[K3PZN-List] Again with my ignorance...

[n3mcb at bellsouth.net]

The post is not energized (or rather should not be). The stub feed point (the part that makes it a J) is a basically a balun (which is a form of RF-Choke or transformer). The idea being that all the metal below the feed point is made to disappear from the standpoint of the RF coming off the wire, just like a balun on a dipole causes the feed line shield to disappear and not radiate. This is the same reason why we don't care about the length of the mounting pipe or the length of a feed line when determining the resonance of an antenna.

Hope that helps,

WO3L Andy 
> 
> From: Curt Milton <wb8yyy at yahoo.com>
> Date: 2006/11/15 Wed PM 12:33:21 EST
> To: Carroll County Amateur Radio Club <k3pzn-list at mailman.qth.net>
> Subject: Re: [K3PZN-List] Again with my ignorance...
> 
> Bill
> 
> Good question.  
> 
> Is your metal post PAINTED or otherwise treated?  if
> so, this MAY be a factor.  
> 
> I suggest using your ohm-meter to see if there is
> apparent DC conductive contact between your antenna
> and the post.  (and try same from two different places
> on the post itself).  
> 
> If there is not conductive contact, then there is the
> possibility of capacitive contact (with the presence
> of paint acting like a dielectric).  
> 
> The other factor that could be involved is the level
> of the RF field at the point that the antenna makes
> contact with the post.  If this happened to be a null
> at both 144 and 440 MHz, well not much RF would get
> onto the post.  
> 
> Proceed with care and interest!  
> 
> Curt
> amateur with plenty of ignorance left
> 
> 
> --- "Neeriemer, Bill (NIH/NLM/LHC) [C]"
> <bneeriemer at mail.nih.gov> wrote:
> 
> > OK,  I've got a dual band j-pole made out of solid
> > aluminum pieces,
> > except for a couple of plastic pieces one the ends
> > to protect from
> > poking one's eye out.  (Actually I have 2, the other
> > is Stainless
> > Steel.)
> > 
> > I mounted it on a metal post approx 6' long.  (Steel
> > I think)
> > 
> > The mounting brackets are metal.  (probably
> > aluminum)
> > 
> > The system works well.  SWR = 1:1 consistently.  I
> > can be heard from
> > Westminster without difficulty.  I'm in Mt. Airy.
> > 
> > My question is:
> > 
> > What, if anything, prevents the entire contraption
> > including the post
> > from being energized when I transmit?
> > 
> > I'm not brave enough to touch the post to see if it
> > is energized.  I
> > decided to err on the side of caution and assume
> > that it is.
> > 
> > I see no evidence of any insulators anywhere on the
> > antenna or mounting
> > brackets.
> > 
> > It would seem to me that if the post is in fact
> > energized, then it would
> > be impossible to factory tune it.
> > 
> > Can someone explain this to me?
> > 
> > Thanks
> > 
> > 73 Bill W3STG
> > 
> >  
> > 
> >
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> 
> 
>  
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