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Old December 3rd 09, 09:54 PM posted to rec.radio.amateur.antenna
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Default Faraday shields and radiation and misinterpretations

On Thu, 03 Dec 2009 13:37:05 -0800, Richard Clark
wrote:

Yes indeed. If those wires were not, in themselves, decoupled; then
they became radiators.


Further discussion about these wires allowing RF to slither through
what would ordinarily be impenetrable holes.

Those holes, whose circulating currents prohibit any coupling of
fields through them, as long as they are very small in relation to the
wavelength, can turn into free-flowing fountains of power with some
rather simple additions.

As mentioned, merely pass an insulated wire through the hole. If that
wire reaches into the interior where an RF field presents a very high
potential difference to the Faraday shield, then you have a capacitive
coupling to the exterior of the shield, through the hole, along that
wire. On the other hand, if you loop that interior wire back onto the
interior surface of the shield, AND that loop resides within the RF
field where it presents a very high magnetic component; then you have
an inductive coupling to the exterior of the shield, through the hole,
along that wire. Simply terminate the outside extension of that wire
to a suitable load, observing the conventions of matching, and remove
as much power as is practicable.

This is nothing more complex than the usual design conventions already
discussed under the coaxial transmission line considerations in the
post this derives from.

The point of this aside is to remark how easily (or difficulty) the
Faraday shield can be corrupted through indifference to first
principles.

73's
Richard Clark, KB7QHC
 
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