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Re: R: Metal vs. Fiberglass Boom



The X configuration is required to keep the SWR low.  If you put it in a +
configuration, the SWR will go up.

i8cvs wrote:
> 
> Hi Joe K0VTY,
> 
> A crossed yagi antenna connected for circular polarization
> has two components at 90 deg out of phase wich resultant is
> a vector that rotates in the space 2 x 3,14 x f  every second
> or 360 degrees x frequency in Hz  every second.
> 
> Now if you have  the 2 meter antenna in + configuration and
> the 70 cm antenna in X configuration or both in X configuration
> or both in + cofiguration the isolation between the antennas is
> the same because the above 2 meters and 70 cm vectors rotates.
> like a two bladed propeller.
> 
> The same is true if you use a metal boom,no matter if you put the
> elements in X configuration or + configuration because in any
> case the EM rotating vector of circular polarizazion sees the metallic
> boom or better is obscurated by it,or cross it one time for every
> cycle of the exiciting frequency.
> 
> To demostrate that X is better than + configuration is necessary
> to demostrate first for what physical law the resultant EM rotating
> vector on X configuration should not see the metallic boom crossing
>  it every cycle of the exciting frequency.
> 
> 73" de i8CVS Domenico
> 
> 
> ----- Original Message -----
> From: joseph Murray <k0vty@juno.com>
> To: <schiers@netins.net>; <amsat-bb@AMSAT.Org>
> Sent: Wednesday, June 26, 2002 2:32 PM
> Subject: Re: [amsat-bb] 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
> > > > ----
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> > >
> > >
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> >
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-- 
73, Roy -- W0SL

E-Mail: rdwelch@swbell.net
Home Page: http://home.swbell.net/rdwelch
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