Topband: RX Loops

[Tom Rauch]

> I stated, and PROVED, that when this loop is in the far
field of the TX
> antenna (which we approximate as an illuminating plane
wave) it indeed is very
> different than other antennas. Namely, it responds only to
the magnetic component
> of that field. An electrical dipole would respond only to
the electric
> component, and that is a significant difference. It can be
used as the basis for
> enhanced designs which rely on selective shielding of the
E or H component.

In the farfield every antenna looks exactly the same so far
as field impedance goes. The response is only to the EM
field, not to a "magnetic" or "electric" field. The ratio of
electric to magnetic component, or field impedance of the
antenna, is identical regardless of the source.

It's also well known and established taking the time-varying
electric field to zero causes the time-varying magnetic
field to go to zero right with it.

Anyone doubting this only needs to borrow a standard BC
field strength meter and have a look at the scale. Such
meters are calibrated in (milli- or micro-) volts per meter,
an electric field term. The antenna in the meter is a small
loop. It is the very fact that the electric and magnetic
field ratio of radiation is ALWAYS in a proportion
established by the impedance of the media propagated through
(freespace is ~377 ohms) that allows a small "magnetic loop"
to accurately measure electric field intensity. BC field
strength meters that read in V/m are actually calibrated in
volts per meter with a current carrying conductor placed
next to the loop!

73 Tom