[amsat-bb] Re: Cross Boom

23 Apr 2009

      It's here on Howard's site:
http://www.g6lvb.com/fibermetalboom.htm
--- On Wed, 4/22/09, Edward Cole kl7uw@acsalaska.net wrote:
...
From: Edward Cole kl7uw@acsalaska.net
Subject: Re: [amsat-bb] Re: Cross Boom
To: "Jeff Yanko" wb3jfs@cox.net, kq6ea@pacbell.net, "Joe" nss@mwt.net, "Billy Simpkins" bsimpkins31@dishmail.net
Cc: amsat-bb@amsat.org
Date: Wednesday, April 22, 2009, 10:39 PM
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@pacbell.net
...
To: "Joe" nss@mwt.net; "Billy
Simpkins" bsimpkins31@dishmail.net; "Jeff
...
Yanko" wb3jfs@cox.net
Cc: amsat-bb@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@cox.net wrote:
...
...
...
From: Jeff Yanko wb3jfs@cox.net
Subject: [amsat-bb] Re: Cross Boom
To: "Joe" nss@mwt.net,
"Billy Simpkins" bsimpkins31@dishmail.net
...
...
...
Cc: amsat-bb@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@mwt.net
To: "Billy Simpkins"
bsimpkins31@dishmail.net
Cc: amsat-bb@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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