I have never had a vertical without RFI problems.
Quarter wave, half wave, ground or in the air. Until now.
But......
My BiggIR Fluidmotion vertical is on a 4000 foot metal fence and is about
200 feet from the shack (I live in the country).
So I'm not surprised the alarms don't go off.
I'm about to mount it on the 3500 sq ft Al roof and ground it well.
We shall see,
As far as inexpensive and effective on 20, build a resonant dipole and mount
it however you can.
As high as you can.
If you can go straight up, great.
Coaxial antennas come to mind as well.
You certainly can't beat simple wire antennas for cost-effectiveness.
73 es gud dx
H.
NQ5H


"Tom Coates" wrote in message
...
Given a choice between mounting the vertical on the ground with many
radials
and putting it 20 feet up with four radials, which has the lower radiation
angle? What are the other likely effects on performance - noise, RFI on
the
neighbors, etc.?

Tom, N3IJ

"Roy Lewallen" wrote in message
...
For 20 meters, all you need is a piece of wire or tubing that's about
16-1/2 feet high (adjust as necessary). I've done it with aluminum
tubing (you'll have to use aluminium, of course ), with a wire hung
vertically from a tree, and a wire spaced from a 2 X 4 inch or lighter
piece of lumber with TV twinlead standoff insulators. Shouldn't run over
£10 or so, and it will work every bit as well as, or better than, any
one you can buy -- on 20 meters. Feed directly with 50 ohm coax. If you
mount it at ground level, bury up to a dozen or so wires extending
radially outward from the antenna if possible. (I just stretch them
along the ground, "stapling" down where necessary with a short piece of
wire, and let the grass grow over them.) Make them as long as you can,
but there's no point in making them any longer than about 20 feet. If
you mount the antenna above ground, you can use fewer radials -- if the
base is 20 feet up, four will be plenty. If the radials are above
ground, you should make them pretty close to 16 - 1/2 feet long, and
adjust if necessary to get an adequately good match.

Roy Lewallen, W7EL

MAS wrote:
Hi People,

I have been looking around at "off the shelf" HF vertical antennas and
because of the price I am now considering home building one myself.

The only HF antenna I have at the moment is a half size G5RV so there
is
room for change ;-)

I guess my main area of interest at the moment is 20m so the vertical
antenna would be mainly for that band.

Can anyone point me in the direction of any good home brew designs to
save
me re-inventing the wheel so to speak?

The antenna can be mounted anywhere from ground level to the top of a
20
ft
pole at the bottom of the garden. I will be running upto 100w into it
from
an FT-920 via it's built in ATU.

Cost is only an issue in as much I begrudge paying £300 + for an off
the
shelf unit so don't restrict your designs on that front..

I am a bit of a dab hand with the tools too but have no fancy antenna
tuning
devices, so any design will need to be almost resonant from the off if
you
see what I mean.

Here is hoping for some good proven designs.

M.

Radiation angle is essentially the same for both. Mounting it higher
will make it more immune to losses from low, nearby objects. An elevated
one will also probably receive and deliver less interference -- provided
you keep the radials well away from, and not parallel to, mains,
telephone, and other wiring.

Roy Lewallen, W7EL

Tom Coates wrote:
Given a choice between mounting the vertical on the ground with many radials
and putting it 20 feet up with four radials, which has the lower radiation
angle? What are the other likely effects on performance - noise, RFI on the
neighbors, etc.?

Tom, N3IJ