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Re: PVC and J-pole Lessons relearned!



One of the best messages you have EVER sent to the BBS!  Cliff K7RR

Bob Bruninga wrote:
> 
> Argh.  Finished tuning up a nice dual band J-pole antenna
> and shoved it up inside its PVC housing.  Yuk.  I knew I
> would have to re-tweak it for the change in dialectric
> but I never thought it was 10 to 12%!
> 
> Basically had to completely rebuild the antenna and re-cut
> everything.  Resonance in air at 146 MHz dropped to 132 MHz
> inside the PVC.   So the right way is to not even waste time
> in air.  Just slide it into the PVC for every step in the
> tweaking process.
> 
> Also in looking at J-pole designs i found on the internet,
> I was amazed that everyone of them was fed what I think
> is wrong.  They hooked the shield of the coax to the
> stub and center to the radiator.  Sure that works, but it
> is very vulerable to even the slightest change in how
> the coax hangs.
> 
> Its better to take advantage of the inherent grounded nature
> of the vertical and run the coax alongside the main pole
> and keep it geometrically close to that grounded part of
> the antenna, then run the center conductor over to the "J".
> 
> This is far less vulnerable to how the coax hangs..
> 
> Just relearning old lessons...
> For what it's worth...
> de WB4APR, Bob
> 
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