"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"..


Bob D. -

Please don't take my comments as being negative about a J-Pole. I happen to
like them for other reasons. They can be made very rugged. The few I made
started out as a 30-foot mast. 3/4 wavelengths down from the top I mounted a
horizontal metal bracket. To that I mounted a vertical 1/4 wave tube. I then
used automotive hose clamps to connect a 1/2 wavelength piece of coax near
the bottom just above the horizontal bracket. I adjusted the connection
point of the coax to find the lowest SWR point and then replaced the 1/2
wave piece of coax with my longer lead-in. I put some weatherproofing on the
coax.

I ran 10 gauge wire from my nearby ground rod over to the bottom of the
mast. What I like about this arrangement is that the entire assembly is
grounded. I once had a nearby lightning strike cause my IC2AT to block
signals for several seconds while I was listening to a local repeater with a
home-made ground plane. Charge buildup, I guess. That never happened with my
J-Pole. That thing worked flawlessly for several years until I replaced it
with a commercial dual-band (expensive) antenna.

Have fun.

73,
John