In article . com,
"RHF" wrote:

Telemon,

How does your Coax Cable Loop Antenna differ from this one ?
.
"Low Noise Receive-Only Coax Cable Loop Antennas
for 160 - 10 Meters HF Bands"
http://www.greertech.com/hfloop/mymagloop.html
The so called GREER TECH "Coax Loop" Antenna.

Three things:

1. My antenna is larger. My larger antenna will develop
more energy from a passing wave.

2. The shield opening is on the end on my antenna instead of the middle
of the loop. Technically the center opening should be better balanced
but I did not notice any difference.

3. My antenna has a termination resistor, which flattens the response.
You probably would not want it on a smaller loop.

Small point on the web page The comment "RF energy now travels from the
braid's outer skin to the braid's inner skin at the gap which then
couples to the center conductor" is not quite right. The shield
technically is not the antenna, the center conductor is the actual
receiving element. The coax becomes a magnetically sensitive antenna as
the shield blocks the electric part of the passing EM wave from it. The
shield develops a current from the voltage part of the passing EM wave,
which generates a secondary magnetic field that couples to the center
conductor in phase with the magnetic part of the passing EM wave. The
center conductor then sees a 2X magnetic field from a passing EM wave
where a local induction field will not cause this to happen. If the
coax is grounded on both ends then the current on the outer shield will
be opposing and cancel out instead of being in phase and having the
resultant gain.

Makes you appreciate that it is important to have a good ground on both
ends of a coax cable. If you have a bad ground on one end you have a
pretty good antenna.

The author of the web page is doing other things with the loop like
tuning them for transmit, which we don't care about here but he also
mentions a 2 turn loop. I defiantly don't recommend this as some of the
shield will end up floating because it must be separated on every turn.
For a shielded loop stick with one turn. Another reason would be cross
sectional area will be larger with one turn.

I neglected to mention loop gain is in the plane of the loop and the
null is perpendicular to it as it would be for any electrically small
loop.

--
Telamon
Ventura, California