed.

You CAN use a metal boom, but the manner of mounting and placement of the
antennas is somewhat critical. There was a raging discussion about this very
topic with empirical data presented some time ago on the sig. Search the
archives.

To simply say " the purests say" or reduce it to the following:

>Mount crossed yagis so
> that they are not in the same plane as the cross-boom; X style rather than
> + style

is not a faithful characterizations of the care that needs to be taken when
using a metal boom with our satellite antennas. One really needs to read the
article and follow its directions carefully. One person who has is Roy
Welch, who frequents the mailing list, perhaps Roy can point to the
downloadable source.

In most cases (purists or not), if care is not taken about placement and not
just X versus + mounting, the circularity will be degraded. (not to mention
gain and f/b) The subject is much more complicated than Richard appears to
represent and I would urge that anyone contemplating using a conductive
boom, read the empirical work done by a satellite enthusiast with decent
test equipment and follow closely his recommendations.

Will it work "well" with a metal boom? Yes, if you follow the article. Would
I recommend it? No. Not if you can find fiberglas easily (which I had no
trouble doing).

73
hasan schiers, N0AN

schiers@netins.net
or use amsat.org or arrl.net remailer
----- Original Message -----
From: "Richard W L Limebear" <Richard@g3rwl.demon.co.uk>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, June 26, 2002 1:50 AM
Subject: Re: [amsat-bb] Metal vs. Fiberglass Boom


> "Tom & Judie Webb" writes:
>
> > but is a nonconductive
> > (fiberglass or PVC) REALLY necessary verses a metalic crossboom?
>
> NO.
>
> Purists say it will upset the antenna pattern. Sure, it will, to some
extent,
> but there is one measure you can take to lessen this. Mount crossed yagis
so
> that they are not in the same plane as the cross-boom; X style rather than
> + style. My yagis are all mounted in the centre of their booms too, rather
> than all forward of the cross-boom and getting balance problems.
>
> My system does this; it works ok. Even heard one of the Mars probes out
> beyond the moon with it. I might lose a dB or so but there are other
> things we can't change too (foliage, neighbors with shotguns, etc).
>
> This is *amateur* radio; do the best you can and you'll be surprised at
how
> well stuff works usually.
>
> 73
> Richard W L Limebear G3RWL
> g3rwl@amsat.org
> FOC # 1188
>
>           So many beautiful girls ..... (sob) so little time
> ----
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