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

Yes Michael it will work fine. Keep the radials parallel to the ground
under them and they will be fine.
A suggestion - keep it at 30 feet for simplicity. Make sure it is insulated
where you attach to the house, the more the better.
Now the reason I say keep it at 30 feet is make it easier to build, because
you have an unknown (how much the house is going to detune things). So the
way you make up for this is with some matching at the base or with an
antenna tuner in the shack. Since it will probably be too short because of
the missing 3 feet, you will add some coil at the base which you make
variable until you get the swr to a reasonable level, say around 2:1. Then
just get on the air with it and make contacts. A 30 ft antenna works the
same as a 33 foot one.

Rick

On Fri, 13 Feb 2009 11:00:06 -0800 (PST),
wrote:

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?

Hi Michael,

No more than any other design - which is to say it will fit into the
solution without any more effort or problems.

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 would be more concerned with mechanical issues (like the moment arm
of the antenna ripping out a wall). Of course, this concern is rather
limited. As for the effect on performance - yes it will affect it. Do
you have any alternatives? If you do, those alternatives would
probably not bring any significant change (improvement or otherwise)
unless your home has metal siding (or metal mesh stucco). Wood is,
afterall, an insulator; and a house is largely filled with air,
another insulator.

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?

You are probably going to have to tune the antenna, or use a tuner.
Adding the "necessary" X feet to the top might do it, but simply plan
on building in a match or using a tuner and be done with it as a
problem. As for the radials, this is an issue of loss. If you can
put up with the loss, you don't need a "whole bunch." How much loss?
Probably less than the width of an S-Meter needle variation between
what you plan, and what you might do in a full scale elaboration.

73's
Richard Clark, KB7QHC

Thanks Guys for the answers. I'm hoping to tune the antenna with the
internal tuner on my radio. It's not a wide range tuner though so I
may have to work with some type of matching solution at the base. What
my reading on ground mounted quarter wave verticals makes me think is
that I'd want about 16 radials. That qualifies as a bunch to me...hi
hi... Easier in my mind to raise the base of the antenna 8 to 10 feet
off the ground and use a couple of elevated radials.
I think the mast will be ok structurally speaking mounted to the
house. It held up rotators and a small satellite array for years
without pulling the wall down. It will still be attached at ground
level with some type of non conductive support. The mounting bracket
won't be the only thing holding it, in other words.
What I'm after here with this project is better low angle radiation
for the purpose of working DX. My present 40 meter antenna is a dipole
that is only about 20 feet of the ground. Not ideal as I'm sure you
guys well know.

On Fri, 13 Feb 2009 16:46:29 -0800 (PST),
wrote:

What I'm after here with this project is better low angle radiation
for the purpose of working DX. My present 40 meter antenna is a dipole
that is only about 20 feet of the ground. Not ideal as I'm sure you
guys well know.

Hi Michael,

Your goal is admirable. Your goal shares the same aspiration of many
others who select a vertical antenna. We hear this goal quite often
as a reason for its choice. Unfortunately....

The greatest indicator of success in achieving low angle radiation for
a vertical antenna is actually found many wavelengths away from your
antenna - in the quality of the soil surrounding it at this distance.
The quality can be roughly determined by general descriptive
categories (like living next to a swamp or the ocean); or by reviewing
the FFC's ground charts.

Significant elevation of a vertical can reduce ground loss through
distance. It has been reported that the need for large numbers of
radials declines with this distance. You might think of hiking your
vertical higher. This reduction of loss translates into better
performance at lower angles, but it is not in its own right a solution
to better low angle performance as may be expected from simple
diagrams found in elementary discussion.

The best you can hope for is keeping both antennas, and trading from
one to the other for their diversity (when one won't work, the other
might). It serves no purpose to launch your RF off at 1 degree above
the horizon when it would only land in the Atlantic, skip a continent,
and land in the Indian Ocean. Propagation conditions will always
trump intention.

73's
Richard Clark, KB7QHC

On Fri, 13 Feb 2009 11:00:06 -0800 (PST),
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


As a kid, I had a 33-foot 40 meter groundplane of suplus aluminum
tubing, supported by the house and a few guy wires. There were 4 or 5
buried radials, and it worked nicely on 15 watts CW with the
pi-network output of a Heath AT-1 transmitter. I can't think of why
your proposed antenna shouldn't work. The main issue might be high rf
power playing havoc with your house electricals.

bob
k5qwg

wrote in news:2477b02a-bc76-4a0d-a04d-
:

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,

I modelled this the other night over a 15-degree slope

Basically, the pattern will have only about a 10db null. The pattern
will be good at low angles downslope and a bit raised upslope. The
antenna will even be half decent for NVIS at medium distance downslope.

In short, go for it!


--
Dave Oldridge+
ICQ 454777283
VA7CZ

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..

Suggestion.

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.

I've been using elevated quarter wavelength verticals in 4 square vertical
array operations for years like this. But there is a way to do this which is
FAR safer for you relative to lightning strike issues as well.

In my case, the vertical element is always a solid metal pole/tower which goes
all the way down to and into the ground at the base. This works even without
the elevated model with elevated radials as well.

Feed the vertical element at the feed point height, ground level, 8 feet up for
you - whatever, with a gamma match section attached directly to your coax feed
line. I make my gamma match sections with the little six inch TV feed line
holders through which I thread copper wire in the little brown insulators that
are out away from the pole by their length. You tie the feed point up at the
top of a run of several of these. Then at the bottom at the feed point for the
coax, you bond your coax braid to the actual tower element.

You run the hot tip wire for it to, at first, a variable capacitor which you
adjust for the desired flat SWR match for the feed. Of course if you are going
to use that variable permanently for the required capacitor in the gamma match
section, it will need to be decent enough spacing for whatever power level you
intend to use with the array.

But there is another trick! You can use a small receiving spaced variable
capacitor to do the experimentation for the match with one of these little
antenna analyzer units, Or .. even just and SWR meter in a crude sense. Then
when you get the nice perfect flat match with the variable, you can figure out
the capacitance needed for how many feet of your feed coax that would be!
Usually it is only a few feet or so on 40 meters for RG-8 for example. You cut
a piece of it that will have MORE than the required capacitance. You tie the
braid to your hot tip point feed wire from the feeder coax. You then tie the
tip point of the little piece of feed coax that is being used as a capacitor in
this case to your gamma match input wire tip.

At that point, you take a cutter, and start snipping off little bits of the
short coax piece you use for the capacitor! When the SWR comes down to the
intended bottom nicest value, you simply strip a little more of the braid off
the free end of the capacitor coax chunk, leaving the insulation and center
wire free in the air for an inch or so. And tape over it with tape to protect
the end from the weather if you like.

Presto! Absolutely flat SWR match to your vertical element that will stay out
there in the weather for years with no trouble. Since the mast is always hard
flat grounded to the earth, in concrete for my towers, or with a few little six
foot radials around the ground point for poles, to distribute the lightning
strike into the surface, POOF no lightning damage to the place!

Sure .. you bring the feed coax down to ground level. You go under the surface
to the shack, with a gas discharge protector plan on it as normal.

My 80 meter 4 square built like this .. four gamma match sections, one on each
element, gets hit directly at my QTH at least once a year here. Absolutely no
damage to the shack stuff from this ever for almost two decades of this now.
And it is connected and up 24X7 just like the broadcast tower stuff.

W5WQN

--


-- Sleep well; OS2's still awake!

Mike Luther

On Feb 19, 8:35*am, Mike Luther wrote:


My 80 meter 4 square built like this .. four gamma match sections, one on each
element, gets hit directly at my QTH at least once a year here. *Absolutely no
damage to the shack stuff from this ever for almost two decades of this now.
And it is connected and up 24X7 just like the broadcast tower stuff.

W5WQN

--

-- Sleep well; OS2's still awake!

Mike Luther

That's why all my antenna masts are metal and run all the
way down to the ground.
I don't know how many strikes I've had, but I know I've had
two of them with me sitting in this chair, which is about
15-20 feet away from the mast.
I've never had any damage. It's kind of weird..I don't
think I ever took a direct strike when I had the 40m GP
going. And it was nearly 70 ft up to the tip. Both strikes
that I saw were just hitting the 36 ft mast, which was
supporting wire dipoles at the time.