[amsat-bb] Re: Cross Boom

[Edward Cole]

The coax shield coming off the antenna boom at a right angle looks 
like another parasitic element being added to the antenna causing 
severe distortion of the antenna pattern.  But if one installs the 
antenna in the X configuration and attach the cross boom in a 
location away from any of the elements one can tightly run the coax 
across the metallic cross boom with little effect.  This was tested 
by WA5VJB and is a published article.

I have my M2 436CP42UG mounted in this fashion and it preforms well.

73, Ed - KL7UW
maybe someone else can point to the link to that article.

At 11:41 AM 4/22/2009, Jeff Yanko wrote:
>OK, I see where this is coming into play.  So it's possible that the coax
>shield could react to the feedpoint system and pattern.  Now this raises a
>question.  If this is the case, has anybody tried a broadband choke balun to
>limit this potential problem?  If you think about it, the bigger issue with
>coax effecting the radiation pattern is improper decoupling of the fed
>point.  If the outside shield is hot with RF it will radiated and effect the
>pattern big time. If the coax is properly decoupled at the fed point the
>outside shield will ideally have zero rf current on it and ideally have no
>impact on the pattern.
>
>Thoughts?
>
>
>73,
>
>Jeff  WB3JFS
>
>
>----- Original Message -----
>From: "Jim Jerzycke" <kq6ea at pacbell.net>
>To: "Joe" <nss at mwt.net>; "Billy Simpkins" <bsimpkins31 at dishmail.net>; "Jeff
>Yanko" <wb3jfs at cox.net>
>Cc: <amsat-bb at amsat.org>
>Sent: Wednesday, April 22, 2009 11:09 AM
>Subject: Re: [amsat-bb] Re: Cross Boom
>
>
> >
> > Because the shield of the coax "looks" like a piece of pipe, and has the
> > same effect on the antenna pattern that you're trying to eliminate by
> > going to a non-metallic cross-boom.
> > Jim  KQ6EA
> >
> >
> > --- On Wed, 4/22/09, Jeff Yanko <wb3jfs at cox.net> wrote:
> >
> >> From: Jeff Yanko <wb3jfs at cox.net>
> >> Subject: [amsat-bb] Re: Cross Boom
> >> To: "Joe" <nss at mwt.net>, "Billy Simpkins" <bsimpkins31 at dishmail.net>
> >> Cc: amsat-bb at amsat.org
> >> Date: Wednesday, April 22, 2009, 10:55 AM
> >> Hi all,
> >>  I found this line confusing....
> >>
> >> "But then  if you go insulated  then do not run the
> >> feedline along it either
> >> or you just defeated the purpose of the insulated
> >> boom."
> >>
> >> My question is if you run the coax along an insulated
> >> crossboom, ie.
> >> fiberglass, how could that affect the coupling of the
> >> transmission line when
> >> the object it is being attached to is
> >> "insulated"?
> >>
> >>
> >> 73,
> >>
> >> Jeff  WB3JFS
> >>
> >>
> >>
> >>
> >>
> >> ----- Original Message -----
> >> From: "Joe" <nss at mwt.net>
> >> To: "Billy Simpkins"
> >> <bsimpkins31 at dishmail.net>
> >> Cc: <amsat-bb at amsat.org>
> >> Sent: Wednesday, April 22, 2009 7:06 AM
> >> Subject: [amsat-bb] Re: Cross Boom
> >>
> >>
> >> > It all depends on how the elements are mounted.
> >> >
> >> > If at 45 to 90 degrees from the crossarm,  no propblem
> >> and use anything,
> >> >
> >> > But if in the same plane  then need insulated
> >> crossboom,
> >> >
> >> > But then  if you go insulated  then do not run the
> >> feedline along it
> >> > either or you just defeated the purpose of the
> >> insulated boom.
> >> >
> >> > Billy Simpkins wrote:
> >> >
> >> >>Is a fiber glass or some other non-conductive
> >> material necessary for a
> >> >>cross boom?  What or the advantages and
> >> disadvantages versus a metal one?
> >> >>
> >> >>Thanks,
> >> >>Billy KF0CK
> >> >>_______________________________________________
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> >> >>
> >> >>
> >> >>
> >> > _______________________________________________
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> >>
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>
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