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2 meter j-pole

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andrewvickery1

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#1
Ok question, I am wanting to build a 2 meter j-pole and have looked at 100's of designs and have noticed that some have the short leg as the driven element and some have the long as the driven element. I am totaly confused. Please help.
 
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#2
Ok question, I am wanting to build a 2 meter j-pole and have looked at 100's of designs and have noticed that some have the short leg as the driven element and some have the long as the driven element. I am totaly confused. Please help.
Here are plans for one I built. It is dual band but I've found that it works well for my application.

http://www.arrowantennas.com/inst/OSJ146440.pdf
 
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#3
There are some very strange 'facts' in that instruction manual - it suggests using turns of cable to act as a balun - since the antenna is unbalanced to start with, what will you be 'unbalancing'. I also don't understand the reference to a J Pole - as there doesn't seem to be one. Is it not a ¼ wave with parasitic radiators? A J pole is completely different, and is a different design altogether?

The proper J Poles are balanced and the RF applied across the bottom folded section. I suspect that the folded design that looks like a 'J' also looks similar to these stub type ones linked to - but they're not J poles, or the similar Slim Jim.
 
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#4
Ok question, I am wanting to build a 2 meter j-pole and have looked at 100's of designs and have noticed that some have the short leg as the driven element and some have the long as the driven element. I am totaly confused. Please help.
It doesn't matter which element you make as the driven element so do not put a lot of thought into it.
But if you want, here is some lite reading:
https://en.wikipedia.org/wiki/J-pole_antenna
 
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#5
There are some very strange 'facts' in that instruction manual - it suggests using turns of cable to act as a balun - since the antenna is unbalanced to start with, what will you be 'unbalancing'. I also don't understand the reference to a J Pole - as there doesn't seem to be one. Is it not a ¼ wave with parasitic radiators? A J pole is completely different, and is a different design altogether?

The proper J Poles are balanced and the RF applied across the bottom folded section. I suspect that the folded design that looks like a 'J' also looks similar to these stub type ones linked to - but they're not J poles, or the similar Slim Jim.
Granted, it doesn't fit the strict definition of a J-pole is often constructed from copper tubing. It is advertised as one so I took liberties in suggesting it. When I installed mine, I didn't use the balun design as suggested (I suspect the idea is to limit common mode current on the feed line) I also mounted it to a non metallic mast so as to minimize adjacent metal structures interfering with the antenna operation.
 
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#6
We thrashed this to death not so long ago amid all sorts of discussions on why they worked or didn't work. I think in the end enough documentation surfaced to show that a J-pole or it's derivative 'Slim Jim' does not have a stub sticking out of the bottom and you do have to mount it on an insulated pole and away from any surrounding metalwork. It is a 5/8 radiator mounted on quarter-wave matching stub so does not require a balun or braid-breaker in the feed line. The apparent gain over a quarter-wave ground plane is due to the radiation being at a lower angle and so providing better signal level on the ground.

See....

https://en.wikipedia.org/wiki/J-pole_antenna


OK, standby for the flame wars again.......
 

SCPD

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#7
"OK, standby for the flame wars again......"
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(Laffing)
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AndrewV, you might look back a few weeks for this topic under "Amateur Antennas"... for it was most throughly disccuss'd-- by some of us, in a quite scholarly manner- if I do say so myself.... (smiles/laugh.)
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Lackling looking that up, your confusion is perfectly natural...... The "J-Pole" antenna has been a traditional modification of the old Zepp antenna from the early/mid 20th century, but over the years, anything that looks like the letter "J" has usurp'd its name. Unfortunately for this fine antenna, it gets reviews that are all over the place- and usually the most ardent review'rs are technically the least competent to do them.
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Read all you can about the "J" and design yours based on the traditional... The "Copper Cactus's" and their like do work, but are not true "J's."
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............................CF
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#8
I have build no less than five 2 meter J-poles and tried to find this answer many times. There seemed to be no definitive answer with many stating 'it doesn't matter'. I've had excellent results attaching the center conductor to the long (5/8) 'element'. Tip - drill a hole in the top end cap and add an eyelet screw. Hoist it up in a tall tree when you're camping :)
 

SCPD

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#9
Well Sky, it does make a difference, that is, if you are purist. There is a definite design to a true "J" antenna- though I will agree with you-- so many of the variations that go under the "J" name will work, some plus, others minus.
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I just fish'd back over the summer's postings--- here is what some very knowing people had to say about this antenna-- Majoco in particular... if one search's RR forums for
: "Arrow Antenna, J-Pole"
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Personally, from a construction standpoint, I think there are far easier antennas to build that work as well or better than the "J"--- but that's me...
............ although I will throw out on Sage's observation that there are no commercial versions used by industry.... and for a good reason.
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..................CF :)
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#10
Well Sky, it does make a difference, that is, if you are purist. There is a definite design to a true "J" antenna- though I will agree with you-- so many of the variations that go under the "J" name will work, some plus, others minus.
.
I just fish'd back over the summer's postings--- here is what some very knowing people had to say about this antenna-- Majoco in particular... if one search's RR forums for
: "Arrow Antenna, J-Pole"
.
Personally, from a construction standpoint, I think there are far easier antennas to build that work as well or better than the "J"--- but that's me...
............ although I will throw out on Sage's observation that there are no commercial versions used by industry.... and for a good reason.
.
.
..................CF :)
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Back in the early 70's Comco manufactured and sold a J pole antenna, they sold them with their line of VHF-AM base stations used as airband Unicom stations. I remember expressing surprise when one showed up in the shop. It looked like a homebrew project with the elements made from 1/2 EMT with a sort of clamp assembly that held it together.
 
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#11
I'm sorry, but this is making me laugh now - an antenna that looks like a J shape is a J-Pole? Are you serious. The design of a J-Pole is very specific, and the design of other antennas is even based on variations to it. Call it whatever you like, but if it doesn't conform to the design, it's not a J-Pole. There is no argument that makes a dog out of a cat, even if they have four legs and bite!
 
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#13
"A rose by any other name would smell as sweet" . **

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....................Romeo and Juliet,

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. ah, poor sweet Romeo.... :)
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________________________________________
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** maybe not with "J" Poles......... CF
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#14
You really believe that if you stick a Jaguar label on a Ford, because it looks like a Jaguar, it IS a Jaguar?

We are dealing with a technical subject, and antennas use physics, and were designed and frequently evolve, using sound science to explain how they work. If, to your untrained, inexperienced and unsupported viewpoint, you believe some of these antennas are what you believe them to be - that is fine. It's OK to be wrong, but people come here for factual answers, not humbug opinion. For a design to be described as a J-Pole, then it has to follow the appearance, mode of operation and the science behind the design. Looking like a J does not make it a J-pole. A dipole made from wire is still a dipole, even if it is very big. You could then say it is a long wire antenna, and it does have some long wires, but it is a dipole!
 
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#15
Oh, this could launch a very interesting debate into psycholinguistics- but far from me to take it there.... :)
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No one is saying that by changing the name of something is to change the character of it. Just as Romeo said- 'a rose by any other name would smell as sweet"- or in the case of a "J-Pole" antenna- it will be as good or rotten as its appearence --its smell if you wish-- not its name. You can call it anything- its what it looks like, what it does- what it smells like- that determines what it is. A word is just a convenient way of conveying a concept from one person to another.
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We can debate if 'you conrol the language you control the mind'- a concept of George Orwell who said language makes humans easy to control—'control their language and you control the people.'
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On the other hand, languages evolve to suit the ideas and needs that are most crucial to the lives of their speakers... thus if you don't have a single word for the concept, then languages find a way to say what we need to say; if we don't have a word for it, we can describe it in a sentence or a phrase. You may control the words, but you cannot what is behind their meanings.
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A "J-Pole" is a "J-Pole"- it looks like a "J"-- (remember it was once a "Zepp")-- You can call it a whatever you like; if performs like an Angel, then call it the 'Angelic J"... if it doesn't, call it the "Crappy J"... people will catch on quickly and know the meaning- and in time the language will evolve to something like the "Angel J" and or the "Crap J"-- the ham world knows the difference already- now they have the words ..... :)
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............................. CF
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______________________________________________________________
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(I'm a big fan or Orwell.... and can "New Speak" with the best of of them.... :) )
 
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#18
Aaaah...

'control their language and you control the people.'

Now we are back to the dumbing down of the English langauge......

....or the push in primary education in NZ to get all the kids to learn the Maori language, not just the Maori kids but all of them. On a more sensible note, an item on last night's TV news, a primary school in Auckland has classes in Mandarin - certainly no shortage of fluent speakers already. :)
 
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