Is this a multiband antenna? If so, I'd worry about the wire coupling
different parts of the antenna to each other differently and requiring
retuning at best, making it impossible to get a match at worst.

If it's a single band vertical, or at least just a single pipe without
traps then inside is the best bet. What you probably want to do is put
an RF choke both at the top and bottom.

Actually, I would suggest NOT putting the sensor at the top of a
vertical, but rather put it a few feet from the top. The tip of the
antenna is a high voltage point, and the top choke will be much more
effective if it's at a lower voltage point where some current is
flowing.

Run the wires up inside, use twisted pair, put a hole in the side of
the antenna at a few feet from the top and attach an insulating rod
sticking out sideways from that point. Put a good choke on the wires
where they exit the antenna element both at the hole near the top and
at the bottom of the element.

If it's a trapped vertical or something you'll have to worry about the
extra coupling between antenna segments due to the wire.

If you're only running 10 watts (I think you said), I doubt you'll have
to worry too much about arcing and so forth in the trapped situation,
but it will probably detune the antenna quite a bit even if you run it
inside.

73,
Dan
N3OX

On 2006-05-19, wrote:

Actually, I would suggest NOT putting the sensor at the top of a
vertical, but rather put it a few feet from the top.

Actually, for temperature, that might be the best idea yet. I could
run the wires entirely inside, stop somewhere away from the top, and
even disconnect the sensor with a PTT-triggered relay. The application
is a beacon, so the transmit will be very intermittant anyway. I'd
like to keep the entire antenna enclosed in PVC, with nothing hanging
on the side, which is what got me thinking about INside.

Thanks for all the replies.

--
Ben Jackson

http://www.ben.com/