[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Metal vs. Fiberglass Boom



Hi All

I'll add one more tidbit on cross booms that I had to learn.
My desire to use mode J ( 145 up and 435 down ) and the receiver de sense
problem had me scratching my head.     Antenna isolation can improved the
de sense problem.   Aligning the 2 meter antenna elements in a X
configuration and the 70 cm elements in a + increases the isolation .  
Unless you are using the non metal cross boom this is difficult to do
when using circularly polarized antennas.

Joe  K0VTY
========================
On Wed, 26 Jun 2002 06:33:17 -0500 "hasan schiers" <schiers@netins.net>
writes:
> 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
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to 
> Majordomo@amsat.org
> 
> 
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 

________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
http://dl.www.juno.com/get/web/.
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home