I built the same "J"-Pole as Bharvey2 - for my situation it works great. It is difficult to get the UHF portion to tune, however it can be made adjustable with a little extra work. This model of "J"-Pole I think looks better that the Copper Cactus, which can also be made in a dual band version. When it is mounted on top of you house, you have to make sure the XYL won't object. I think if I put up the Copper Cactus she would think it was some plumbing mistake I made during the kitchen remodel. : )
2 meter j-pole
- Thread starter andrewvickery1
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Threads concerning j-poles are so common here they should have their own section.
A j-pole is an end-fed half wave or Zepp antenna. It presents a balanced load. It should be fed with a balun or directly fed from the bottom. Look at Arrow antennas j-poles for an example of direct fed antennas.
They don't need to be isolated from the mast.
Poor results and difficulty tuning are the result of the feed being done incorrectly.
Having said all that, and I've said it before on other threads, there will be a chorus of:
1. It's not a balanced loan.
2. It doesn't need a balun.
3. You can't feed it from the bottom.
4. Ground planes are just as good.
5. J-poles don't work.
Have fun.
A j-pole is an end-fed half wave or Zepp antenna. It presents a balanced load. It should be fed with a balun or directly fed from the bottom. Look at Arrow antennas j-poles for an example of direct fed antennas.
They don't need to be isolated from the mast.
Poor results and difficulty tuning are the result of the feed being done incorrectly.
Having said all that, and I've said it before on other threads, there will be a chorus of:
1. It's not a balanced loan.
2. It doesn't need a balun.
3. You can't feed it from the bottom.
4. Ground planes are just as good.
5. J-poles don't work.
Have fun.
paulears
Member
When I was first licenced in the late 70s, all the local hams were employed by the Government, the TV manufacturing industry, science, BT, the armed forces and were a pretty capable lot compared to me. Fred Judd, G2BCX was a curmudgeonly old fella who lived about ten miles away, and having invented the Slim-Jim, based of course on the J-Pole design promoted it over the usual dipoles most people used for 2m. in almost 40 years exactly the same arguments are going on. Ribbon feeder and baluns inside the shack were so common, and few people had antenna farms, usually just a simple 2m vertical on the TV antenna pole on the chimney, and a long wire, or zepp, or often a variety of horizontal dipoles and ATUs for HF. 2m was for chat before my generation, and us newcomers were into 2m DX with horizontal beams a rotators.
Fred was really a grumpy old git to be honest, and 145.550 at 8am was HIS frequency, and anyone else appearing on that channel at that time got chased of pronto by the old boys net. Fred would always be banging on about how good the Slim Jim was compared to the J-Pole, and cite all his research and evidence, and the other old fellas used slim jims simply to keep him quiet. Back then, I had trouble working out how it worked, and what exactly the benefits were over my 1/4 wave and coathanger ground plane. I still remain just as unconvinced today.
Nice to see the same discussions are now worldwide, and just as polarised!
Fred was really a grumpy old git to be honest, and 145.550 at 8am was HIS frequency, and anyone else appearing on that channel at that time got chased of pronto by the old boys net. Fred would always be banging on about how good the Slim Jim was compared to the J-Pole, and cite all his research and evidence, and the other old fellas used slim jims simply to keep him quiet. Back then, I had trouble working out how it worked, and what exactly the benefits were over my 1/4 wave and coathanger ground plane. I still remain just as unconvinced today.
Nice to see the same discussions are now worldwide, and just as polarised!
"Poor results and difficulty tuning are the result of the feed being done incorrectly."
I guess I will hold off a little on responding to this as I have not checked my Bury Flex Coax from the antenna to the radio for problems.
I know that on 2m I have an SWR of 1.2:1 and on 70cm I have SWR of 2.5:1. The 70m stub is shorter (6 9/16 as opposed to 6 3/4) than the one used in the Arrow Manufactured units. The longer (6 3/4) gave me a much higher SWR on 70cm than the 2.5:1 I get now. I tried a 6 3/8 and it was more than 3.0:1 also.
I do have the 4 to 6 loops of coax that is suggested, though it is about 6 feet below the antenna and not 12 inches below the antenna.
One of the things about DIY antenna building is the experimentation. I plan to take an SWR meter to the roof with a short jumper and check SWR at the base of the antenna. If I could get the 70cm to less than 2.0:1 I would be happy.
I guess I will hold off a little on responding to this as I have not checked my Bury Flex Coax from the antenna to the radio for problems.
I know that on 2m I have an SWR of 1.2:1 and on 70cm I have SWR of 2.5:1. The 70m stub is shorter (6 9/16 as opposed to 6 3/4) than the one used in the Arrow Manufactured units. The longer (6 3/4) gave me a much higher SWR on 70cm than the 2.5:1 I get now. I tried a 6 3/8 and it was more than 3.0:1 also.
I do have the 4 to 6 loops of coax that is suggested, though it is about 6 feet below the antenna and not 12 inches below the antenna.
One of the things about DIY antenna building is the experimentation. I plan to take an SWR meter to the roof with a short jumper and check SWR at the base of the antenna. If I could get the 70cm to less than 2.0:1 I would be happy.
I agree with you Paul- I don't understand the almost fanatical interest in the "J" antenna. It gets hash'd and rehash'd over and over-and like it was said- it is (almost) deserving of its own forum topic.
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I want to throw out a caveat before launching into any criticism of the "J"- I think as far as any antenna goes, this is one of them.**
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Nothing stellar, nothing to notify the Nobel Committee on Physics about. So for those with a passionate attachment to its design, I say; "Good one ta' ya, Mate, knock yourself out"
.
That said, I think the traditional "J" is an awkward design- if done classic.... and in classic I mean like its origins- the "Zepp".... not some variation that takes its name "J" from its physical appearance. Physically they tend to myriad weakness's; and as pointed out earlier there are no commercial versions of them in use.... for those good reasons.
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I have looked at how they model, and they are not much different than a 5/8 wave vertical. 5/8's presents a matching issue, but anyone with patience can resonate a tap'd coil at its base. But the 5/8's is a vastly superior antenna strength wise- as evidenced by the millions in commercial use.
Continuing on; A 3/4 wave vertical is simplicity in itself, and exhibits radiation patterns close to a "J".... I won't even mention using a simple quarterwave for ease of construction and operation... why mess with the awkward "J" ? (want an interesting low angle of radiation with a 1/4 wave?- invert it... we do that all the time at high elevations.).... or maybe?... a half wave vertical dipole..............
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Me thinks perhaps there is something magical attached to the "J",... a certain mystique.. born of urban legends- handed down from ham to ham like a holy relic. I think if someone made an issue and highly promoted wet string as the ultimate VHF antenna, there would arise an unscientific following of the unwash'd.
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Pesonally if someone was interested in building antenna, I'd steer them in some other directions too.
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............................CF
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_______________________________________________________
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*I extracted this from a trite old saying: "....of all the Townes in all the States... we are one of them... !"
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damning with faint praise.....
.
I want to throw out a caveat before launching into any criticism of the "J"- I think as far as any antenna goes, this is one of them.**
.
Nothing stellar, nothing to notify the Nobel Committee on Physics about. So for those with a passionate attachment to its design, I say; "Good one ta' ya, Mate, knock yourself out"
.
That said, I think the traditional "J" is an awkward design- if done classic.... and in classic I mean like its origins- the "Zepp".... not some variation that takes its name "J" from its physical appearance. Physically they tend to myriad weakness's; and as pointed out earlier there are no commercial versions of them in use.... for those good reasons.
.
I have looked at how they model, and they are not much different than a 5/8 wave vertical. 5/8's presents a matching issue, but anyone with patience can resonate a tap'd coil at its base. But the 5/8's is a vastly superior antenna strength wise- as evidenced by the millions in commercial use.
Continuing on; A 3/4 wave vertical is simplicity in itself, and exhibits radiation patterns close to a "J".... I won't even mention using a simple quarterwave for ease of construction and operation... why mess with the awkward "J" ? (want an interesting low angle of radiation with a 1/4 wave?- invert it... we do that all the time at high elevations.).... or maybe?... a half wave vertical dipole..............
.
Me thinks perhaps there is something magical attached to the "J",... a certain mystique.. born of urban legends- handed down from ham to ham like a holy relic. I think if someone made an issue and highly promoted wet string as the ultimate VHF antenna, there would arise an unscientific following of the unwash'd.
.
Pesonally if someone was interested in building antenna, I'd steer them in some other directions too.
.
.
............................CF
.
.
_______________________________________________________
.
*I extracted this from a trite old saying: "....of all the Townes in all the States... we are one of them... !"
.
damning with faint praise.....
Last edited:
majoco
Stirrer
CF said:
So here's my Slim Jim that I made in the early 80's - works and still works for me. Aluminium rods 6mm diameter on the outside of a length of 32mm waster pipe fed directly from coax onto the bottom stub, experimented with an antenna analyser before setting on the final matching point. There is NO connection to the mounting mast and NO balun/braid breaker in the feed line.
So here's my Slim Jim that I made in the early 80's - works and still works for me. Aluminium rods 6mm diameter on the outside of a length of 32mm waster pipe fed directly from coax onto the bottom stub, experimented with an antenna analyser before setting on the final matching point. There is NO connection to the mounting mast and NO balun/braid breaker in the feed line.
Attachments
A nice construction job ! Majoco - But then you cheated !... that antenna adheres to all the best principles of a tru "J Pole"--- not the strange SteamPunk "J" contraptions made out of twinlead, loopy coax baluns and rusty coat hangers so often tout'd.... Smiles!
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.........................CF
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.........................CF
That looks nice!
I am not sure I understand your emphasis on the lack of a method to help control common mode current.
All of the basic j-pole antennas are balanced antennas. It they are fed with unbalance coaxial cable there will be common mode current on the feed line.
All though each installation will be different, this can cause issues with the RF pattern of the antenna and noise immunity of the feed line. The impact of these will vary with each installation.
Common mode current on the feed line is very easy to verify and detect. The impact on the RF pattern of the antenna is easy to verify and measure.
There are those that say a j-pole antenna works great (ignoring common mode current and RF pattern variability and degradation) and in their specific situation this is likely true, but it does not change the basic science of the antenna and feed line.
For those that would like to experiment with a j-pole antenna it is not a bad idea to consider dealing with the common mode current.
In one of my other hobbies I might be considered an audiophile or sometimes referred to as an audiofool...
In any event a lot of use still like to use old fashioned, analog FM stereo tuners and receivers. And at times the stations that we want to receive are outside of the 60 dBµ contour of the station (this means the signals are somewhat weak).
One of the popular DIY antennas is the j-pole. In the above situation dealing with common mode current and the noise immunity of the feed line helps assure that the antenna is working as good as it can and can make a somewhat noisy signal listenable.
Again, your installation looks good and if it works for you in your particular application, all is good.
Probably the best analysis has always been here, just a little bit down the page about J-poles:
https://www.w8ji.com/end-fed_vertical.htm
It all depends on what radiation angle works for you. Swap the center and coax braid around and see. Add radials - and so forth.
The common mode interaction makes it work great for some but not for others. Depends on what you are trying to achieve. Try a few different configurations, and see if it works for you.
Purists will note that it is:
1) An end-fed half-wave radiator. An unbalanced condition being fed at one end like that.
2) A quarter wave matching transformer. This part is balanced.
3) Coaxial feedline. An unbalanced condition.
Going from unbalanced > balanced > unbalanced can lead to issues!
Thing is, these issues may be totally acceptable to some, or a deal-breaker to others. Experiment to see if it matters in your application or not.
https://www.w8ji.com/end-fed_vertical.htm
It all depends on what radiation angle works for you. Swap the center and coax braid around and see. Add radials - and so forth.
The common mode interaction makes it work great for some but not for others. Depends on what you are trying to achieve. Try a few different configurations, and see if it works for you.
Purists will note that it is:
1) An end-fed half-wave radiator. An unbalanced condition being fed at one end like that.
2) A quarter wave matching transformer. This part is balanced.
3) Coaxial feedline. An unbalanced condition.
Going from unbalanced > balanced > unbalanced can lead to issues!
Thing is, these issues may be totally acceptable to some, or a deal-breaker to others. Experiment to see if it matters in your application or not.
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