J-Pole build questions

[ntsqd]

After reading about the AdventureDuo's trick new radio set-up on their trailer I got to seriously thinking to build a J-Pole antenna for use in temporary base station set-ups in remote areas. My use is simplex, though I'm not sure how that might matter. Regions that it will be used in range from nearly flat to hilly, but not what Left Coasters would call mountainous.

My questions are mostly about construction of the antenna. Most of the online articles on building these, and there are a lot of them, use 1/2" copper tube. Because of availability and the rough country transport I started making mine from 3/4" tube. Any idea how this will affect antenna performance?

I am also thinking to make it collapsible by adding a second 'T' to the main tube at about the height of the 'J' tube's top. The idea being that I can then rigidly bridge the gap with some PVC tube and a PVC elbow while making the upper portion of the main tube removable for transport. It would, of course, be trimmed to offset the length gain from placing the 'T' in that section. My concern is that changing the shape (due to the 'T') in the middle of the main tube might affect performance of the antenna or tend to make it slightly directional.

I am also under the impression that the J-Pole should not be common with the vehicle's frame (i.e. the radio's power supply ground)?

I've also elected, again due to the rough transport issue, to use silver solder instead of soft solder to make all of the joins. Any comments on this?

 

[SunTzuNephew]

Using 3/4 wont affect the performance at all. And no, it shouldn't be grounded...

 

[thallca]

You might want to look into J-pole antennas made by Arrow Antennas at www.arrowantennas.com
I got one after reading a review in the March 2010 QST mag. They are super easy to put together and very strong. The best part was the fact that is was only $39.

 

[1leg]

I bought an OSJ 146/440 arrow J-pole at HRO on sale for about 25 bucks i think. I mount it to a extending paint pole that extend to 10 ft. When i had the jeep I would mount it to milk crate and strap the crate to the spare tire rack. This got the bottom of the pole to about 15 feet into the air to tip is around 18 to 20.
This set-up works great for mobile base station set-up.

 

[AKRover]

I made a copper pipe j pole that was straight out of the arrl antenna book and it works great. The main section is made from 3/4 and the matching stub is made from 1/2. If you don't have the book I could scan you that page and email it if you wanted.

To make it collapsable you could just skip soldering the bottom joint and add a slip joint in the middle of the main element.

I have see those fiberglass poles that were used in the other thread online before and was never really sure of the quality. After seeing it put to use though I'm considering one myself and making a collapsable j pole to put on it is a great idea. It would also give my buddiepole quite a bit more Hightower above ground.

 

[gary in ohio]

If you want a truly portable antenna, look at the "rollup" jpoles, Made from twin lead or 450ohm balanced feedline.

 

[AKRover]

If you want a truly portable antenna, look at the "rollup" jpoles, Made from twin lead or 450ohm balanced feedline.

That would work pretty good. Then you could just hang it down from the top of the mast.

 

[SunTzuNephew]

That would work pretty good. Then you could just hang it down from the top of the mast.

Or tie a piece of string to it and toss it up in a tree. And when you're done, roll it up and stick it in your pocket.

 

[ntsqd]

Thanks for all of the input!

This is where I'm at thus far. Note that the long upper tube has not yet been soldered into place:

What I'm proposing to do with the PVC section would look like this, only soldered in place. What isn't visible is that there is a short section of PVC pipe that would be glued into the elbow and threaded into an insert in the upper 'T':

I can see how the normal slip fits of the fittings aren't very robust. That has been one of my lessor concerns. I'll look into the repair pipe option.

I wasn't worried about rain water running through the antenna tubes themselves. I figured wet on the inside isn't any different than wet on the outside. I'm only using the PVC elbow to cap off the short leg because it is an easy way to capture the top of the short leg. The shock-cording idea is interesting though, I'll give some thought to that one.

I have a piece of G10 on order. My plan is to use it to isolate the antenna from the mast and to mount the SO259 or a bulkhead connector - which ever looks to work the best when I get to that point.

For me the roll-up is out. Not enough trees in the intended use area to be a reliable method, and wind would require that it be secured to the mast for it's whole length - which shortens the effective mast height by the length of the antenna.

 

[xtatik]

FYI,
There is a company out here (SoCal) that makes a breakdown copper pipe J-Pole. The name of the company is JamesPole. They put a simple threaded male/female NPT joint midway up the radiating side so it essentialy unscrews and breaks down to half size. They are stocked at and can be purchased from HRO. They are pre-tuned and run about 30 to 40 bucks as best I can remember. They can be had from ther website as well, but I think they cost more direct.
http://www.jamespole.net

 

[cruiseroutfit]

I've got a 'break-down' copper j-pole that was built by a local club member. All of the joints screw together and you simply pound the bottom piece into the ground and assemble it from there. Worked really well during a desert trip. I'll grab some pics of the setup. I can't say it works better/worse than the setup your designing with the PVC elbow but I will say that this one not only worked good enough but it stored so compact that I'm planning to make one myself. I've got a standard j-pole that I may dissect, though the parts to make them are cheap enough I may just start from scratch?

 

[ntsqd]

I don't know what the copper tube/pipe would cost as it was extra laying around (partly what drove the 3/4" size selection). I'm up to about $15 in fittings etc. so far.

One downside for me in using screw together fittings is that silver soldering happens at a high enough temperature that it removes the work hardening of the wrought fittings. So the threads would be dead soft and subject to galling rather easily. Otherwise it would be my preferred method for a collapsing antenna.

EDIT: Meant to include this link: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=9284

 

[taugust]

I recently found this article for building a folding J-pole antenna. Very similar to the current discussion. There is a pdf of the article on the page.

http://ka0zlg.web-features.com/

 

[BigJim]

I have a J-Pole

I made out of 300 Ohm TV twin lead. I soldered a nice 15 foot piece of RG58 to it and use it for backpacking and remote camping.

It folds up very nicely and works IMO as well as a hard metal antenna.

My .02

After reading about the AdventureDuo's trick new radio set-up on their trailer I got to seriously thinking to build a J-Pole antenna for use in temporary base station set-ups in remote areas. My use is simplex, though I'm not sure how that might matter. Regions that it will be used in range from nearly flat to hilly, but not what Left Coasters would call mountainous.

My questions are mostly about construction of the antenna. Most of the online articles on building these, and there are a lot of them, use 1/2" copper tube. Because of availability and the rough country transport I started making mine from 3/4" tube. Any idea how this will affect antenna performance?

I am also thinking to make it collapsible by adding a second 'T' to the main tube at about the height of the 'J' tube's top. The idea being that I can then rigidly bridge the gap with some PVC tube and a PVC elbow while making the upper portion of the main tube removable for transport. It would, of course, be trimmed to offset the length gain from placing the 'T' in that section. My concern is that changing the shape (due to the 'T') in the middle of the main tube might affect performance of the antenna or tend to make it slightly directional.

I am also under the impression that the J-Pole should not be common with the vehicle's frame (i.e. the radio's power supply ground)?

I've also elected, again due to the rough transport issue, to use silver solder instead of soft solder to make all of the joins. Any comments on this?

 

[ntsqd]

I suspect that if soft-soldered that using the threaded adapters wouldn't be too big of an issue. They don't have to go leak-tight, so that will save a lot of galling potential. I would use something like dry graphite on the threads for lubrication just to be sure. Be careful to not use an insulating lubricant (like teflon tape) and I wouldn't have a problem with using threads to make the antenna collapsible. It's just that my use of silver solder makes the copper dead soft, and then the threads won't work so well.

Made some progress last night, but ran up against not having any flux. I took the upper 'T' to the belt sander and removed most of the branch socket. This puts the female threads further away from the short tube. Hope to finish or nearly finish brazing it tonight.