"Thomas C. Sefranek" wrote in message ...
"Dr. Slick" wrote in message
om...
Hi,

I built a Super J-Pole like this one:

http://www.nemr.net/~aschmitz/antennas/jpolecalc.html

For 300 watts, VHF frequencies. With i believe 6 turns of 4"
diameter
inductive loops in the coax (RG-213), just at the base of the antenna.

Problem was, the antenna had an intermittant problem, which turned
out
to be the dielectric foam material MELTING right at the inductive
loops in
the coax. I tore off the outer jacket, and the foam was melting and
oozing
past the outer braid, really nasty...so that the inner conductor was
intermittantly touching the outer braid, most likely.

A real hair-puller, because the super-J looked fine when i took it
down.

Can i get away without using the inductive loops? They are
supposed to be there to prevent the current from going down the
outside braid, right? So
that you don't have radiation along the coax?

Or perhaps i can make fewer turns, or larger diameter loops? So
that the
impedance discontinuity is less severe at this point?

Knowledgable advice much appreciated.


Slick

Why do you have this choke at the feed point?

ASS-U-ME the feed is correctly adjusted for a perfect match to the feedline,
what is to be gained by choking the feed line?

SWR and common modes currents are unrelated. You can have a perfect
match, and still have excess current on the coax shield. The gain? No
skewing of the pattern up off the horizon. MK

SWR and common modes currents are unrelated. You can have a perfect
match, and still have excess current on the coax shield.

Hi Mark, I agree, but those common mode currents can make your swr meter read
strange things.
If one has excess common mode current, the placement of ones swr meter along
the antenna system will effect what it reads. ok ok TLI meter.:-)
73 Gary N4AST