nd5y
Member
All I'm saying is if it wasn't a poor design you would see them in commercial installations.
Collinear, 1/4 wave GP, or J Pole (arrow)
- Thread starter SpugEddy
- Start date
- Status
NC1
Member
I thought the issue was grounding vs accepted practice not to ground, but OK.
These are not rated for high power, so it would be logical to not see them in commercial installations, then again I have never looked for one either.
We are not dealing with a commercial installation here, so the point is irrelevant for the discussion.
I think a lot of the problems come up from poor installation. Grounding it and having any metal within 2 feet of it will end up with undesired operation. I tend to believe it's not a poor design as much as it is a user error in the execution of the build, and/or installation.
I have seen the best made antennas work like crap because the person who assembled and installed it was clueless, and ran some garbage made cable to it as well.
A stock J-pole will be influenced by grounding or attaching to a metal support pipe. etc. This is because these antennas have lots of common mode currents riding on the coax because of poor decoupling. If you decouple the J-pole with proper use of ferrite, then whatever is below the ferrite has little influence on the antenna.
I've done this and it works on J-poles and many other antennas that have feedline decoupling problems. This is not something I made up, its common knowledge. Most likely the so called designer of the antenna was not up on common mode currents and how to address them.
prcguy
I've done this and it works on J-poles and many other antennas that have feedline decoupling problems. This is not something I made up, its common knowledge. Most likely the so called designer of the antenna was not up on common mode currents and how to address them.
prcguy
NC1
Member
Well, there is that, or somebody could use it as it is designed and just not ground the dang thing.
I hit repeaters 30+ miles away while pushing only 5W from an HT without an issue, using my 2 meter SlimJim. And yes, it has no ground. Amazing, don't you think?
I am not the only one who gets these kind of results, it's actually quite common.
Ferrite or no ferrite, it's not supposed to be grounded.
majoco
Stirrer
Fred Judd G2BCX.
Here's a copy straight out the "Out of Thin Air" booklet , my copy dated 1981.
Original Slim Jim Antenna Article by F.C. Judd - The 2BCX Slim Jim Antenna - G2BCX
You will note in the text that he says that tuning should be done using the full length of the coax cable that will be used in the final installation.
I have been following the discussion on these antennas -and several things strike me. First off, both the ‘J’ design and the “Slim Jim” are not Beginner’s Antennas-- especially! the later. I just read G2BCX’s article; I understand the theory behind this antenna; at the same time I can also see that building one by a neophyte is fraught with pit falls. Mechanically it is an awkward design. Constructing it to be stable enuff for long term out-of-doors would be challenging, there is no provision to ground it, the feed points are vague, and the use of twinlead feedlines makes me cringe (tho coax can be used) - these are among the detractors I found.
.
ND5Y sum’d it up: ….
“All I'm saying is if it wasn't a poor design you would see them in commercial installations”
.
In fairness to G2BCX, I sure his design works well for him, but there is a vast difference between the lab and the field… which brings me to point number Two--
.
SpugEddy, I am going to step you aside - for after all you were the one asking the original questions. I’m telling you that these types of antennas may be in your future, but steer clear of them for now. Aside from the obvious quarter-wave ground plane, here are a few of my suggestions if you still want to build-
.
Try your hand at that coaxial collinear vertical- but do it by the book- no substitutions of coax’s, etc….. or try some of the other phased section collinears… the books are full of them. The nice about these- you can assemble them in fiberglass or PVC pipes to make them weather proof...and they can be grounded
One of my favorites- the fold’d dipole- they are mechanically as tough as bricks. You can stack them in phase for additional gain, if you wish, they are easy to build and tune….. And going back to the commercial standard analogy- look at any 2-way tower- they are the antennas of choice.
.
Personally, I like the design of the Ringo Ranger.. ..not only for their simplicity of design, but ease of tuning- not to mention their inherent static suppression- everything is at DC ground. In the field we use similar designs all the time on 400-420MHz. If you feel so inclined, they are easy to duplicate.
.
What I am trying to get across is to avoid the anecdotal stories of how great an antenna is to one particular person as compared to something else. Antennas are one highly charged subject for hams… so approach them like a scientist,--- for remember, you can get a brine soaked piece of string to radiate RF- and some might laud it to the heavens as the best thing since sliced bread.
.
…………….CF
.
.
If I get a few moments in the next couple of weeks I might put together a UHF “Slim Jim” design and run it thru a few lab tests of my own- stay tuned…….
.
ND5Y sum’d it up: ….
“All I'm saying is if it wasn't a poor design you would see them in commercial installations”
.
In fairness to G2BCX, I sure his design works well for him, but there is a vast difference between the lab and the field… which brings me to point number Two--
.
SpugEddy, I am going to step you aside - for after all you were the one asking the original questions. I’m telling you that these types of antennas may be in your future, but steer clear of them for now. Aside from the obvious quarter-wave ground plane, here are a few of my suggestions if you still want to build-
.
Try your hand at that coaxial collinear vertical- but do it by the book- no substitutions of coax’s, etc….. or try some of the other phased section collinears… the books are full of them. The nice about these- you can assemble them in fiberglass or PVC pipes to make them weather proof...and they can be grounded
One of my favorites- the fold’d dipole- they are mechanically as tough as bricks. You can stack them in phase for additional gain, if you wish, they are easy to build and tune….. And going back to the commercial standard analogy- look at any 2-way tower- they are the antennas of choice.
.
Personally, I like the design of the Ringo Ranger.. ..not only for their simplicity of design, but ease of tuning- not to mention their inherent static suppression- everything is at DC ground. In the field we use similar designs all the time on 400-420MHz. If you feel so inclined, they are easy to duplicate.
.
What I am trying to get across is to avoid the anecdotal stories of how great an antenna is to one particular person as compared to something else. Antennas are one highly charged subject for hams… so approach them like a scientist,--- for remember, you can get a brine soaked piece of string to radiate RF- and some might laud it to the heavens as the best thing since sliced bread.
.
…………….CF
.
.
If I get a few moments in the next couple of weeks I might put together a UHF “Slim Jim” design and run it thru a few lab tests of my own- stay tuned…….
majoco
Stirrer
Perhaps the reason for the J-Pole or the Slim Jim not being produced commercially is that they are mechanically complex which doesn't lend itself to mass production and also so site specific when tuning up. Mind you, there are many amateur antennas that need a fair bit of tweaking to get them to work adequately - some never do!
As CF says, the good old folded dipole has lasted years as mass produced TV antennas in atrocious weather conditions and survived well. I have a cut-down one as my VHF aero antenna still with the 300/75ohm unun and it works well, even in the 'shade' of a largish discone above it.
Spugeddy - it's been an interesting discussion - let us know what you finally decide. Hope we haven't overwhelmed you!
CF - G2BCX used a home-brew UHF 650MHz test bench - used a record player platter to rotate the scaled-down antenna, a single tube lecher line oscillator and recorded the results on a pen'n'paper plotter. I suspect you may have something a little more sophisticated!
As CF says, the good old folded dipole has lasted years as mass produced TV antennas in atrocious weather conditions and survived well. I have a cut-down one as my VHF aero antenna still with the 300/75ohm unun and it works well, even in the 'shade' of a largish discone above it.
Spugeddy - it's been an interesting discussion - let us know what you finally decide. Hope we haven't overwhelmed you!
CF - G2BCX used a home-brew UHF 650MHz test bench - used a record player platter to rotate the scaled-down antenna, a single tube lecher line oscillator and recorded the results on a pen'n'paper plotter. I suspect you may have something a little more sophisticated!
Last edited:
According to the link. I am, in fact, mounted correctly. The 1 variation being
that I am mounted to a fence post mast and NOT pvc, but my mounting
point remains at the wavelength suggested. I'm approx. 20' from the earth
to the bottom of the antenna. This is taking me closer to the conclusion that
perhaps I AM too close to the A-99 antenna and its creating a problem.
I completely agree and I found a website years ago where a club measured the gain of several home made J-poles and 1/4 wave ground planes and found many of the ground planes outperformed the J-poles. This was because there are a lot of potential mistakes to be made putting together a J-pole type antenna compared to the almost impossible to mess up ground plane.
prcguy
prcguy
I have been following the discussion on these antennas -and several things strike me. First off, both the ‘J’ design and the “Slim Jim” are not Beginner’s Antennas-- especially! the later. I just read G2BCX’s article; I understand the theory behind this antenna; at the same time I can also see that building one by a neophyte is fraught with pit falls. Mechanically it is an awkward design. Constructing it to be stable enuff for long term out-of-doors would be challenging, there is no provision to ground it, the feed points are vague, and the use of twinlead feedlines makes me cringe (tho coax can be used) - these are among the detractors I found.
.
ND5Y sum’d it up: ….
“All I'm saying is if it wasn't a poor design you would see them in commercial installations”
.
In fairness to G2BCX, I sure his design works well for him, but there is a vast difference between the lab and the field… which brings me to point number Two--
.
SpugEddy, I am going to step you aside - for after all you were the one asking the original questions. I’m telling you that these types of antennas may be in your future, but steer clear of them for now. Aside from the obvious quarter-wave ground plane, here are a few of my suggestions if you still want to build-
.
Try your hand at that coaxial collinear vertical- but do it by the book- no substitutions of coax’s, etc….. or try some of the other phased section collinears… the books are full of them. The nice about these- you can assemble them in fiberglass or PVC pipes to make them weather proof...and they can be grounded
One of my favorites- the fold’d dipole- they are mechanically as tough as bricks. You can stack them in phase for additional gain, if you wish, they are easy to build and tune….. And going back to the commercial standard analogy- look at any 2-way tower- they are the antennas of choice.
.
Personally, I like the design of the Ringo Ranger.. ..not only for their simplicity of design, but ease of tuning- not to mention their inherent static suppression- everything is at DC ground. In the field we use similar designs all the time on 400-420MHz. If you feel so inclined, they are easy to duplicate.
.
What I am trying to get across is to avoid the anecdotal stories of how great an antenna is to one particular person as compared to something else. Antennas are one highly charged subject for hams… so approach them like a scientist,--- for remember, you can get a brine soaked piece of string to radiate RF- and some might laud it to the heavens as the best thing since sliced bread.
.
…………….CF
.
.
If I get a few moments in the next couple of weeks I might put together a UHF “Slim Jim” design and run it thru a few lab tests of my own- stay tuned…….
I'm no more overwhelmed than I was when I started. In fact, I'm less overwhelmed
because I've learned a few things. This is the main reason I post here. Sure, I can
read and read and read some more and I will get something from it, but by coming
here and posting the question, sometimes I get the "dumbed down" or the "layman's
terms" answer I'm looking for. And yes, sometimes it seems like I am constantly
"stepping in $#it" with some of my projects, but my philosophy has always been "if
I'm gonna step in it, why just cover the bottom of my shoe? Go for the biggest pile
and get the whole foot in it" That has been my whole life and I have learned an awful
lot along the way.
If you noticed, I never argue back with those offering advice (like some others here)
I absorb everything. Even if it is NOT the answer I was seeking.
Sometimes taking a little piece of 3 or 4 posts and using those as ingredients will
make my "recipe" better.
Some of you guys have given me great information in the past. Mmckenna, prcguy,
Coyote-Frostbite, majoco, and others. You have the knowledge that I don't have
and while I'm reading your posts, I see you as teacher and myself as student.
Now back to the meat and potatos. I think I am taking Coyote's suggestion. This
may be a project for further down the road when I become more educated. For
now I'll just stick to the very basics. I've already made several antennas but the
design has been simple (dipoles, 1/4 waves. etc.) Collinear looks basic but some
of the builds looked a little sloppy to me. Even my first attempt was disastrous. I'm
a neat freak when it comes to soldering and construction. I learned electronics
under the US Navy's Weapon Spec. WS-6536 years ago when I worked on the
Aegis Radar system. I have an idea in my head and now I want to try. I'll update
some progress here.
Thank you all for your input
Not even a little bit. Thank you
Before I leave this topic completely- another something for me to smile about- courtesy of Majoco
.
Lecher Lines !
.
I haven’t heard anyone use that term in years, let alone ever seen them in serious use.
What am I talking about?…Ahhh…an interesting research subject into historic radio--
.
I will relate, however, my limited experiences with them-, for those in the know; and how they bought me a few beers as a grad student teaching assistant.
.
For those not familiar with Lecher Lines, they were used as one of the earliest measures of V/UHF wavelengths**- which can then be translated into frequency. There are two parallel lines loosely coupled to the RF source under measurement. By sliding a detector down between the wires, its possible to detect the voltage nodes- you measure the distance in metric and determining wavelength. The technique dates to the early 1900’s and in hands of someone skilled at Lecher Wires, could result in frequency determinations of <1% error.
.
I would set up a lab demonstration for undergrad classes using two parallel bare copper wires spaced about four inches apart, running ~30 feet down the centre of the room- 6 feet high. To these wires, thru a loose link coupling, I’d match a signal source between 60-85 Mhz of several watts.
After a brief lecture about Lecher Lines and their historical place in RF engineering--- I would bet the class a round of beer at the campus ratskeller that they couldn’t measure the wavelength at better than +/- 500Khz. They always took the bet.
.
And I never bought a beer.
.
So much for history- the fine art of Lecher Line wavelength measurement; relinquish'd to the history books
.
.
…………………CF
.
.
__________________________________________
** I know Lecher Lines can form the tank circuits for amplifiers and free running oscillators, but limit this to wavemeters
.
Lecher Lines !
.
I haven’t heard anyone use that term in years, let alone ever seen them in serious use.
What am I talking about?…Ahhh…an interesting research subject into historic radio--
.
I will relate, however, my limited experiences with them-, for those in the know; and how they bought me a few beers as a grad student teaching assistant.
.
For those not familiar with Lecher Lines, they were used as one of the earliest measures of V/UHF wavelengths**- which can then be translated into frequency. There are two parallel lines loosely coupled to the RF source under measurement. By sliding a detector down between the wires, its possible to detect the voltage nodes- you measure the distance in metric and determining wavelength. The technique dates to the early 1900’s and in hands of someone skilled at Lecher Wires, could result in frequency determinations of <1% error.
.
I would set up a lab demonstration for undergrad classes using two parallel bare copper wires spaced about four inches apart, running ~30 feet down the centre of the room- 6 feet high. To these wires, thru a loose link coupling, I’d match a signal source between 60-85 Mhz of several watts.
After a brief lecture about Lecher Lines and their historical place in RF engineering--- I would bet the class a round of beer at the campus ratskeller that they couldn’t measure the wavelength at better than +/- 500Khz. They always took the bet.
.
And I never bought a beer.
.
So much for history- the fine art of Lecher Line wavelength measurement; relinquish'd to the history books
.
.
…………………CF
.
.
__________________________________________
** I know Lecher Lines can form the tank circuits for amplifiers and free running oscillators, but limit this to wavemeters
majoco
Stirrer
....and that's almost word for word the 'experiment' we had to do in the early 60's when I was studying to be a marine radio officer, except for the beer bribery! The detector was a low powered flashlight bulb and we had to interpolate where the null was between two glimmers of the filament. I'm sure if I went up into the roof space I could find my old notes somewhere..... perhaps not!
I wonder if there's scope for a paper entitled "does the anticipation of beer enhance the accuracy of the experiment results".
I wonder if there's scope for a paper entitled "does the anticipation of beer enhance the accuracy of the experiment results".
Last edited:
majoco
Stirrer
Now I've thought about it a bit more, ISTR that the lecher lines were lengths of "O" gauge model railway line and the detector was the chassis of a rail wagon on plastic wheels of course!
I'm a little late to the party, but what the heck. I had the same thought about J-Poles not being used commercially, but after a little digging I found that they are. Commercial J-Poles just don't look like your average copper pipe antenna. Commercial J-Poles are usually housed in a fiberglass tube. Here's something I wrote for another forum.
"So what's in the white tube that's on my roof now, and in all the white tubes that I've been looking at over the last couple of months? I got curious today and decided to find out. Antenna manufacturers aren't very forthcoming with design specifics, but with a bit of digging I unearthed some answers. The three brands that I see being sold the most on the Internet are Laird, Tram-Browning, and PCTEL. Laird and Tram-Browning antennas look identical. They have white fiberglass tubes with a gold top cap and a gold base. They are probably the same antennas sold under a different name. Laird makes around 65 models covering from 140 Mhz to 2.4 Ghz. They all look the same, with the exception of length, and they are all J-Pole or Collinear J-Pole designs. Tram-Browning doesn't specify their construction, but since they look exactly the same, right down to the stickers, as the Lairds then I assume they are J-Poles too. PCTEL doesn't say specifically how their antennas are constructed, but they do refer to their antennas as "base matched half wave antennas", which sounds like a J-Pole to me. They are also referred to as DC grounded, which is another characteristic of J-Poles. I looked at other brands that I'm not familiar with and found a mixture of J-Poles and collinear dipoles. I saw a loose association indicating that collinear dipoles were used in more expensive antennas, but it wasn't conclusive. All these antennas are commercial, not Ham, and even though some are designated as repeater antennas, I feel they would be more at home on the roof of a business. Not on a mountain at a repeater site. Seeing how many commercial antennas are using the J-Pole design, it gives me confidence that J-Poles are tried and true. They aren't just antennas that amateurs make with twin lead or copper pipe."
Here's another part of the post. I'm just learning about J-Poles so take my opinions for what they are worth.
"I would like to summarize what I think I know about the two types of antennas. Overall there's no big difference between the performance of the two antenna types, but each excels in its own way. A groundplane is simple, functional, is less prone to produce common mode current on the feed line compared to a J-Pole, and can be easy to build and tune for those that are so inclined. A J-Pole is a more complex design, has the potential for a bit more gain (up to 1.5 dB), is more likely to require a choke to suppress common mode current, can be safer in electrical storms without the addition of a suppressor, and is not as easy to build and tune as a groundplane. User's subjective reports on J-Poles seems to be more varied than with groundplanes. Perhaps this is due to the J-Pole design's sensitivity to build quality and materials. It's one thing to build a functional J-Pole, but it's another thing to get everything just right to get the most out of the design. Maybe some of the complaints about J-Pole performance has to do with poorly constructed or tuned antennas."
The J-Pole revisited.
I have a few questions for anybody who is able to help
Below is a pic of the "official" Arrow J-Pole antenna.
Lets say, from left to right the elements are "A" "B" and "C"
Then a pic of my homebrew J-Pole
Being a single band antenna, my build eliminates the long
element C. (I'm only using it for UHF) I changed the lengths
accordingly.
A (long element) = 18½"
B (short element) = 6"
What is each element called? What does it do?
Do I need element C?
Do my lengths look correct?
I have a few questions for anybody who is able to help
Below is a pic of the "official" Arrow J-Pole antenna.
Lets say, from left to right the elements are "A" "B" and "C"
Then a pic of my homebrew J-Pole
Being a single band antenna, my build eliminates the long
element C. (I'm only using it for UHF) I changed the lengths
accordingly.
A (long element) = 18½"
B (short element) = 6"
What is each element called? What does it do?
Do I need element C?
Do my lengths look correct?
Attachments
Arrow J-Pole revisited
I should add: I do not have an antenna analyser. I do have
a JTWVU swr / power meter.
My original design for this antenna had the tops of each
element threaded and fitted with a 3/8" coupler. Just turning
the coupler up or down would be the SWR adjustment. I didn't
seem to make a tremendous difference so I did away with the
threads at the top. If you think they should be put back, please
let me know.
Any comments about this build are welcome.
I should add: I do not have an antenna analyser. I do have
a JTWVU swr / power meter.
My original design for this antenna had the tops of each
element threaded and fitted with a 3/8" coupler. Just turning
the coupler up or down would be the SWR adjustment. I didn't
seem to make a tremendous difference so I did away with the
threads at the top. If you think they should be put back, please
let me know.
Any comments about this build are welcome.
Last edited:
Not sure you are going the right direction with this. On the original Arrow antenna, the long element (C) is 3/4 wavelengths long on 2m and for an actual J-pole the bottom 1/4 wavelength of element C would run parallel with a 1/4 wavelength grounded stub that is tapped at a 50 ohm point and only the top 1/2 wavelength of the long element would be the radiating part of the antenna.
The Arrow antenna is not really a J-pole and they appear to be exciting the long element C as a sympathetic radiator from a nearby 1/4 wave monopole (A) tuned to 2m. The 1/4 wave monopole A will also resonate as a 3/4 wave monopole in the 440 band and the little 6" long grounded stub thing (B) is either for impedance matching or its a sympathetic radiator for the 440 band. Would have to fire up EZNEC to really find out but I'm not motivated right now.
If your making just a UHF version of the Arrow I would think you would have a 6" spike on the connector as a resonant 1/4 wave at 440MHz (A) and have a grounded 3/4 wave sympathetic radiator right next to it (C). The goal would be to excite the 3/4 wave grounded element and have only the top 1/2 wavelength radiate if the spacing between the elements creates the equivalent of a 1/4 wave long transmission line which would not radiate under ideal conditions. You would probably not have a B element unless you were making a dual band 440/1,320MHz antenna and then element B would be about 2" long.
Since I think the design of the Arrow antenna is hogwash, I would not put a lot of work into trying to copy just part of it and expecting a good outcome.
The Arrow antenna is not really a J-pole and they appear to be exciting the long element C as a sympathetic radiator from a nearby 1/4 wave monopole (A) tuned to 2m. The 1/4 wave monopole A will also resonate as a 3/4 wave monopole in the 440 band and the little 6" long grounded stub thing (B) is either for impedance matching or its a sympathetic radiator for the 440 band. Would have to fire up EZNEC to really find out but I'm not motivated right now.
If your making just a UHF version of the Arrow I would think you would have a 6" spike on the connector as a resonant 1/4 wave at 440MHz (A) and have a grounded 3/4 wave sympathetic radiator right next to it (C). The goal would be to excite the 3/4 wave grounded element and have only the top 1/2 wavelength radiate if the spacing between the elements creates the equivalent of a 1/4 wave long transmission line which would not radiate under ideal conditions. You would probably not have a B element unless you were making a dual band 440/1,320MHz antenna and then element B would be about 2" long.
Since I think the design of the Arrow antenna is hogwash, I would not put a lot of work into trying to copy just part of it and expecting a good outcome.
Arrow J-Pole revisited
I found this today and it really just adds to my confusion.
I'm not quite sure I understand what the {Lambda/2}
on Element C means.
As mine is setup,
"A" is 3/4 wave (18")
"B" is 1/4 wave (6")
Then according to the drawing below,
"C" would be 3/4 wave + 1/2 wave?
Therefore, 3/4+1/2 = 5/4 or 18" + 12" = 30"
Wavelength of 465 Mhz is 25.38 Inches
1/4 wave would be 6.34"
1/2 wave = 12.68"
3/4 wave = 19.03"
5/4 wave = 31.72"
Apparently, according to the narrative,
the top section of element "C" {Lambda/2}
is the radiating section of the antenna and the
bottom {Lambda/4} sections are the matching
unit. And the small "B" element would be set
at the 50Ω mark.
The question is; are my interpretations correct?
I found this today and it really just adds to my confusion.
I'm not quite sure I understand what the {Lambda/2}
on Element C means.
As mine is setup,
"A" is 3/4 wave (18")
"B" is 1/4 wave (6")
Then according to the drawing below,
"C" would be 3/4 wave + 1/2 wave?
Therefore, 3/4+1/2 = 5/4 or 18" + 12" = 30"
Wavelength of 465 Mhz is 25.38 Inches
1/4 wave would be 6.34"
1/2 wave = 12.68"
3/4 wave = 19.03"
5/4 wave = 31.72"
Apparently, according to the narrative,
the top section of element "C" {Lambda/2}
is the radiating section of the antenna and the
bottom {Lambda/4} sections are the matching
unit. And the small "B" element would be set
at the 50Ω mark.
The question is; are my interpretations correct?
Attachments
- Status
