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Old February 10th 06, 08:33 PM posted to rec.radio.amateur.antenna
kevin
 
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Default help appreciated with unusual j pole feed


hi there, i'm looking for some help with a j pole antenna, it's actually a
vhf marine antenna so i hope it will be ok to ask here.

my problem is that this antenna used be atop the mast of my yacht untill it
blew off breaking the end fitting and pulling free of the coax, because
these things are quite expensive and don't seem to last that long, I decided
to try repair it as a spare.

It fits inside a fibreglass tube, so I carefully cut through the tube and
pulled out the antenna parts, which are all intact.

my plan was to solder some coax to it and put it back in the tube, then
glass the tube back together, but this is where i ran into trouble, i'm
unsure where to afix the coax.

the antenna i believe is a j antenna, with a 3/4 wave leg and a somewhat
less than a 1/4 wave leg returning from the base, however there is no
connections on this stub part where the coax has been connected, i had
expected there would be.

There is, however, 2 pins below the 2 upright legs, these are not
electically connected to the upright stub elements, (the 2 upright elements
are joined across the bottom). These 2 pins have a length of insulated wire
attached to them which stretches over and parallel to the uprights of the
stub. The 2 pins are staggered in height which means 1 side of this
insulated wire run is approx 75 mm and the other side is approx 70 mm, it
runs like an inverted v up the stub from these pins at the base.

I'm assuming that the coax should also be soldered to these 2 pins and
interacts with the antenna through induction or something. If this is
correct does it matter which side of the coax goes to which pin, neither of
them are conneced to anything other than each other through the insulated
wire, which as i've said, runs above what i beleive to be the antenna stub
section.

or should the coax be connected at the top of the stub, ( a halfwave from
the top), i can't see any sign that the coax was previously fixed there, but
then there is no sign that it was previously connected anywhere for that
matter

hope this makes sense and someone is able advise, thanks for looking and if
you can help thanks again.

if this all sounds like nonesense, i may be able to put a picture as an
attachment but i'm unsure whether it is acceptable in this group.

kevin





 
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