I've been working on a ladder line J-Pole design for 6m, but have had very
little luck until today. The problem has been critical tuning and narrow SWR
bandwidth. The improvement came today when I implemented an idea I had
concerning the severed piece of wire that "just goes along for the ride" in
the ladder line after cutting the 1/4" gap for the 1/4-wave shorted stub. I
figured that many successful 50 MHz J-Poles are made from copper tubing
because the thicker elements give it good bandwidth. My idea was to make use
of the extra wire and connect it at top and at the gap to the radiator side,
making the half-wave radiator act as a much thicker element. My 2:1
bandwidth went from 300 KHz to 2 MHz.

The resulting antenna design is very straightforward, using the Velocity
Factor of 0.91 for the 1/4-wave stub and 0.95 for the radiator. This
essentially sets the radiator length equal to the standard 468/F dipole
length. If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both the
radiator and the stub, which is appropriate in their open design. So that
pointed me in that direction as far as cutting lengths are concerned. The
only remaining question was the location of the feed tap for 50-ohm cable. I
used alligator clips on the coax to find the best position, and that turned
out to be 4 3/8" up from the shorted bottom end, with the shield going to
the gap side. My rig sees a 1:1 SWR from 50.0 to 51.2 MHz, and it gets to
1.6:1 at 52.1 MHz. With this information, it should be easy to design one
that takes full advantage of the antenna's bandwidth to provide operation
over the widest segment of the 6M band.

My intuition told me that there should be some advantage to using 450-ohm
ladder line compared to 300-ohm twinlead. Maybe this extra bandwidth is it.

73,

Chuck, W6PKP

"Chuck Olson" wrote in message
. ..
I've been working on a ladder line J-Pole design for 6m, but have had very
little luck until today. The problem has been critical tuning and narrow
SWR
bandwidth. The improvement came today when I implemented an idea I had
concerning the severed piece of wire that "just goes along for the ride"
in
the ladder line after cutting the 1/4" gap for the 1/4-wave shorted stub.
I
figured that many successful 50 MHz J-Poles are made from copper tubing
because the thicker elements give it good bandwidth. My idea was to make
use
of the extra wire and connect it at top and at the gap to the radiator
side,
making the half-wave radiator act as a much thicker element. My 2:1
bandwidth went from 300 KHz to 2 MHz.

The resulting antenna design is very straightforward, using the Velocity
Factor of 0.91 for the 1/4-wave stub and 0.95 for the radiator. This
essentially sets the radiator length equal to the standard 468/F dipole
length. If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both the
radiator and the stub, which is appropriate in their open design. So that
pointed me in that direction as far as cutting lengths are concerned. The
only remaining question was the location of the feed tap for 50-ohm cable.
I
used alligator clips on the coax to find the best position, and that
turned
out to be 4 3/8" up from the shorted bottom end, with the shield going to
the gap side. My rig sees a 1:1 SWR from 50.0 to 51.2 MHz, and it gets to
1.6:1 at 52.1 MHz. With this information, it should be easy to design one
that takes full advantage of the antenna's bandwidth to provide operation
over the widest segment of the 6M band.

My intuition told me that there should be some advantage to using 450-ohm
ladder line compared to 300-ohm twinlead. Maybe this extra bandwidth is
it.

73,

Chuck, W6PKP



It looks like I left out the design frequency that resulted in the 2:1 SWR
bandwidth from 49.54 to 51.53 MHz, and that was 51.13 MHz. It looks like
there's an offset of +600 KHz between the frequency used to determine
cutting length and the actual center of SWR bandwidth. But once that's
known, the design can be calculated for precise frequency coverage.

Maybe we should call it a "Fat-Wire J-pole" - - feel free to offer
alternatives - -

73,

Chuck, W6PKP

Have you not just re-invented the 'Slim Jim'??

73
Jeff

"Chuck Olson" wrote in message
. ..
I've been working on a ladder line J-Pole design for 6m, but have had very
little luck until today. The problem has been critical tuning and narrow
SWR
bandwidth. The improvement came today when I implemented an idea I had
concerning the severed piece of wire that "just goes along for the ride"
in
the ladder line after cutting the 1/4" gap for the 1/4-wave shorted stub.
I
figured that many successful 50 MHz J-Poles are made from copper tubing
because the thicker elements give it good bandwidth. My idea was to make
use
of the extra wire and connect it at top and at the gap to the radiator
side,
making the half-wave radiator act as a much thicker element. My 2:1
bandwidth went from 300 KHz to 2 MHz.

The resulting antenna design is very straightforward, using the Velocity
Factor of 0.91 for the 1/4-wave stub and 0.95 for the radiator. This
essentially sets the radiator length equal to the standard 468/F dipole
length. If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both the
radiator and the stub, which is appropriate in their open design. So that
pointed me in that direction as far as cutting lengths are concerned. The
only remaining question was the location of the feed tap for 50-ohm cable.
I
used alligator clips on the coax to find the best position, and that
turned
out to be 4 3/8" up from the shorted bottom end, with the shield going to
the gap side. My rig sees a 1:1 SWR from 50.0 to 51.2 MHz, and it gets to
1.6:1 at 52.1 MHz. With this information, it should be easy to design one
that takes full advantage of the antenna's bandwidth to provide operation
over the widest segment of the 6M band.

My intuition told me that there should be some advantage to using 450-ohm
ladder line compared to 300-ohm twinlead. Maybe this extra bandwidth is
it.

73,

Chuck, W6PKP

Hi, Jeff,

Thanks for the reference to a similar design. The Slim-Jim may perform as
well as the thing that I put together, but my implementation added a
connection from the bottom end of the radiator opposite the gap to the wire
end above the gap. Computer simulation may reveal that both perform
identically despite the difference. In that case, I would suggest leaving
out that bottom connection since it's a little extra work. The Slim-Jim
never came up in my search effort to find a good J-Pole design, so I'm glad
to see this promising area of further search.

73

Chuck, W6PKP

"Jeff" wrote in message ...
Have you not just re-invented the 'Slim Jim'??

73
Jeff

"Chuck Olson" wrote in message
. ..
I've been working on a ladder line J-Pole design for 6m, but have had
very
little luck until today. The problem has been critical tuning and narrow
SWR
bandwidth. The improvement came today when I implemented an idea I had
concerning the severed piece of wire that "just goes along for the ride"
in
the ladder line after cutting the 1/4" gap for the 1/4-wave shorted
stub.
I
figured that many successful 50 MHz J-Poles are made from copper tubing
because the thicker elements give it good bandwidth. My idea was to make
use
of the extra wire and connect it at top and at the gap to the radiator
side,
making the half-wave radiator act as a much thicker element. My 2:1
bandwidth went from 300 KHz to 2 MHz.

The resulting antenna design is very straightforward, using the Velocity
Factor of 0.91 for the 1/4-wave stub and 0.95 for the radiator. This
essentially sets the radiator length equal to the standard 468/F dipole
length. If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub, which is appropriate in their open design. So
that
pointed me in that direction as far as cutting lengths are concerned.
The
only remaining question was the location of the feed tap for 50-ohm
cable.
I
used alligator clips on the coax to find the best position, and that
turned
out to be 4 3/8" up from the shorted bottom end, with the shield going
to
the gap side. My rig sees a 1:1 SWR from 50.0 to 51.2 MHz, and it gets
to
1.6:1 at 52.1 MHz. With this information, it should be easy to design
one
that takes full advantage of the antenna's bandwidth to provide
operation
over the widest segment of the 6M band.

My intuition told me that there should be some advantage to using
450-ohm
ladder line compared to 300-ohm twinlead. Maybe this extra bandwidth is
it.

73,

Chuck, W6PKP

Today I clipped out the connection I had made at the bottom of the radiator,
and the SWR bandwidth remained 2MHz as is was with the connection. The group
of SWR measurements moved up an average of 150 KHz from my readings with the
connection, but otherwise the performance of the "Slim Jim" configuration is
identical. The length of the gap may now serve as a tuning mechanism, which
wasn't a feature with the bottom connection, and the archives show some
builders made good use of that facility. Thanks for spotting the similarity,
Jeff. My 6M antenna will no doubt be better for it.

73,

Chuck

"Jeff" wrote in message ...
Have you not just re-invented the 'Slim Jim'??

73
Jeff

"Chuck Olson" wrote in message
. ..
I've been working on a ladder line J-Pole design for 6m, but have had
very
little luck until today. The problem has been critical tuning and narrow
SWR
bandwidth. The improvement came today when I implemented an idea I had
concerning the severed piece of wire that "just goes along for the ride"
in
the ladder line after cutting the 1/4" gap for the 1/4-wave shorted
stub.
I
figured that many successful 50 MHz J-Poles are made from copper tubing
because the thicker elements give it good bandwidth. My idea was to make
use
of the extra wire and connect it at top and at the gap to the radiator
side,
making the half-wave radiator act as a much thicker element. My 2:1
bandwidth went from 300 KHz to 2 MHz.

The resulting antenna design is very straightforward, using the Velocity
Factor of 0.91 for the 1/4-wave stub and 0.95 for the radiator. This
essentially sets the radiator length equal to the standard 468/F dipole
length. If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub, which is appropriate in their open design. So
that
pointed me in that direction as far as cutting lengths are concerned.
The
only remaining question was the location of the feed tap for 50-ohm
cable.
I
used alligator clips on the coax to find the best position, and that
turned
out to be 4 3/8" up from the shorted bottom end, with the shield going
to
the gap side. My rig sees a 1:1 SWR from 50.0 to 51.2 MHz, and it gets
to
1.6:1 at 52.1 MHz. With this information, it should be easy to design
one
that takes full advantage of the antenna's bandwidth to provide
operation
over the widest segment of the 6M band.

My intuition told me that there should be some advantage to using
450-ohm
ladder line compared to 300-ohm twinlead. Maybe this extra bandwidth is
it.

73,

Chuck, W6PKP

"Chuck Olson" wrote in message
...
Today I clipped out the connection I had made at the bottom of the
radiator,
and the SWR bandwidth remained 2MHz as is was with the connection. The
group
of SWR measurements moved up an average of 150 KHz from my readings with
the
connection, but otherwise the performance of the "Slim Jim" configuration
is
identical. The length of the gap may now serve as a tuning mechanism,
which
wasn't a feature with the bottom connection, and the archives show some
builders made good use of that facility. Thanks for spotting the
similarity,
Jeff. My 6M antenna will no doubt be better for it.
73, Chuck


Chuck,
I searched on Slim-Jim. Let me see if I understand correctly.
Slim-Jim is a twin-lead or ladder-line type J antenna with the *top* of the
half-wave 9dual conductor) radiator ends connected.
Yours has the bottom of the 1/2 wave ends connected.
Am I to understand that the Slim-Jim configuration and yours have very
similar SWR BW?
This is good to know.

Then I'd like clarification on your comment:
"... If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both the
radiator and the stub,..."

Can you be more specific about this. What is the electrical length of the
stub for said analysis? I like that design, though there is controversy
about it.

73, Steve, K9DCi

"Steve N." wrote in message
...

"Chuck Olson" wrote in message
...
Today I clipped out the connection I had made at the bottom of the
radiator,
and the SWR bandwidth remained 2MHz as is was with the connection. The
group
of SWR measurements moved up an average of 150 KHz from my readings with
the
connection, but otherwise the performance of the "Slim Jim"
configuration
is
identical. The length of the gap may now serve as a tuning mechanism,
which
wasn't a feature with the bottom connection, and the archives show some
builders made good use of that facility. Thanks for spotting the
similarity,
Jeff. My 6M antenna will no doubt be better for it.
73, Chuck


Chuck,
I searched on Slim-Jim. Let me see if I understand correctly.
Slim-Jim is a twin-lead or ladder-line type J antenna with the *top* of
the
half-wave (dual conductor) radiator ends connected.
Yours has the bottom of the 1/2 wave ends connected.

Yes, I conncted both top and bottom of the radiator to the previously
floating wire, and when I removed the bottom connection, the SWR bandwidth
remained as before, so the bottom connection does not appear to be
necessary. The top connection is very easy, and evidently that's all you
need, so no doubt about it - - it becomes a Slim-Jim.

Am I to understand that the Slim-Jim configuration and yours have very
similar SWR BW?

Yes.

This is good to know.

Then I'd like clarification on your comment:
"... If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub,..."

Can you be more specific about this. What is the electrical length of the
stub for said analysis? I like that design, though there is controversy
about it.

I'm old fashioned, so I use an HP17BII calculator which has a "solve"
function, and with the formula, LIN = 11811 / F(MHZ) / 4 x VF, given any two
of LIN, FMHZ, and FV, I can obtain the third for a 1/4 wave stub.

We find on the Arrow site http://www.arrowantennas.com/j-pole.html the
longest element for operation at 146 MHz is 57.5", and the shorter element
that makes the 1/4-wave stub is 19.25". With FMHZ = 146 and LIN = 19.25" we
solve for VF of that shorter element and get 0.95 (which refers to the free
space 1/4-wave as 1.00). Subtracting the 19.25 from 57.5 we get the radiator
length of 38.25". Since that is a 1/2-wave length, we divide by 2 so we can
use the 1/4-wave formula, and solving for VF we again get 0.95. I hope this
helps.


73, Steve, K9DCi



Best regards,

Chuck, W6PKP

On Tue, 13 Jun 2006 14:27:14 -0700, "Chuck Olson"
wrote:


"Steve N." wrote in message
...

"Chuck Olson" wrote in message
...
Today I clipped out the connection I had made at the bottom of the
radiator,
and the SWR bandwidth remained 2MHz as is was with the connection. The
group
of SWR measurements moved up an average of 150 KHz from my readings with
the
connection, but otherwise the performance of the "Slim Jim"
configuration
is
identical. The length of the gap may now serve as a tuning mechanism,
which
wasn't a feature with the bottom connection, and the archives show some
builders made good use of that facility. Thanks for spotting the
similarity,
Jeff. My 6M antenna will no doubt be better for it.
73, Chuck


Chuck,
I searched on Slim-Jim. Let me see if I understand correctly.
Slim-Jim is a twin-lead or ladder-line type J antenna with the *top* of
the
half-wave (dual conductor) radiator ends connected.
Yours has the bottom of the 1/2 wave ends connected.

Yes, I conncted both top and bottom of the radiator to the previously
floating wire, and when I removed the bottom connection, the SWR bandwidth
remained as before, so the bottom connection does not appear to be
necessary. The top connection is very easy, and evidently that's all you
need, so no doubt about it - - it becomes a Slim-Jim.

Am I to understand that the Slim-Jim configuration and yours have very
similar SWR BW?

Yes.

This is good to know.

Then I'd like clarification on your comment:
"... If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub,..."

Can you be more specific about this. What is the electrical length of the
stub for said analysis? I like that design, though there is controversy
about it.

I'm old fashioned, so I use an HP17BII calculator which has a "solve"
function, and with the formula, LIN = 11811 / F(MHZ) / 4 x VF, given any two
of LIN, FMHZ, and FV, I can obtain the third for a 1/4 wave stub.

We find on the Arrow site http://www.arrowantennas.com/j-pole.html the
longest element for operation at 146 MHz is 57.5", and the shorter element
that makes the 1/4-wave stub is 19.25". With FMHZ = 146 and LIN = 19.25" we
solve for VF of that shorter element and get 0.95 (which refers to the free
space 1/4-wave as 1.00). Subtracting the 19.25 from 57.5 we get the radiator
length of 38.25". Since that is a 1/2-wave length, we divide by 2 so we can
use the 1/4-wave formula, and solving for VF we again get 0.95. I hope this
helps.


73, Steve, K9DCi



Best regards,

Chuck, W6PKP


My 2-meter ladderline j-pole is connected at the bottom of the
apparatus only, forming the hook of the so-called "J". Yours is
connected at the very top and very bottom, forming kind of a double
"J"?

bob
k5qwg

"Chuck Olson" wrote in message
. ..

"Steve N." wrote in message
...

[...snip...]

Then I'd like clarification on your comment:
"... If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub,..."

Can you be more specific about this. What is the electrical length of
the
stub for said analysis? I like that design, though there is controversy
about it.

I'm old fashioned, so I use an HP17BII calculator which has a "solve"
function, and with the formula, LIN = 11811 / F(MHZ) / 4 x VF, given any
two
of LIN, FMHZ, and FV, I can obtain the third for a 1/4 wave stub.

We find on the Arrow site http://www.arrowantennas.com/j-pole.html the
longest element for operation at 146 MHz is 57.5", and the shorter
element
that makes the 1/4-wave stub is 19.25". With FMHZ = 146 and LIN = 19.25"
we
solve for VF of that shorter element and get 0.95 (which refers to the
free
space 1/4-wave as 1.00). Subtracting the 19.25 from 57.5 we get the
radiator
length of 38.25". Since that is a 1/2-wave length, we divide by 2 so we
can
use the 1/4-wave formula, and solving for VF we again get 0.95. I hope
this
helps.



OK, then I believe you are assuming the short section is exactly 1/4 wave?
That's what I was after. I'm not convinced this is the case, but it is a
complex arrangement...matching 50 to an end fed half-wave.

73, Steve, K9DCI

"Bob Miller" wrote in message
...
On Tue, 13 Jun 2006 14:27:14 -0700, "Chuck Olson"
wrote:


"Steve N." wrote in message
...

"Chuck Olson" wrote in message
...
Today I clipped out the connection I had made at the bottom of the
radiator,
and the SWR bandwidth remained 2MHz as is was with the connection.
The
group
of SWR measurements moved up an average of 150 KHz from my readings
with
the
connection, but otherwise the performance of the "Slim Jim"
configuration
is
identical. The length of the gap may now serve as a tuning mechanism,
which
wasn't a feature with the bottom connection, and the archives show
some
builders made good use of that facility. Thanks for spotting the
similarity,
Jeff. My 6M antenna will no doubt be better for it.
73, Chuck


Chuck,
I searched on Slim-Jim. Let me see if I understand correctly.
Slim-Jim is a twin-lead or ladder-line type J antenna with the *top* of
the
half-wave (dual conductor) radiator ends connected.
Yours has the bottom of the 1/2 wave ends connected.

Yes, I conncted both top and bottom of the radiator to the previously
floating wire, and when I removed the bottom connection, the SWR
bandwidth
remained as before, so the bottom connection does not appear to be
necessary. The top connection is very easy, and evidently that's all you
need, so no doubt about it - - it becomes a Slim-Jim.

Am I to understand that the Slim-Jim configuration and yours have very
similar SWR BW?

Yes.

This is good to know.

Then I'd like clarification on your comment:
"... If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub,..."

Can you be more specific about this. What is the electrical length of
the
stub for said analysis? I like that design, though there is
controversy
about it.

I'm old fashioned, so I use an HP17BII calculator which has a "solve"
function, and with the formula, LIN = 11811 / F(MHZ) / 4 x VF, given any
two
of LIN, FMHZ, and FV, I can obtain the third for a 1/4 wave stub.

We find on the Arrow site http://www.arrowantennas.com/j-pole.html the
longest element for operation at 146 MHz is 57.5", and the shorter
element
that makes the 1/4-wave stub is 19.25". With FMHZ = 146 and LIN = 19.25"
we
solve for VF of that shorter element and get 0.95 (which refers to the
free
space 1/4-wave as 1.00). Subtracting the 19.25 from 57.5 we get the
radiator
length of 38.25". Since that is a 1/2-wave length, we divide by 2 so we
can
use the 1/4-wave formula, and solving for VF we again get 0.95. I hope
this
helps.


73, Steve, K9DCi



Best regards,

Chuck, W6PKP


My 2-meter ladderline j-pole is connected at the bottom of the
apparatus only, forming the hook of the so-called "J". Yours is
connected at the very top and very bottom, forming kind of a double
"J"?

bob
k5qwg

Yea, there's another double back at the top if you connect it there. And
it is easier at th etop with twin-lead. ... simply makes that upper
half-wave a single parallel sonductor, instead of one with a floating
conductor next to it. I wouldn't be surprised if you couldn't widen the
bandwidth a bit by playing with the length of that floating wire. However,
connecting it at either the top and/or botton seems to make a big
improvement very easily. I'd have to think a bit as to why the floating
wire reduces the bandwidth...or the converse if the wider bandth is simply a
case of a "thicker" condustor simulated by the parallel wires.

73, Steve, k9DCI