Topband: RX Loops - Some relevant facts
w8ji at contesting.com
Wed May 12 20:03:58 EDT 2004
> This is the basic physics of the small loop as taught to
every EE sophomore.
> It clearly shows that the small loop "responds' primarily
to the magnetic
> field, and for this reason, most field theory people refer
to small loops as
> 'magnetic dipoles.' A short length of single straight
wire, a/k/a an electric
> dipole, responds primarily to the electric field (the
integral of E is NOT 0 along
> the wire). The distinction is very clear.The comments made
by W8JI to the
> contrary are seriously in error. Unless he has some magic
concept hidden in the
> term "field dominant", which to me is vague and not a
standard term within EMF
If you read carefully you will note I said (and always say)
the loop is magnetic response dominant (it also has to have
SOME electric field response) very close to the antenna. We
are actually in agreement with what happens very close to
the antenna, say well within 1/8th wl.
The field impedance of a small loop antenna, however, is
***exactly*** as I described.
I have a graph of the field impedance, which actually comes
from standard corrections that must be applied to the loop.
You can see the field impedance, or ratio of sensitivity to
electric and magnetic fields (or intensity when
At distances beyond 45-degrees (~70 feet on 160 meters) the
small magnetic loop indeed responds more to electric field
than magnetic. We can call the antenna anything we like, but
that's how it works.
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