Howdy:
In a j-pole the 1/4 wave element, and the bottom 1/4 of the 3/4
element should act as a transmission line, right? So... shouldn't these
elements be as very close to each other to cancel one another out, closer
than what I see on most j-poles? Or is this space have something to do
with the impedance of the antenna?

--
SeeYaa Harbin Osteen KG6URO

This is YOUR futu
http://halturnershow.com/aztlan_caps.wmv
http://media.putfile.com/La-Gran-Marcha
The Mexican Solution:
http://www.centerforsecuritypolicy.o...s&code=06-D_18

-

On Thu, 4 May 2006 17:20:24 -0700, "Harbin"
wrote:

Howdy:
In a j-pole the 1/4 wave element, and the bottom 1/4 of the 3/4
element should act as a transmission line, right? So... shouldn't these
elements be as very close to each other to cancel one another out, closer
than what I see on most j-poles? Or is this space have something to do
with the impedance of the antenna?

Remember you are using wavelengths as your measurement. On 160-meters
6-foot separation would be okay.

Danny



In my many years I have come to a conclusion that one
useless man is a shame, two is a law firm, and three
or more is a congress. - John Adams

email: k6mheatarrldotnet
http://www.k6mhe.com/

Hello Harbin

The bottom of the J-Pole antenna is a 1/4 wave length to transform the high impedance of the 1/2 wave length above into a lower impedance (close to 50 ohms). The impedance of that 1/4WL sould be Z = SQUARE ( Z coax X Z antenna) .... in that case Z antenna is the impedance of the 1/2 WL (usually several hundreds ohms)
That's why the space between elements as well as there diameter is important.

You certainly know the Topfkreis ... which is the same antenna ... 1/2 WL + 1/4 WL ... but with another technical realisation.

Hoping it helps.

Regards

Jean-Marc
F4DRH
www.barbaxoops.com




"Harbin" a écrit dans le message de news: ...
Howdy:
In a j-pole the 1/4 wave element, and the bottom 1/4 of the 3/4
element should act as a transmission line, right? So... shouldn't these
elements be as very close to each other to cancel one another out, closer
than what I see on most j-poles? Or is this space have something to do
with the impedance of the antenna?

--
SeeYaa Harbin Osteen KG6URO

This is YOUR futu
http://halturnershow.com/aztlan_caps.wmv
http://media.putfile.com/La-Gran-Marcha
The Mexican Solution:
http://www.centerforsecuritypolicy.o...s&code=06-D_18

-

F4DRH wrote:
Hello Harbin

The bottom of the J-Pole antenna is a 1/4 wave length to transform the
high impedance of the 1/2 wave length above into a lower impedance
(close to 50 ohms). The impedance of that 1/4WL sould be Z = SQUARE ( Z
coax X Z antenna) .... in that case Z antenna is the impedance of the
1/2 WL (usually several hundreds ohms)
That's why the space between elements as well as there diameter is
important.

You certainly know the Topfkreis ... which is the same antenna ... 1/2
WL + 1/4 WL ... but with another technical realisation.

Hoping it helps.

Regards

Jean-Marc
F4DRH

Jean-Marc

Thanks for mentioning the Topfkreis. It seems like it should work much
better, and is so obvious once you see it. I will have to make one.

tom
K0TAR

On Sun, 07 May 2006 20:05:28 -0500, Tom Ring
wrote:



Thanks for mentioning the Topfkreis. It seems like it should work much
better, and is so obvious once you see it. I will have to make one.

tom
K0TAR


OK, I did a search, unsuccessfully, on Topfkreis. What is it and
where do I find it?

thanks
Buck

--
73 for now
Buck
N4PGW

On Mon, 08 May 2006 02:55:04 GMT,
wrote:
[snip]

If it's what I think it is the design is a coaxial feed section with
a 1/2wl radiator. The difference being a coax fed rather than a
balanced line feed. In either case it relies on an unterminated 1/4wl
section reflecting a high impedence to match the end impedence of
a 1/2wl section. That being something in the range of 3000-5000
ohms (at resonance).

There is also a third way to implement. use a lumped tuned circuit
and tap the coax up from the bottom for match. The tuned circuit is
parallel resonant with the 1/2wl section attached to the top. I've
built this for use with my VHF HT and is about 38" for the radiator
and the coil at the bottom looks like a baseloading coil. Works
way better than a rubber duck but at 40" long overall it's big.


Here's another approach you might be interested in.

http://k6mhe.com/files/ssfm.pdf

73, Danny

In my many years I have come to a conclusion that one
useless man is a shame, two is a law firm, and three
or more is a congress. - John Adams

email: k6mheatarrldotnet
http://www.k6mhe.com/

writes:
If it's what I think it is the design is a coaxial feed section with
a 1/2wl radiator. The difference being a coax fed rather than a
balanced line feed. In either case it relies on an unterminated 1/4wl
section reflecting a high impedence to match the end impedence of
a 1/2wl section. That being something in the range of 3000-5000
ohms (at resonance).

Here's a very simple end fed vertical dipole:

http://www.la2t.org/otfgallery/album...plukk/1002.jpg

http://f3wm.free.fr/radio/pocket.html

It's simply a piece of coax. The braid is stripped off the last 1/4
wavelength. Another 1/4 wavelength from the end, there is a choke to isolate
a 1/4 wavelength of braid from the rest of the cable. Presto, dipole!

Support it with a fishing rod, hang it from a tree, whatever.

73 de LA4RT Jon

In article ,
Tom Ring wrote:

OK, I did a search, unsuccessfully, on Topfkreis. What is it and
where do I find it?

I found these. Not in english, but it hardly matters.

http://membres.lycos.fr/arrad38/bido.../topfkreis.htm
http://f5jtz.club.fr/pjacquet/topkreis.htm

Also try Googling for "sperrtopf" or "sperrtof". Same basic idea...
a J-pole-like extended Zepp in which the matching section is a coaxial
sleeve.

--
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
boycott any company which has the gall to send me such ads!

Harbin,
You seem to understand the "J-Antenna". What you really seem to be asking is how far apart is "too far" for a balanced transmission line. That's a question I can't answer and I'm sure others can, but , in the common custom of adding obtuse references which sort of seem to be relevant... what about that old one wire transmission like the "G-Line"? [no joke]

73, Steve, K9DCI


"Harbin" wrote in message ...
Howdy:
In a j-pole the 1/4 wave element, and the bottom 1/4 of the 3/4
element should act as a transmission line, right? So... shouldn't these
elements be as very close to each other to cancel one another out, closer
than what I see on most j-poles? Or is this space have something to do
with the impedance of the antenna?

--
SeeYaa Harbin Osteen KG6URO

This is YOUR futu
http://halturnershow.com/aztlan_caps.wmv
http://media.putfile.com/La-Gran-Marcha
The Mexican Solution:
http://www.centerforsecuritypolicy.o...s&code=06-D_18

-

OOPS! Jon,
IF it is "end-fed" is isn't a "di-pole". It is just a half wave. I
guess it is technically a monopole.
73, Steve, K9DCI

"Jon KÃ¥re Hellan" wrote in message
...

Here's a very simple end fed vertical dipole:

http://www.la2t.org/otfgallery/album...plukk/1002.jpg

http://f3wm.free.fr/radio/pocket.html

It's simply a piece of coax. The braid is stripped off the last 1/4
wavelength. Another 1/4 wavelength from the end, there is a choke to
isolate
a 1/4 wavelength of braid from the rest of the cable. Presto, dipole!

Support it with a fishing rod, hang it from a tree, whatever.

73 de LA4RT Jon