I made one of these out of RG58 for portable operation by striping off the
jacket of the coax much longer than 1/4 wavelength and then working the
shield down over the jacket below it. That way the feedline is inside the
lower half of the dipole and is in a low field area. I put a current balun,
(ferrite beads) at the point the coax came out of the shield. It was a bit
of a struggle to do and you need more shield than you would think (start
very long) but its easy to do in the end. I didn't water proof the braid
over the jacket but one could cover it with tape or a plastic tube. Anyway
after the braid is folded back over the jacket its then tuned just like any
other dipole.
Also if your not going to run high power, the PAR makes an end feed half
wave antenna that has a matching unit at the feed point.


--
John Passaneau, W3JXP
Penn State University


"Robert Spooner" wrote in message
...
Alex,

Solder a quarter wave length of wire to the center conductor of the coax
with a loop at the end of the wire to attach your line to raise it. A
quarter of a wavelength from the wire end of the coax, coil enough of
the coax to form an RF choke. (I think the ARRL Antenna Handbook has the
information you need about how many turns and what diameter to make the
coil.) Seal the end of the coax to keep out moisture. Then hoist the
antenna up and you have a coaxial sleeve antenna.

73,
Bob AD3K

Alex wrote:
Has anyone tried building a 1/2 wave coaxial sleeve antenna for 40m? I
have
a large tree with a branch at 70' and i thought i'd pull the antenna up
with
a rope. Should i make the sleeve out of copper pipe? A 1/2 wave
vertical
would be a nice antenna for 40m and i thought a coaxial sleeve antenna
would
give me a great feed impedance. Any thoughts? The coax are 100' of
RG8.



--
Robert L. Spooner
Registered Professional Engineer
Associate Research Engineer
Intelligent Control Systems Department

Applied Research Laboratory Phone: (814) 863-4120
The Pennsylvania State University FAX: (814) 863-7841
P. O. Box 30
State College, PA 16804-0030