View Single Post
  #4   Report Post  
Old July 9th 17, 07:13 PM posted to rec.radio.amateur.antenna
John S John S is offline
external usenet poster
 
First recorded activity by RadioBanter: May 2011
Posts: 539
Default Magnetic receiving loop theory

On 7/9/2017 12:53 PM, Jeff Liebermann wrote:
On Sun, 09 Jul 2017 09:08:11 -0400, 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?


No.


No what? Please expand.

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?


The transmitter generates both. You can reduce the sensitivity of a
receiving loop to the electric E field by shielding, leaving only the
magnetic H component. Examples of shielded loop antennas:
https://www.google.com/search?q=shielded+loop+antenna&tbm=isch
and unshielded loop antennas:
https://www.google.com/search?q=unshielded+loop+antenna&tbm=isch

Is this a near-field / far-field thing?



No.


So near-field is not different from far field? The textbooks disagree
with you.


I've been collecting articles on magnetic loops, tuners, theory, and
such in an apparently futile attempt to find the time to design
something. Maybe you'll find these articles useful. Most have
references and links at the end to other magnetic loop articles:
https://sidstation.loudet.org/antenna-theory-en.xhtml
https://www.nonstopsystems.com/radio/pdf-ant/article-antenna-mag-loop-2.pdf
http://www.w0btu.com/magnetic_loops.html
http://owenduffy.net/blog/?cat=31
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
https://frrl.wordpress.com/2009/03/21/limited-space-antennas-the-small-transmitting-loop-antenna/

There's some discussion of E and H fields he
http://owenduffy.net/antenna/PA0RDT-MiniWhip/
which you might find applicable.


Did you read any of the links you posted? You must believe that anything
posted on the Internet is true. Owen Duffy is an exception but you
posted his radiation pattern comparing a vertical and a loop.

You must have a http look-up fetish.