I have been reading alot on different designs and have read
contradictory information on this. Does nayone here have an opinion?

Also, when building a j-pole, could I run the wire inside the tube.
(Regular jacketed copper wire) to the bottom of the tube to a pl
connector? Or would this mess up the impedance?

wrote:
I have been reading alot on different designs and have read
contradictory information on this. Does nayone here have an opinion?


As I understand it, a J-pole is derived from nothing but an inverted
Zeppelin-antenna. That makes the feedpoint a balanced one and you
need a balun or at least a choke. But as a Zepp-antenna it does not
need any ground just like ordinary dipoles don't. But if you ground
a J-pole the ground needs to be exactly in the middle of the short
in the feed line. For practical reasons most J-poles are not
constructed this way.

Also, when building a j-pole, could I run the wire inside the tube.
(Regular jacketed copper wire) to the bottom of the tube to a pl
connector? Or would this mess up the impedance?


What you are looking for is on YO5OFH, Csaba Gajdos web page he
http://www.qsl.net/yo5ofh/projects/a...ol_antenna.htm
but I didn't try the design myself yet. I might within short.

There is ample of information on J-poles he
http://www.cebik.com/jp1.html

Kind regards, Eike

Eike Lantzsch, ZP6CGE wrote:
wrote:
I have been reading alot on different designs and have read
contradictory information on this. Does nayone here have an
opinion?


As I understand it, a J-pole is derived from nothing but an inverted
Zeppelin-antenna. That makes the feedpoint a balanced one and you
need a balun or at least a choke. But as a Zepp-antenna it does not
need any ground just like ordinary dipoles don't. But if you ground
a J-pole the ground needs to be exactly in the middle of the short
in the feed line. For practical reasons most J-poles are not
constructed this way.

Also, when building a j-pole, could I run the wire inside the
tube.
(Regular jacketed copper wire) to the bottom of the tube to a pl
connector? Or would this mess up the impedance?


What you are looking for is on YO5OFH, Csaba Gajdos web page he
http://www.qsl.net/yo5ofh/projects/a...ol_antenna.htm
but I didn't try the design myself yet. I might within short.

There is ample of information on J-poles he
http://www.cebik.com/jp1.html

Kind regards, Eike
So, does a j pole need to be insulated from the antenna mast?

wrote:

Eike Lantzsch, ZP6CGE wrote:
wrote:
[snip]

So, does a j pole need to be insulated from the antenna mast?

No. For lightning protection grounding is recommended but it does
nothing to the function of the J-pole.

Kind regards, Eike

What about a dual band version?

A J-Pole is a 1/2 wave vertical antenna, that sits on TOP of a U
shaped 1/4 wave matching section.
During construction, the 1/2 wave vertical element AND ONE of the 1/4
wave legs of the Transformer are constructed of the same piece of
tubing. Thus the J appearance and name.

RF is invisible to whatever lies below the Horizontal Member, so
whether the mast is grounded or not would have no impact on the
J-Poles performance. However, the shield MUST be grounded for obvious
reasons.

It is Normal and Proper to RUN the COAX up the center of the mast,
INSIDE the Antenna and EXIT the vertical element at the Horizontal
Member.
If you don't, THEN you will need to stop stray RF that runs along the
coax and/or use a Balun.

When you connect your COAX to the J-Pole:
If it is a MonoBand J-Pole, run the center conductor to the STUB,
leaving the sheild jacket intact up to within about 1/2 inch of the
stub. Then run a wire from the shield horizontal to the horizontal
member and affix this to the vertical.
If it is a Multi-Band J-Pole, the center conductor should be connected
to the Vertical Element and a wire from the shield runs horizontal
over to the stub.

Although a J-Pole will work with the coax connected either way. On
MonoBand J-Poles, having the center conductor going to the Stub
reduces the noise level slightly. It can make a difference when you
are trying to pull in QRP stations.

Using 3 or 4 1/8th wave wires, like a capacity hat, protruding outward
on the top of the vertical element will give the same noise reducing
effect.

TTUL
Gary







verbositized:

I have been reading alot on different designs and have read
contradictory information on this. Does nayone here have an opinion?

Also, when building a j-pole, could I run the wire inside the tube.
(Regular jacketed copper wire) to the bottom of the tube to a pl
connector? Or would this mess up the impedance?

On 07 Jan 2005 12:50:05 EST, am (Gary V.
Deutschmann, Sr.) wrote:

RF is invisible to whatever lies below the Horizontal Member, so
whether the mast is grounded or not would have no impact on the
J-Poles performance.

NEC anylisis I've done doesn't not show that to be true. A j-pole
directly connected at its base to a conductive mast will increase
higher takeoff angles. The worst case is with mast lengths of even
½-wavelengths. With mast lengths of odd ¼-wavelengths produce less,
but, in ether case connecting a j-pole to a conductive mast will
increase high angle radiation patterns.

Danny, K6MHE

Gary V. Deutschmann, Sr. wrote:
A J-Pole is a 1/2 wave vertical antenna, that sits on TOP of a U
shaped 1/4 wave matching section.
During construction, the 1/2 wave vertical element AND ONE of the 1/4
wave legs of the Transformer are constructed of the same piece of
tubing. Thus the J appearance and name.

RF is invisible to whatever lies below the Horizontal Member, so
whether the mast is grounded or not would have no impact on the
J-Poles performance. However, the shield MUST be grounded for
obvious
reasons.

It is Normal and Proper to RUN the COAX up the center of the mast,
INSIDE the Antenna and EXIT the vertical element at the Horizontal
Member.
If you don't, THEN you will need to stop stray RF that runs along the
coax and/or use a Balun.

When you connect your COAX to the J-Pole:
If it is a MonoBand J-Pole, run the center conductor to the STUB,
leaving the sheild jacket intact up to within about 1/2 inch of the
stub. Then run a wire from the shield horizontal to the horizontal
member and affix this to the vertical.
If it is a Multi-Band J-Pole, the center conductor should be
connected
to the Vertical Element and a wire from the shield runs horizontal
over to the stub.

Although a J-Pole will work with the coax connected either way. On
MonoBand J-Poles, having the center conductor going to the Stub
reduces the noise level slightly. It can make a difference when you
are trying to pull in QRP stations.

Using 3 or 4 1/8th wave wires, like a capacity hat, protruding
outward
on the top of the vertical element will give the same noise reducing
effect.

TTUL
Gary

So, if coax is kept inside the tubing, there is no stray rf and
therefore a choke or balun is not needed?

Are you saying the shield must be grounded to a surge supressor to
prevent lightening stikes?

My ideas was to run the wire inside and even make the coaxle
connections inside the tubing with wire terminals and screws, so as to
keep everything neat and weath proof.

What if you used a non insulated pvc type pipe to connect the stub and
verticle element?






verbositized:

I have been reading alot on different designs and have read
contradictory information on this. Does nayone here have an opinion?

Also, when building a j-pole, could I run the wire inside the tube.
(Regular jacketed copper wire) to the bottom of the tube to a pl
connector? Or would this mess up the impedance?

verbositized:



So, if coax is kept inside the tubing, there is no stray rf and
therefore a choke or balun is not needed?

Some stray RF somewhere, but not enough to worry about regarding the
antenna operation.
However, it is still a good idea to coil a few turns of the coax
before entering the shack.

Are you saying the shield must be grounded to a surge supressor to
prevent lightening stikes?
Not at all, the SHEILD should never go through a supressor.
For proper operation of ANY antenna, the sheild should be grounded.
For lightning protection the sheild should be grounded to an 8 foot
stake OUTSIDE and the center conductor run through a gas bottle also
grounded to the 8 foot stake outside. Actually, every piece of
equipment in the shack should be properly grounded.

My ideas was to run the wire inside and even make the coaxle
connections inside the tubing with wire terminals and screws, so as to
keep everything neat and weath proof.
Sounds good on paper! But I have no idea if it would work, never
tried it. I do know this, with the shield grounded and the antenna
grounded, logically it should make no difference WHERE the shield is
grounded to, but from an RF standpoint, the shield connection to the
vertical must be horizontal with the connection to the driven element.
On Multi-Band J-Poles with single coax feed, we place a horizontal
shorting strap between the connect points of the unfed stub and
vertical element to get the antenna to work properly.
It's been too many years ago that I studied this stuff to remember
why.

What if you used a non insulated pvc type pipe to connect the stub and
verticle element?
Wrong Analogy! Although we use the word Stub, a J-Pole consists of a
1/2 wave vertical element, affixed to one leg of a 1/4 wave U-shaped
matching transformer.
By making the horizontal member from PVC and not contiguous with the
two legs of the U, you would not have a U shaped matching transformer.
FWIW: The U does not have to be vertical, it can be horizontal as is
the upper matching transformer on a Stacked-J and BOTH stubs become
affixed to the vertical elements.

I have seen a unique antenna design that looks like a J-Pole, but the
1/2 wave vertical is insulated from the U-Shaped matching section,
just as a ground plane is insulated from its 1/2 wave vertical.
The feed for this type of antenna was quite hairy to get just right!
If I recall, a brass rod extended up into the vertical about 8 inches
to it's connection point and the lower connection point was similar to
a J-Pole.

TTUL
Gary

wrote
So, if coax is kept inside the tubing, there is no stray rf and
therefore a choke or balun is not needed?

Gary did a good job of answering your questions, but I am reinforcing what
he said.

By design, the J-Pole may allow feedline radiation: None, a little, or a
lot, depending on the users unique configurations of feedline length, design
frequency, and accuracy of matching-stub construction, etc. Therefore an
isolating 1:1 Balun or coils of feedline (choke) at the feedpoint of the
antenna are highly recommended. Routing the coax inside the variable lenth
of the main antenna length to get to the shorting (matching) stub would have
little or no effect on preventing feedline radiation, if your design was
subject to it in the first place.


Are you saying the shield must be grounded to a surge supressor to
prevent lightening stikes?

Not everyone is subject to lightning, and for some it is rare enough that
they choose not to worry about it. But if lightning protection design is
used, it requires shield-grounding. Coax shield (braid, solid, any kind)
must be grounded, and at several points depending on the tower height, mast,
length of feedline, etc. In order for lightning arrestors (more commonly
called SPD or Surge Protection Device) to work properly, the coax shield
must be well grounded *before* it is connected to the arrestor/surge device.
That's another whole subject and we have explained your J-pole doesn't
"need" grounding several times. A copper J-Pole however, is about as
attractive a point for lightning attachment as you could offer. It is also
subject to the same levels of static electricity that any airborne antenna
picks up. Act according to your individual desire for survival there.


My ideas was to run the wire inside and even make the coaxle
connections inside the tubing with wire terminals and screws, so as to
keep everything neat and weath proof.

That would be a really neat and pretty wx-proof design, but a lot of work.
There might be an easier way to wx-proof it, mentioned later.


What if you used a non insulated pvc type pipe to connect the stub and
verticle element?

The cross-connector is a shorting, matching "bar", as Gary warned you
against using the word "stub" if that was going to confuse anyone because it
is not a waveguide or filter or anything else the word stub is normally used
to describe. Therefore it could never be made of an insulating dialectric
such as PVC. You could however hot-dip coat the whole antenna in plastic or
rubber if you wanted to really wx-proof it, and this would eliminate the
difficult inside-assembly of coax in the tubing that your proposed.

One final note: the J-Pole is no miracle antenna. It's has zero gain when
compared to any vertical antenna, and its entire attraction is it "fairly"
easy construction, and very inexpensive construction materials. To get as
*reliable* a vertical antenna for marine use that I required, might have
cost well over $100. At or above that level the vertical antennas of 5/8
wavelength can normally provide gain of 6-10 dbi, and I do not want to get
into what that is compared to as it has been hashed over a million times. I
would leave it at "there will be considerable gain possible in vertical
designs over the J-Pole". You have to be willing to pay for that. Most users
are happy with J-Pole performance so it's record stands pretty well on its
own.

73,
Jack Painter
Virginia Beach, Virginia