View Single Post
  #15   Report Post  
Old July 11th 17, 04:50 PM posted to
rickman rickman is offline
external usenet poster
First recorded activity by RadioBanter: Nov 2012
Posts: 989
Default Magnetic receiving loop theory

Bartolomeo wrote on 7/10/2017 7:31 PM:
On 2017-07-09 o 15:08, Pat writes:

understanding regarding electromagnetic waves is you can't have one
without the other.

Yes, every transmitting antenna creates perturbance that spreads around as
electromagnetic (EM) wave with electric and magnetic component but...
In the _near field_, magnetic antenna creates mainly the Magnetic component
of the field and Electric antenna (in ex. dipole) creates electric field.
The same goes to receiving. Shielded magnetic loop is quite deaf to M
component of the EM field.

I think you mean the shielded loop is "deaf" to the electric field.

(Un)fortunately most of the local noise sources create perturbance in E
field. Therefore chances are that magnetic loop will be in some degree
immune to them. The other noise sources may or may not be in the near field
range but the furher away they are the less they add to the total noise level.

Of course you've read this?

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?

In the near field the antenna itself will generate a field (either magnetic
or electric depending on the design). This field falls off rapidly with
distance. The antenna also generates an EM wave which radiates and is
dominant at distance (far field).

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?

The ad copy isn't saying there is no magnetic field from the noise source,
but most noise sources are close enough to be near field with a much
stronger E field than the magnetic component. This is *very* much a
near/far field thing.


Rick C