[amsat-bb] Re: Cross Boom

[Joe]

No,
That will not make any difference.

we are ONLY thinking of the metal in the near field of the antenna,, and 
how it effects the radiation pattern as well as impedance of the antenna.

Now add in feedline radiation and you just oopened up a whole new can of 
worms.

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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>>
>>
>
>
>