RadioBanter - View Single Post

May 16th 06, 04:16 PM posted to rec.radio.amateur.antenna

wrote:

The experiment I did years ago used a copper wall in a one or two foot
square thin sheet.

I made a link on one side through a high power 50 ohm load resistor.
This allowed me to run significant known current through the resistor
(and link) from a regular HF transmitter.

Using two probes, one a sensitive low voltage dial light bulb with two
prongs soldered on and the other a multiple turn loop with diode/meter
indicator, I could roughly check current in multiple places on both
sides of the sheet.

It was very easy to see where the magnetic field (and current) goes. It
does not pass through the wall. It's quite amazing to see how even a
direct soldered connection on one side will not produce current (and a
magnetic field) on the other side.

I encourage Yuri to add this experiment to the ones I suggested, or just
do this one. Understanding what happens to the currents and fields in
the presence of a shield is essential to understanding "shielded" loop
operation, and his statement about magnetic fields and non-ferrous
shields shows that he lacks this understanding. Any explanation based on
the mistaken idea that a non-ferrous shield is transparent to a magnetic
field is bound to be seriously flawed.

Roy Lewallen, W7EL