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Old July 17th 17, 11:52 AM posted to rec.radio.amateur.antenna
J.B. Wood[_2_] J.B. Wood[_2_] is offline
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First recorded activity by RadioBanter: Sep 2013
Posts: 45
Default Magnetic receiving loop theory

On 07/09/2017 09:08 AM, Pat wrote:

I'm looking at an ad in QST regarding the MFJ Low-Noise Receiving
Loop. Since I have a lot of noise here, I am very interested in this
topic. However, I have having trouble understanding the theory. My
understanding regarding electromagnetic waves is you can't have one
without the other. RF propogates through space my having the moving
electric field create a moving magnetic field which then creates a new
electric field, etc, etc. How can one exist without the other?

Here's a quote from the ad, "The MFJ-1886 drastically reduces noise
and interference by receiving the magnetic field and rejecting the
electric field". How can a varying electric field from a noise source
not also create a corresponding magnetic field? Is this a near-field
/ far-field thing?

Pat



Hello, and I've commented on this previously. Somehow hams have gotten
into the habit of thinking that loop antennas have to be further
described by the modifier "magnetic". Now, a loop antenna can certainly
be close-in coupled (non far-field) magnetically to a radio frequency
source but in that case the antenna is functioning more as
mutually-coupled inductor, which isn't the same as being subjected to an
incident electromagnetic wave in the far-field (at least several
wavelengths from the transmitting antenna).

Bottom line: We have loop antennas (further describable as shielded,
unshielded, multi-turn, tunable, etc). In all fairness, I think what
hams really mean by "magnetic" is an electrically-small loop antenna,
since as the loop diameter gets smaller and smaller we approach the
textbook theoretical "magnetic dipole". By contrast, hams usually refer
to a "dipole antenna" not "electric dipole antenna". The term
"magnetic" is unnecessary and readily misleading. Sincerely, and 73s
from N4GGO,

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J. B. Wood e-mail: