Here is some antenna theory to read to answer your questions
URL:
http://k9erg.tripod.com/theory.htm

--
Caveat Lecter

"Caveat Lector" wrote

Here is some antenna theory to read to answer your questions
URL:
http://k9erg.tripod.com/theory.htm

Nice site. Except for the inaccurate advice warning of disastrous effects
from operating a J-Pole w/o a BalUn. I use neither a BalUn nor any
coiled-feedline as a choke. If my feedline is radiating, it's the most
efficient feedline radiator ever made, getting loud and clear 100 mile
coverage on VHF Marine between other high sites, and surface contacts
between 20-30 nautical miles depending on height of vessels antenna.
Another misconception about J-Poles is from at least one web-site offering
plans, in which the offerer warned against grounding the antenna. Dangerous
and wrong of course, as the antenna and its mast should be grounded and
performs very well as such. The stub-capped tops of a copper-pipe J-Pole
antenna at the highest point of a structure will indeed be an air terminal
for lightning that was going to strike that immediate area anyway. Maybe my
lightning down conductors heading 180 degrees from the J-Pole to series of
ground rods are the SECRET G.
--
Users considering a static and lightning-grounded (and un-choked) J-Pole
should make sure the British did not already invent/patent this form of
improvement to the J-Pole radiation pattern. ;-)
--

73,
Jack

Jack Painter wrote:

Nice site. Except for the inaccurate advice warning of disastrous effects
from operating a J-Pole w/o a BalUn. I use neither a BalUn nor any
coiled-feedline as a choke. If my feedline is radiating, it's the most
efficient feedline radiator ever made, getting loud and clear 100 mile
coverage on VHF Marine between other high sites, and surface contacts
between 20-30 nautical miles depending on height of vessels antenna. . .

The problem is that without the balun, the feedline is part of the
antenna. So anyone trying to get the same results as you do has to use
the same length of feedline, position it the same, and maybe even ground
his rig the same way you do. (That is, have the same path from the rig
to the Earth through the power wiring.) If he does it differently and
happens to not be as lucky as you, he could take a bit of a beating in
field strength. And both of you could be running the risk of causing RFI
if you're running significant power and your feedline runs close to
house or telephone wiring.

If a balun is used (actually, two are likely necessary, spaced about a
quarter wavelength apart), only the J-Pole will radiate, and the user
won't have to worry about lucking out and having just the right feedline
and orientation.

I think the reason some people love J-Poles and some hate them is that
some, like you, have been lucky with feedline length and placement and
some haven't. I prefer to depend on design rather than luck to make my
antennas work, but lots of folks are perfectly happy to just roll the dice.

Roy Lewallen, W7EL

"Roy Lewallen" wrote
Jack Painter wrote:

Nice site. Except for the inaccurate advice warning of disastrous
effects
from operating a J-Pole w/o a BalUn. I use neither a BalUn nor any
coiled-feedline as a choke. If my feedline is radiating, it's the most
efficient feedline radiator ever made, getting loud and clear 100 mile
coverage on VHF Marine between other high sites, and surface contacts
between 20-30 nautical miles depending on height of vessels antenna. . .

The problem is that without the balun, the feedline is part of the
antenna. So anyone trying to get the same results as you do has to use
the same length of feedline, position it the same, and maybe even ground
his rig the same way you do. (That is, have the same path from the rig
to the Earth through the power wiring.) If he does it differently and
happens to not be as lucky as you, he could take a bit of a beating in
field strength. And both of you could be running the risk of causing RFI
if you're running significant power and your feedline runs close to
house or telephone wiring.

If a balun is used (actually, two are likely necessary, spaced about a
quarter wavelength apart), only the J-Pole will radiate, and the user
won't have to worry about lucking out and having just the right feedline
and orientation.

I think the reason some people love J-Poles and some hate them is that
some, like you, have been lucky with feedline length and placement and
some haven't. I prefer to depend on design rather than luck to make my
antennas work, but lots of folks are perfectly happy to just roll the
dice.

Roy Lewallen, W7EL

Hi Roy, thanks for the comments. It certainly may be luck as you say, but if
so it is exceptional luck ;-) 25 watt marine transceivers rarely perform
as well as mine does in this setup. So well that it is highly unlikely that
the sixty odd feet of 9913 feedline radiates much if at all. The original
configuration had the horizontal (with later vertical drops to ground rods)
lightning down conductors added last year, replacing a simple static ground.
Coaxial lightning surge arrestor was also added, with shield-grounding. None
of these alterations made any noticeable change in the antenna's long range
receive and transmit performance. There never was any connection between the
transceiver and AC power, using instead a 12vdc deep cell battery with a 12v
charger floating the battery.

73,
Jack Painter