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PVC and J-pole Lessons relearned!



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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