Talk:J-pole antenna

Official antenna of Jamaica?!?

Oh come on. The reference doesn't check out and why would a country have an official antenna. Crcwiki (talk) 22:30, 19 November 2015 (UTC)

Same reason Alaska, Arizona, Utah, Indiana, Kentucky, Pennsylvania, West Virginia, Tennessee, and Texas all have official State guns. — Preceding unsigned comment added by 71.210.235.219 (talk) 04:05, 8 May 2022 (UTC)

Updates by Crcwiki (talk) 15:18, 2 October 2015 (UTC)

I've incorporated many of the comments below and added a great many references I found after extensive research. There is always room for improvement. For now the basics of the j-pole antenna are well documented. Hopefully it will help dispel some of the myths in the j-pole community such as the SlimJim having a gain over the regular J, masts don't conduct current and other fictitious and misleading nonsense. There are quite a few manufacturers who make these claims leading customers astray. This fact emphasizes the importance of this article as an educational tool to combat the nonsense and help customers spot and report False_advertising. Anyone bringing new material to this article needs to have rock-solid reference material to back it up. Crcwiki (talk) 15:18, 2 October 2015 (UTC)

Older Talk Comments

Links to sites with erroneous claims such as "Although the antenna is a half wave end fed, it will perform better than a half wave ground plane, due to its lower angle of radiation." will be removed to preserve the technical literacy of Wikipedia. Crcwiki (talk) 19:02, 9 September 2014 (UTC)

This article claims that a Slim JIM and a J-Pole are one and the same. This is simply not true. - AB2MH Ryan 01:14, 8 October 2006 (UTC)

I think the section talking about the quarter wave section isolating the antenna is also incorrect. The quarter wave section is a transmission line, and acts as a transmission line impedance transformer. When I have time, I'll fix this and add a reference. I'd also like to add material about the Super J (with phasing section), but not with the article in its current inaccurate state, --ssd 20:31, 14 July 2007 (UTC)

On doing some research, I found Cebik's pages on this (linked now). He seems to say both that the Slim Jim is a variant of the J-pole, which, in turn, is a varient of the end-fed Zeppelin antenna. --ssd 18:52, 21 July 2007 (UTC)

I have rearranged and clarified this article somewhat. I think this is about as much as you can say about a J-pole without going into construction details or its history. The diagram here is nice; I could add pictures, but the j-pole is large and difficult to photograph clearly. --ssd 22:17, 21 July 2007 (UTC)

The J Pole or Zepp Antenna is a voltage fed antenna that was invented by the Germans (citation needed). It was first used on the Zepplin Ballon Air Ships (citation needed) hence the name Zepp Antenna. It consisted of a quarter wave and a half wave length/s of the same peice of ribbon or open feed line. The first quarter was the matching stub and the half wave section with one side of the feedline removed was the end fed radiator. It was simply left to trail from the air ship at altitude. This Zepp Antenna later became known as a J Pole and or Slim Jim. Indeed - the stub is both an impedence match and a transfomer. Somewhere between the lower end - closed circuit, and the top of the stub - open circuit an exact 50 ohm match can be found to suit 50 ohm unbalanced feed lines. The voltage and current above the feed point, on the stub, have equal and opposite voltage an current and cancel each other out leaving the end fed half wave or dipole to radiate. I have built many of these for friends, clubs and emergency services and have found they can be extended to a five eight or three quarter wave end fed (although they becomes dogs to tune and need to be kept clear of any metal objects - unless, placed near a vertical metal mast in which case they then become directional). They can be stacked for greater gain with two end fed three quarters in phase producing up to 6-7DBd. A phasing stub needs to be inserted betwen radiators to return the voltage and current to phase at the start of each new three quater length.

In any event the main page should be edited to indicate the history and it's origional name ZEPP not J Pole. 73 Tidalenergy 00:16, 8 October 2007 (UTC)

On Aug 4, 2008, I found the Cebik link to be password protected and apparently unusable. - KQ7B Jim —Preceding unsigned comment added by 66.232.82.6 (talk) 01:09, 5 August 2008 (UTC)

The links are not 'broken', the site requires registration now. L. B. Cebik died in April 2008 and because of this, some people thought that the site would be taken down. Users began downloading every article on the site, using massive bandwidth. They decided to require registration so that this would be less likely to happen. There are no plans to take down the site. The registration is free and asks only for very basic info. - KB0SPN —Preceding unsigned comment added by Wyphy (talk • contribs) 18:29, 5 September 2008 (UTC)

..."the registration is free and asks only for very basic info" ... including your email address, which they then use to send you a low bandwidth of directed spam and continue even after your registration expires or is deleted. --ssd (talk) 15:54, 14 April 2013 (UTC)

External links modified

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Feeding without the bottom short

Thanks to Chetvorno for many very good edits, but I think this one is not helpful. The statement that "Using low impedance feedline like 50 ohm coaxial cable usually requires removing the short at the bottom of the stub and connecting the feedline at the bottom." is not correct. Almost all J poles are fed by moving the feed point up from the shorted end till a match is found, even with 50 ohm feed. It is true that the quarter wave line can be fed directly at the bottom with no short, but this had the mechanical difficultly of supporting the short side (in the case of the "copper cactus" version) and even more serious, the only way to adjust the Z at the bottom is to change the Zo of the quarter wave line, which must be the geometric mean of the feed lines Zo (50 ohms typically) and the Z looking into the half wave section, which will be high. It is true that the original Zepp, as shown on the patent was fed via a link at the end, without the short. In those days, 50 ohms was not a standard and the transmitter link output could feed any reasonable low Z, so the exact value didn't matter. If anyone can find a reference to substantiate the removed statement, I would like to see it, but I find it very contrary to my own analysis and experience. There are many thousands of 50 ohm fed J poles in use with the short on the bottom, and I have never seen one without it.

As a substitute for the removed statement, we might add that it is possible to feed the J pole directly without the short as long as the Zo of the line is the G.M. of the two matched impedances. However there is no real advantage in doing so and it is not commonly done. BTW this approach looks very appealing when looking at the J pole on a Smith Chart, but in practice it isn't very useful, in my experience.

JNRSTANLEY (talk) 11:33, 15 May 2021 (UTC)

Citations needed

I see some new sentences with no primary references. This article was previously and painstakingly well referenced. The new unreferenced sentences have been tagged along with the section they are in. The new points are valid and I will help seek primary references. If references are not found in short order, they will be removed. Let's not let this concise wiki article about the J antenna turn into the travesty that is the article on the the dipole antenna. crcwiki (talk) 04:41, 24 May 2021 (UTC)