Does a j pole need grounding and/or a balun?
 

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?

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?

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

Jack Painter wrote:
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

What type of verticle are you talking about, like a ground plane? Would
a ground plane be a better antenna for 2meters?

On 8 Jan 2005 18:16:02 -0800, wrote:

What type of verticle are you talking about, like a ground plane? Would
a ground plane be a better antenna for 2meters?

A ¼-wave groundplane, a ½-wave dipole, a J-Pole or 5/8-wave ground
plane in most typical installations according to NEC analysis will not
vary more than a dB at best.

Remember a receiving station can hardly detect a dB difference.

Danny, K6MHE

wrote
Jack Painter wrote:
wrote
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

What type of verticle are you talking about, like a ground plane? Would
a ground plane be a better antenna for 2meters?


Yes/Yes, and there are a number of verticals with referenced gain far in
excess of the more or less unity-gain J-Pole. The specific ones I mentioned
are Marine. Like a vertical-dipole the J-Pole is a "complete" antenna and
requires no radials, I doubt that it could even benefit from them. And the
gain is referring to transmit, not receive, as all verticals are pretty
equal in reception (and it's not always pretty ;-)

What is your target for 2 meters? General area coverage or specific
directional? Need to null out signals or interference from specific
directions? Look at aYagi. J-Poles are not for anything special, just good
general coverage at about $10 in parts. At that job they have become very
popular antennas!

73,
Jack Painter
Virginia Beach, Virginia

verbositized:


What type of verticle are you talking about, like a ground plane? Would
a ground plane be a better antenna for 2meters?

Check out my Stacked-J for 2 meters. It is a J-Pole on top of a
J-Pole.
I don't know the difference in gain, but in comparison to a regular
J-Pole on the same mast, the Stacked-J outperformed it hands down.

From St. Louis County, MO I could reach both UMR (Rolla) and UofC
(Columbia) repeaters on the Stacked-J at 30 watts, a little noisy on
their end, but I was clear. On a single J-Pole I could not bring up
their repeaters even at 50 watts.

The Stacked-J can be found at http://archimedes.galilei.com/raiar
It's under Antenna's.

TTUL
Gary

Dan Richardson wrote:
On 8 Jan 2005 18:16:02 -0800, wrote:

What type of verticle are you talking about, like a ground plane?
Would
a ground plane be a better antenna for 2meters?

A =BC-wave groundplane, a =BD-wave dipole, a J-Pole or 5/8-wave ground
plane in most typical installations according to NEC analysis will
not
vary more than a dB at best.

Remember a receiving station can hardly detect a dB difference.

Danny, K6MHE

So, about any omni is as good as another? Thanks for yoru info. Are
there any other advantages to building one or another?

Why does this guy say his j po;e have 3 db gain over a ground plane?
http://cgi.ebay.com/ws/eBayISAPI.dll...30959 97&rd=1

On 10 Jan 2005 05:42:53 -0800, wrote:

Why does this guy say his j po;e have 3 db gain over a ground plane?
http://cgi.ebay.com/ws/eBayISAPI.dll...30959 97&rd=1

Why don't you ask him?

wrote:
So, about any omni is as good as another?

Nope, he didn't say that. Stacked phased vertical elements,
as exist in repeater antennas, can offer a tremendous amount
of gain over a 1/4WL ground plane. I have an old Comet 2x4MAX
and the gain over a 1/4WL ground plane is amazing.

The Diamond NR22L for 2m, is 97" long and is two elements of
5/8WL each and thus will have about 3 dB gain over a 1/4WL
ground plane, about the same as an Extended Double Zepp.
--
73, Cecil http://www.qsl.net/w5dxp


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wrote:
Why does this guy say his j pole have 3 db gain over a ground plane?
http://cgi.ebay.com/ws/eBayISAPI.dll...30959 97&rd=1

He might be making the J-Pole one-wavelength long which would
indeed result in about 3 dB of gain but at a relatively useless
take-off-angle.
--
73, Cecil http://www.qsl.net/w5dxp


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http://cgi.ebay.com/ws/eBayISAPI.dll...30959 97&rd=1

He might be making the J-Pole one-wavelength long which would
indeed result in about 3 dB of gain but at a relatively useless
take-off-angle.

I suspect that he's comparing a standard half-wave-radiator J-pole to
a typical "ground plane" antenna (a quarter-wave monopole, with one
set of quarter-wave radials, possibly tilted downwards for an
impedance match).

The latter sort of antenna falls somewhat short of behaving like
a true infinite-ground-plane antenna, as the radials are neither
horizontal nor infinite in extent. If I recall correctly, the
radiation pattern will be tilted upwards from the horizon by
a significant amount.

The J-pole will be close to 0 dBd, while the "ground plane" will
probably fall a few dB short of that figure out at the horizon.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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