dansawyeror wrote:
All,

I have been using an 80 meter loaded vertical for a couple of years with
moderate success. The ground system is a dozen 'untuned' radials 40 or
so feet laying on the ground. The feed line is about 100 feet of RG-8
coax. The SWR in the shack is about 1.1 to 1.

I have done some research on the antenna and based on it parameters it
should have a radiation resistance of about 4 Ohms. This says that the
coil and ground are absorbing on the order of 45 Ohms. This is 10db
performance loss.

I have limited space and the most common solutions are not available to
me. From a practical perspective it would seem to me that building a 40
foot center feed loaded dipole and putting it in the attic or on the
roof would probably perform somewhat better.

Is this a reasonable assumption?


I'm not sure you can count on that. You'd still lose some in a
matching/loading network, there'd be a lot of ground loss because of the
low height, and absorption of some of the power from conductors in the
house might occur. It wouldn't hurt to try, but leave your vertical up.

Would burying the radials and connecting them to several 4 square foot
buried screens substantially help the ground system?

Just about anything you can do to increase the conductivity of the
ground system, particularly close to the antenna, will help. Using
screen is one thing. Burying the radials won't help. Adding more radials
and making them longer will help. Unfortunately, making a few radials
longer doesn't do much, and adding a bunch of short radials doesn't do
much either -- you really have to do both to have a big effect. If
possible, connect to any other nearby buried conductors such as metallic
water pipes.

The other thing you can do to improve the efficiency is to increase the
radiation resistance of the antenna. You can do this of course by
increasing the height of the antenna. Moving the loading coil upward
will help, too, although you'll need more inductance. (The coil still
won't be a major part of the overall loss, though.) A top hat is better
yet. You can also increase the radiation resistance by making your
antenna fatter. Use multiple wires in parallel, spaced about as far as
you can, either along side each other, or fanned out, converging at the
bottom.

Finally, if you've got room, you can improve your overall efficiency by
about 3 dB by putting in another identical antenna/ground system
somewhere nearby and connecting the two in parallel.

Roy Lewallen, W7EL