On Apr 1, 10:43 pm, dansawyeror wrote:
All,

I am interested in building a tuned counterpoise system. The antenna is
a screwdriver and the frequency of interest is 3970 kc. Reg's c_poise
program predicts a reasonable set of parameters, a 10 foot 'wire tube',
one meter up, and a coil in the range of 50 uH. The program predicts a
'ground' in the range of 5 Ohms.

Is that a base load? Seems to be using a 50 uH coil.. I'd be thinking
70-80 uH
for a short center load...?

How oversimplified is this?

The current ground measures over 40 Ohms and the system is just over 5%
efficient. To go from a ground of 40 Ohms to one of 5 Ohms gives the
potential of a system efficiency approaching 50%. An 8 to 1 increase in
efficiency could yield a 9 db improvement. This is worth some serious
experimentation.

Thanks for you thoughts and analysis in advance - Dan

I'm just wondering why you want to use this type of antenna. Seems
like a
lot of work involved to get semi decent performance vs even a simple
dipole.
IE: why only a 10 ft whip? Is this for some type of portable use?
To get a low ground loss you will need quite a few radials when near
the ground, and using the short antenna makes things even more
critical.
If I had a mobile whip, I'd just as soon mount it on a car, and run
coax to it,
vs other options.
If this was at the house, I'd try to use a taller vertical, use top
loading
wires, etc.
But most of my 75m stuff is fairly local NVIS yik yak, so I'd just as
soon be
on a dipole.
You say the mount is three feet up... Might as well be on the ground
as far as the number of radials needed. They can be resonant, and
there
will be a slight advantage over non resonant radials laying on the
ground,
but nothing earthshaking. Don't expect high efficiency with 2-4
radials
strung 3 ft in the air. You'll need 30-60 just to get in the medium
performance
mode, and you would still be in the mud vs the usual dipole..

Dunno...I may be confused... But I don't see it..If I was going to get
on
75m, I'd stick up a coax fed dipole and be done with it. It would
smoke
that short vertical running over most any counterpoise you might cook
up.
I can live with a short vertical when mobile because I have no choice.
But otherwise, I can think of better antennas for that band. But I
don't
know if you work NVIS or DX.. Even with DX, a vertical will need to
be
fairly decent to compete with an efficient dipole at even 25-35-45 ft
up,
which is pretty low height in wavelength for 75 meters. I work DX on
75m
with 100w no problem at all using a coax fed dipole at about 40 ft.
This is not to say I don't like verticals.. I do. But I would try to
run a bit
more robust version than a screwdriver unless actually mobile..
IE: a simple inv L or T made of wire "60-65 ft" thrown over a tree
will
usually outdo the short whip. I like the "T" better for a pure
vertical
pattern with little horizontal componant.
But I'm much more likely to use a T vertical on 160m than I am 80..
I'm almost always on the dipoles on 80m. Well, actually a turnstile
at the moment.. Crossed dipoles..
MK