On 10/14/2015 02:34 PM, rickman wrote:
I just read the wikipedia article on small loop antennas and it seems I
was laboring under a misapprehension. I thought receiving loops were
"magnetic" because they were shielded (this is often stated in various
web pages about constructing such loops). But the wikipedia article on
small loop antennas says the nature of a small loop is to not be very
sensitive to the E field in near field.

So if the shield has little to do with rejecting near field electrical
noise, what does the shield do? A lot of antenna designs make a big
deal of the shield. So I assume it must be a useful addition to the
small loop antenna for some purpose.

Hello, and that seems to be ham radio jargon. Hams seem to think the
adjectives "magnetic" and "electric" are needed when referring to loop
and dipole antennas, respectively. Textbooks on electromagnetics and
antennas don't use those terms except in the case when discussing
theoretically small radiators, i.e. "magnetic dipoles" and "electric
dipoles".

My hypothesis on the ham terminology is that a loop is viewed as an
inductor. That's OK for close-in (non-radiative) mutual coupling to
some source but when you're several wavelengths away (in the far field)
then the loop (or dipole antenna for that matter) responds to the
electromagnetic field (the electric and magnetic far fields can't be
considered separately). The fact that an axis of either antenna lines
up with the electric or magnetic field vector in the far field is moot.
Does this mean that the loop doesn't have inductance? Of course not
and it plays a role in establishing the feedpoint impedance of the loop
at the operating frequency. Now if folks would just stop using that
word "literally" so damn much...

Sincerely, and 73s from N4GG0,





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J. B. Wood e-mail: