"Jim Lux" wrote in message
...
John KD5YI wrote:
"JB" wrote in message
...


The 1/4 wave ground plane has a useless pattern. Main lobe at about 30
degrees above horizon, but broad enough to be usable and simple to
build.


The quarter-wave antenna's height above ground has much more to do with
the elevation angle than the fact that the antenna is a quarter-wave
ground plane. Using EZNEC, I see that a quarter wave antenna situated 3
wavelengths above real/high accuracy ground of medium characteristics
has a main lobe 4 degrees above the horizon. At that angle, the gain is
5.1 dBi. You can confirm this if you have a copy of EZNEC.

John

If you're just looking for a portable vertical antenna, just a wire on
the end of the coax, and hanging it up, works pretty well. The shield of
the coax (outside surface) serves as the other half of the dipole.
Heck, it will have a bizarre pattern, and couple RF everywhere, but
you're talking about an antenna you're hanging out of a hotel window or
something.. You're not doing earth-venus-earth radar tests... you're
just getting the antenna away from where you are sitting to "outside"..

If you are using such construction, why not just build a coax type of
colinear? It isn't so difficult to add a section of outer shield for
decoupling. Have you priced PA hybrids lately?

BTW any degree uptilt is usually worthless unless you are deliberately
limiting coverage to the horizon. and anything significantly higher in
elevation is line of sight anyway. For ground level base station or
repeater that covers a localized area, a J-pole is attractive because of its
broad pattern that allows numerous reflections through and between the
buildings. I've been told that an upside down ground plane ought to work
better, but it doesn't