"Owen Duffy" wrote in message
...

The failure of the sleeve to effectively decouple the dipole is the
reason why several antennas don't work as thought. King gives some hints
that the relative diameters of the conductors bears on operation.

Owen


I made a sleeve dipole cut for 375 MHz for listening to the Blue Angels in
flight at NAS Miramar, c. 1992. It worked, but, heck, we could see them
most of the time. I was in Coat Hanger Territory. By the way, the Blue
Angles say very little in flight. :-(

This thread got me thinking. If three or four tuned radials were added,
would this be a better approach? Yes, I realize it gets toward a lot of the
standard commercial monopole antennas, with their 45-degree-down radials. I
mention this because such radials could be added and still keep the builder
in comfy Coat Hanger Territory -- that is, a very light, casual,
cobbled-together antenna -- but something that works a bit better and helps
the decoupling.

Frankly, I understand what it is to buy something and what it is to build
something; I'd rather build. It keeps me off the street. :-)

"Sal"
(Kd6VKW)

"Sal" wrote in :

...
This thread got me thinking. If three or four tuned radials were
added, would this be a better approach?

A set of radials helps to decouple the feedline, in this case, you would
place them a quarter wave below the bottom of the sleeve.

Ok, you have noted commercial implemenations of this idea... yes it is
done. The quarter wave between the radials and the bottom of the sleeve
carries significant current, ie it affects the pattern and gain.

And still, decoupling is not perfect, though much better.

Whilst the OP's design looks like it is simple, in my experience it is
not. Whilst I have had a lot of success with coaxial dipoles where the
sleeve was three times or more the diameter of the inner element and
substantially air dielectric, I have had little success the the cheap
and nasty approach of applying braid over a vinyl jacket and trying to
adjust it for low common mode feed line impedance and low VSWR. I am not
saying it is impossible, just not as easy as a ground plane!

Owen