On Feb 13, 1:00*pm, wrote:
I have a Rohn 30 foot telescoping mast that I'd like to use as the
vertical element of a 40 meter ground plane. My idea is to add 3 feet
of pipe to the top of it to make it the required 33 ft. long.
I want to elevate the bottom of it about 8 feet of the ground and run
a couple of quarter wave wire radials out from it. This way they can
be walked under.
*My questions are these...
The ground slopes upward in one direction that I need to run a radial.
The radial will have to have an upward sweep in order to maintain the
clearance needed to walk under it. Will this be an issue?

The mast will be attached to my house to help support it. I can
insulate it from the mounting bracket with no problem. What I'm
wondering is with the fact of the mast being right up against the
house and not in the clear, how much will the performance of the
antenna be affected?

I have come up with this idea of a groundplane because I don't want to
deal with burying a whole bunch of radials in the ground. Think it
will work?
Tnx for any advice and suggestions and 73,
Michael, W4HIJ

I don't see how you will be able to elevate the base of that
fairly heavy mast to 8 feet, and still be able to raise and
lower it.
And.. it will need guy wires to keep from falling over.
Myself, I would use the 30 ft mast as the support and
build a lightweight aluminum radiator.
I made one from a junk 5/8 wave CB antenna.
The base was already fairly heavy duty, and I added
internal tubing to make the lower part stronger, and
adding progressively thinner tubing to get it to 32-33 ft.
The very top of the whip was a thin automotive whip.
The antenna itself is totally self supporting, and is
much easier to deal with than a heavy mast.
One person can hold it upright very easily.
But it would also let you have the base of the antenna
at 30 ft instead of 8, which would greatly reduce ground
loss vs the lower antenna.
Eight feet off the ground is not high enough on 40m to
greatly reduce the amount of radials needed vs a
ground mount. That's only 1/16 of a wave off the
ground.
With only two radials at 8 ft off the ground, your
ground losses are still going to be nearly as high
as if the antenna was on the ground.
But at 30 ft, which is almost a quarter wave up,
two radials would give you fairly decent performance.
I ran mine at 36 ft off the ground with four radials.
Was about equal to a ground mount with 60 radials
or so. Overall, the antenna kicked butt for DX
vs dipoles at 36 ft.
If you use two radials at eight feet up, I'm guessing
that would be appx equal to a ground mount with
4 radials or so.. Won't be a barn burner by any means..
It will "work".. But it won't be near as good as the
one I ran, unless you greatly increase the number
of radials for that low height above ground, or
get it higher up. With the telescoping mast, I was
able to try it at lower heights with the same four
radials. It was not near as good at say 16 ft up as it
was at 36 ft. Not even close really..