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Author Topic: Magnetic Loop for noise reduction?  (Read 4551 times)
WB6BYU
Member

Posts: 13341




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« Reply #15 on: March 25, 2012, 07:50:51 PM »

Quote from: KW5B

An electrical signal cannot get inside the sheilded box...  

But equally obvious a magnetic signal can... 

...

No one seems to realize or want to admit that although electric properties and magnetic properties are linked, they have different properties. 




And what we are trying to receive is an electro-magnetic wave.  It needs both
parts to function.

I spend a lot of time in a screen room at work.  Sure, you can wave a magnet around
one side of it and detect the changing magnetic field, or wind a coil on each side of
the copper mesh and pass AC current though it.  But my cell phone loses coverage
when I close the door, and you can't listen to the ball game on your AM radio inside
even though it uses a loop antenna.

If a "magnetic" loop really responded to magnetic fields, you would be able to.  But
the term "magnetic loop" is a misnomer - it still responds to electromagnetic
fields like any other antenna.  The ratio of the two fields may change somewhat,
but you still need both components.

Even though you could get a magnetic field inside the screen room, you can't get
radio signals.  (Unless someone leaves a hole, or fails to filter an incoming wire.)
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K4FMX
Member

Posts: 17




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« Reply #16 on: March 26, 2012, 08:19:52 AM »



Doesn't your post prove my point.  An electrical signal cannot get inside the sheilded box.  That's is the reason for using them.  No argument.

But equally obvious a magnetic signal can.  Two magnets place on opposite side of a non magnetic metal.  Move one and the other moves.  If they are electromagnets and you vary the  voltage on the outside magnet  the voltage will be mirrored by the voltage created by the electromagnet on the inside.  That's elementary physics high school physics it is not?   

And if the magnetic loop antenna does indeed operate from magnetic properties, those magnetic signal can quite easily pass through the shielded aluminum, copper or silver box. 

No one seems to realize or want to admit that although electric properties and magnetic properties are linked, they have different properties. 

ljg
kw5b

Why do you think that there is a gap in the shield of the loop antenna? If it worked as you propose, strictly magnetic, then there would be no need for a gap in the shield would there.
A screen room would pass radio signals too would it not if we were only dependent on magnetic properties of a radio signal?

73
Gary  K4FMX
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W1JKA
Member

Posts: 1773




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« Reply #17 on: March 26, 2012, 08:55:22 AM »

    Gee,I don't know how the dogs faired,but I have learned more about mag loop antennas in this discussion than I have read about in the two books I have on the subject.Very interesting-thanks  Jim
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