o m g! I wondered when someone would come up with that. Speaking
of course as one who Never Inhaled! Jim K6AESW, or something like
that?
----- Original Message -----
From: Howard Kaufman <[log in to unmask]
To: [log in to unmask]
Date sent: Sat, 1 Sep 2012 01:47:38 -0500
Subject: Re: Description of a J Pole antenna
Other uses?
Never thought of it, but you could make a UHF water pipe j-pole
into an
effective bong!!! Nice way to hide a pipe! LOL!!!
----- Original Message -----
From: "John Miller" <[log in to unmask]
To: <[log in to unmask]
Sent: Monday, August 27, 2012 8:02 PM
Subject: Re: Description of a J Pole antenna
I had a real nice one made out of water pipe, I built it when I
was in
college to use in the dorm, then it found various other uses,
like as a
scanner antenna for a long time but it was stolen at my last
apartment. I
had it in the storage unit and the first time it was broken in
to that was
stolen. One of those things I know who did it but couldn't
prove it. Then
people wonder why I'm so anal about locking everything up since
then. when
my room for ham radio is built over here, that will be locked as
well.
----- Original Message -----
From: "Ronald E. Milliman" <[log in to unmask]
To: <[log in to unmask]
Sent: Monday, August 27, 2012 8:49 PM
Subject: Description of a J Pole antenna
Howard,
several days ago you asked if one of us could describe a J Pole
antenna
to
you in enough detail so you could build one. Well, I will try.
Here it
goes...
construction for a 2 meter J Pole :
First, imagine the print letter J . This represents the shape
of the
antenna. It has one long side and one short side all connected
at the
bottom or said another way, one continuous length of conductor
shaped
into
a J.
Now turn or flip the J backwards as if you were writing it with
the short
side on the right rather than on the left. I say this simply
because
this
is the way it is usually shown in the ham mags and on most web
pages.
The J is one single "conductor" in the shape of a J.
From the top of the long side of the J to the bottom, for 2
meters, is
about 58 inches long before it turns horizontally a couple of
inches and
then goes vertical for about 19 1/4 inches. So you have a total
length of
about 77 1/4 inches forming a single J shape.
The center conductor of the coaxial feedline is attached to The
long
section of the J Pole and the braid or shield of the feedline is
attached
to the short section. These feed points for the coax are spaced
up from
the bottom of the J or antenna about two inches, and they need
to be,
initially, adjustable , until you find the optimum tap or
feedpoint that
gives minimum SWR. So, do not make a permanent feedline
connection yet.
Once you have these feedpoints adjusted to produce minimum SWR,
you can
solder them for a permanent connection.
Again, the shield of the 50 ohm coax is attached to the short
section
about
2 inches up from the bottom.
The center conductor of the 50 ohm coax is attached to the long
section
about 2 inches up from the bottom. Both the center conductor
and the
shield
should now be side by side on the vertical elements equal
distance from
the
bottom. One on one vertical side and the other on the other
vertical
side.
BOTH are connected equal distance from the bottom of the antenna
and are
adjusted up or down equally for lowest swr. This is the tricky
part. Some
method of making temporary connections for tuning will be needed
or they
can just be tack soldered for testing and tuning.=20
For tuning, you can mount the J Pole on top of a short pole, a
length of
PVC, a push-pole, etc., or you can mount it on a temporary
support like a
wooden ladder.
Then, once you have it tuned, you will need some method of
mounting the
antenna to a mast, pole, etc in your final installation.
Most builders just add about 15 to 20 inches to the long side at
the
bottom
for mounting.
This extra length becomes invisible to the operation of the
antenna;
thus,
not effecting its operation. So, it can be metal tubing for a J
pole.
Adding this length would make the long side about 58 plus 15
inches =3D
73
inches...or
58 plus 20 inches =3D 78 inches.
=20
Of course, you want to mount the antenna in a location about 1/2
wave
length away from any metal surface near the antenna in any
direction
except
the bottom of the antenna.
The lengths and spacing of the J element is not very critical
due to the
variable tuning section. The main thing is to get the final swr
down as
low
as possible.
Also, it is recommended to add about 4 or 5 turns of coax in a
neat coil
with coils side by side at the bottom of the antenna making an
air
choke=9D
out of it to keep stray rf off of the coax outer conductor.
It is a challenge to describe something like this, but there you
have it.
I hope you are able to visualize it well enough to take a shot
at
actually
building one. Alternatively, they are available to purchase
either fully
assembled or the parts that you can put together yourself. =20
Ron, AC4HM
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