Re: Sleeve dipoles

In article <1r5178a.10eyjis13gf62kN%liz@poppyrecords.invalid.invalid>,
liz@poppyrecords.invalid.invalid says...

 

The bottom  dipole half is never grounded. Another name is coaxial
 antenna. Usually you find them in marine application because of
 the counter poise.

 
Suppose the feed point had a 1:1 isolation transformer, there would be
no reason why the dipole couldn't be grounded at any point alog its
length.  The same isolatio could be achieved by a quarter-wave line.
 
 
 

The bottom half can not be grounded no matter what except at the feed
point maybe.  The sleve dipoe can be thought of as a ground plane with
the elements just folded all the way down instead of down at a 45 deg
angle that makes the impedance near 50 ohms.  It is usually mounted with
a mast that goes to the feed point and it can be either a conductor or
nonconductor.  This pipe can then be fastened to a conductor or
nonconductor.

While a coax dipole can be made of a coax cable with the braid just
folded back over the outer insulation it may not work very well due to
the closness of the brade and the quality of the insulation.