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Old May 18th 05, 07:05 AM
Richard Harrison
 
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Henry Kolesnik wrote:
"If I wanted to measure the difference between the two fields how would
I measure the electric field?"

If this is the radiation field, not the reactive field, it would make no
difference if you measured the electric field or the magnetic field, as
they contain the same quantity of energy. In fact, the energy is
identical as one field begets the other field. That`s "The Secret of
Propagation".

That does not mean the fieldfs can`t be separated. It is easy. Enclose
your loop in an effective Faraday screen. This screen prohibits
electrostatic coupling to the loop, but freely allows magnetic coupling.

Faraday screens are not rare. Nearly every medium wave broadcast station
uses a Faraday screen at every tower between the primary and secondary
of an air-core coupling transformer. Because, without the screen,
capacitive coupling to the tower would favor harmonics of the broadcast
frequency over its fundamental frequency and make compliance with FCC
rules difficult. The Faraday screen is also an excellent lightning
protector.

It`s just as easy to allow only capacitive coupling. Simply put a
circuit to be kept from magnetic coupling in an enclosure which is
completely enclosed in a metal structure (sealed like an expensive
signal generator except for one small hole). Use a capacitor through the
small hole to couple to the outside world. Only the electric field via
the capacitor will influence the circuit in the box.

R-F will not penetrate a metal shield, unless it`s special like the
sliced-up Faraday screen. Then, it`s only the magnetic field which
penetrates. Skin effect requires r-f to flow only on the surface of good
conductors to any appreciable depth.

Best regards, Richard Harrison, KB5WZI



 
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