wrote in message
...
Just wondering what people's opinion is on this... I'm trying to
decrease the overall mounted size of a jpole design. In the past I've
always tried to keep the bottom 1/4 wave stub section well above the
mast top. Just for the heck of it, I started testing with the stub
below the top of the mast (mast blocking the bottom 1/4 wave stub).
The antenna is still electrically isolated from the mast of course...
but what I found is that I was able to mount the antenna to the mast
and have it go up the first 1/4 wave stub part of the antenna at least
2/3 of the way, before there was any SWR problem at all. In fact,
there was virtually no difference in the SWR doing that, as compared
with having the very bottom of the antenna well above the mast top.
Can anybody think of any other adverse effect in doing this? On a
fairly low band it reduces the overall size of the antenna
significantly, so it's definitely an advantage to mount it lower,
assuming there's no adverse effect on the performance. The SWR doesn't
seem to change at all until you start getting the top of the mast up
near the actual 1/2 wave portion of the antenna.

That's interesting. My experience is related to yours, although what I did
was bring the mast close to the entire long part of the "J" and found I had
to get within an inch before I saw any measurable effects, rcv or xmit. I
did it with a 2m copper J.

In your situation, possibly the quarter-wave section is a tank circuit and
would need proximity of a mast section of size close to its resonant freq to
be detuned by it. I don't know ... just musing. Others will mug me for
getting it wrong and that's OK.

More musing: Does the entire "J" have to be upright? Can't I put an elbow
where the quarter-wave and half-wave sections meet, so the radiating element
is vertical, but the quarter-wave section is horizontal? (In the case of a
tower side-mount, this would position the radiating section a nice distance
from the tower. Inverted OK.)

"Sal"