Shielded loops are not shielded, and neither are shielded ground leads or
even BOG's. The outside is always the naked antenna, just like a single
unshielded conductor.
One more additional comment that came up in email that is useful as general
information on "magical antenna tricks".
The use of coax cannot change the electrical length of the antenna mode by
way of the cable velocity factor. The only RF currents (where the shield is
more than several skin depths thick) that can exist inside a shield are
transmission line or differential currents. All antenna currents are on the
outside, away from the dielectric.
Some articles claim coax velocity factor can be used to physically shorten
(electrically lengthen) an antenna, even dipoles, but there is always a
serious mistake or misunderstanding at work.
For example:
http://www.hamuniverse.com/10metercoaxdipole.html
If we want to make an antenna electrically longer through cable velocity
factor, it can't be done by the insulation slowing the wave inside the
shield.
73 Tom
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Stew Perry Topband Distance Challenge coming on December 29th.
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