Topband: Short Bogs

[Tom W8JI]

> 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