Richard,

I think you are confusing the Isotron by Bilial with the Isoloop
formarly made by AEA. The Isoloop was a small loop antenna tuned with
a large remote variable capacitor like you describe. The Isotron is
just a large fixed capacitor (you can make a slight manual tune to it,
not remote tune like a magloop) and a muliturn solenoid inductor. I
serves as nothing more than a lossy load to dump your power into. The
actual antenna is the metal mast you are supposed to attach the
Isotron to. The antenna is essetially a small radom wire antenna
composed of the metal mast and/or the outside shield of the coax
attached. Whatever power is not lost in the Isotron, travels on the
metal mast and outside shield of the coax and couples into your house
wiring, television and neighbors appliances, and oh yes, a small
amount is radiated. It works essetially the same as the supposed
cross field and eh antenna. A large LC tank connected to a short
random wire antenna composed of the ground lead and outside of the
coax shield. If you choke off the current from the ground lead and
outside coax shield, you essentially have an unshielded dummy load.
Thats all there is to them.

73,
Dan

(Richard Harrison) wrote in message ...
Henry Koleanik, WD5JFR wrote:
"Anyone really know theory behind these things?"

The Isotron is a small tuned loop. Tuning gets rid of reactance which
would cripple performance were it not removed from the loop.

A small loop has a null perpendicular to the plane of the loop. Energy
suppressed in directions of the loop`s axis is radiated in the plane of
the loop giving a directivity power gain of about 1.5 (not dB, where
it`s just under 2 dB gain) over an isotropic radiation in the plane of
the loop as in other directions as well.

The bad news is that even made with a large surface area, the small
loop`s loss resistance looms large as compared its radiation resistance.

The 3rd edition of Kraus` "Antennas" is a clear source of single-turn
circular loop information. Fig.7-10 on page 209 gives radiation
resistance versus loop circumference. Fig. 7-11 gives directivity.

If radiation resistance were 0.5 ohm and r-f resistance were 0.5 ohm,
efficiency would be:
0.5/1=50%

Kraus has Fig. 7-17 on page 217 which gives radiation efficiency as a
function of frequency for a 1-m-diameter single-turn 10mm copper tubing
loop in air. At 1 MHz, the loss is about 40 dB. At 10 MHz, the loss is
about 6 dB. The radiation resistance of the loop is rising more rapidly
than is the loss resistance as frequency goes up. The loss is enormous.
This is ok for reception in most cases, but it`s very dear for
transmitting.

Best regards, Richard Harrison, KB5WZI