"Tom Bruhns" wrote in message
m...
The "shield" is actually the antenna, and the gap in the "shield" is
the feedpoint of that antenna. You will do well to make the "shield"
out of a good conductor, and to get the benefits of rejecting
vertically-polarized electric fields generated nearby, you should make
the antenna very symmetrical. See the discussion in King, Mimno and
Wing's "Transmission Lines, Antennas and Waveguides." I think I have
a .pdf file of the relevant section somewhere. I particularly like
that one for its qualitative explanation, clearly presented. I've
seen other decent explanations in places like Johnson and Jasik's
antenna book. The explanations in such texts that I've seen all
agree.

A key advantage of the "shield" is that it simplifies the task of
making the antenna symmetrical, though I've seen a lot of old ARRL
pubs that completely miss that point. If you realize that that's what
you're trying to accomplish in the "shielded" construction, you'll
find you can do quite well with a multi-turn "unshielded" loop, too.

Cheers,
Tom (one with a last name)

Hi Tom (WALN),

I thought the original question related to whether or not the magnetic
field penetrates the "shield".

I have a problem calling the shield the antenna because I have built loops
(144 & 440 MHz) which do not have this classic form of shield, but a
unidirectional screen, and good nulls off both sides. I made the shield
from a series of vertical wires connected to a conducting strip only at the
bottom.
I also wonder about the symmetrical concept as a standard "Hazeltine"
loop had the opening of the shield at one end near the bottom, near the
feed.
I suspect that a symmetrically constructed loop will have less
electrostatic response, however. This seems to make sense. Then there is
the matter of the practicality of construction. If it is easier to make the
loop unsymmetrical and shielded, then that's ok.

73, also with a last name,
--
Steve N, K,9;d, c. i My email has no u's.