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[Articles Home]  [Add Article]  

The SIMPLE 2m Copper 'J' Antenna

Dale "Kuby" Kubichek, N6JSX /8 (N6JSX) on September 18, 2001
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the SIMPLE 2m Copper pipe "J"

by Dale “Kuby” Kubichek, N6JSX /8 03/2001

(To download a printable ms-word format file of this article, click here )

Can you use a pipe cutter or a hack saw, can you solder – then here is how to build a SIMPLE ”J” antenna that will more than double your 2 meter (and even 440) performance!

The "J" antenna goes back many years, long before I became a ham. There are a bunch of reasons why you're going to want to build one of these beauties:

“J” has the lowest angle of radiation,

“J” requires NO ground plane;

“J” is very easy and inexpensive to make;

“J” has great performance for mobile, marine, or base operations;

This “J” design can be used as a dual-band’er - 2m/440.

Technical:

The basic "J" is reported to have >3dB of gain over a ¼ l ground plane antenna and 6dB over an isotropic (theoretical) antenna. The "J" can be made from almost any material: copper pipe, steel whips, and even 300 ohm TV twin-lead.

Technically, the "J" antenna is an end-fed ½ l antenna that uses a ¼ l matching stub. Old-timers call it an "end-fed Zepp", bent 90°. In actuality, the conductor is ¾ l long and the matching section uses the bottom ¼ l. The matching stub creates the tuned ½ l length antenna.

Due to the matching section acting as the matching transformer, the ½ l radiator sees the lower ¼ l matching section as an image of a false ground plane. In best terms, the "J" is a balanced ¼ l matching stub feeding an unbalanced ½ l load.

The feed-lines to a "J" can be almost anything (ladder line to coax). However, in experimentation, I found RG-58/U coax to be best when used at odd ¼ wave multiples.

A “J” is the best for mobile and marine application where you want the most distance across relatively flat ground/water. A 5/8 or ¼ l antennas have a higher angle of radiation and need to be centered on a good ground plane eliminating gutter or vehicle edge mounting to obtain optimal performance. A "J" requires NO additional ground plane.

A “J” has an exceptionally low, to nearly flat, angle of radiation of about 0-2 degrees. The 5/8 l has about a 3-6 degree radiation angle and the highest radiation angle comes from the ¼ l that has about 4-10 degrees. These two antennas are usually better for mountain top (a few thousand feet elevated) repeater site use but will fall far short of a “J” in overall flat-land transmitting distance.

The pictured “J” is at 60’ on top my tower in Manitowoc, WI. I can now hit repeaters across Lake Michigan, Milwaukee, or Upper Michigan that are well over 85 miles away.

Parts:

The antenna pictured here is made from one 10’ piece of thick wall ¾” rigid copper pipe, one ¾” copper pipe “T”, one ¾” copper pipe 90° elbow, and three ¾” copper pipe caps, one SO-239 connector, and a 3” piece of 1/8” solid brass brazing rod (from a local welding supply company). These parts, plumbers flux, plumbers solder, and propane torch can be obtained at most hardware stores. Using copper pipe makes it easy to solder and snap to assemble. These materials will withstand a lot of abuse and weather. Total cost of this antenna was about $9.00.

I use ¾” thick wall copper pipe due to my ½” copper pipe “J” was bent in a 59 MPH wind gust last year. The ¾” thick wall is much stronger! Theoretically, the ¾” pipe should be slightly more broad banded but I’ve not measured any difference from ½” pipe “J”.

NOTE - about dimensions:

I’ve seen numerous articles on “how-to” build a “J” antenna with various dimensions. Everyone seems to have the secret of the optimal “J” design dimensions. I’ve made many “J” antennas and nearly everyone I’ve ever made has NEVER operated like the previous built “J” – they all required some tweeking to obtain “my perfectionist requirements” near 1:1 VSWR as possible! However, in general if you follow the dimensions I’ve included here you will have an antenna that will be less than 2:1 VSWR and more like 1.5:1 VSWR across the 2 meter band.

Recently, I’ve been experimenting with the basic “J” dimensions; I have found that a 2m J length of 63” really enhances the 440 band operation (63”=2.5 l at 445). The trade-off on 2m is an enhancement of a much wider bandwidth and an overall lower 2m VSWR. My J design dimensioned here is really great for single feed dual band operations!!!

Building: Basic dimensions for a 146.000 MHz. ¾” rigid copper pipe “J”

2m ¾” Copper pipe “J” Performance Data



The difference of this design over my previous designs is the change to the feed point attachment method. I did not like soldering the coax wires directly to the copper pipe these wires were exposed to the elements. The coax got very brittle, the center dielectric crack, and the coax eventually got water logged.

I experimented using a brass brazing rod. I’ve seen designs with the coax center conductor attached to the ¼l element or the ¾l elements. I found the best performance was to attach the coax center/brass rod to the ¾l element solder the brass rod to the ¾l element. Place the SO-239 into position and measure the rod then cut the rod accordingly. Sand off the finish of the backside of the SO-239 and tin this area. Insert the brass rod into the center conductor of the SO-239. Solder the SO-239 to the ¼l matching element. Make sure the brass rod/center conductor is NOT touching the ¼l matching element. Finish by soldering the brass rod to the center conductor.

NOTE: BEWARE of your heat used when soldering the SO-239 to the “J” or the center conductor insulator in the SO-239 will melt away or go off center!!!

Alternate feed method for ½” copper pipe “J”

Recently, I came across another very good feed point method for the ½” copper pipe “J” that eliminates the connector strain of the 90° coax loop. This design comes from the ARES group of Auglaize County, Ohio. The Auglaize ARES has installed this type of antenna on most all the Auglaize County Fire Department locations. They state they have made over 60 of these “J” antennas and have even sold them at Dayton. With the construction jigs created by WD8LLN mass-producing of identical “J” ‘s is a snap.

In conclusion:

I have found that the length of the attached coax does have an affect on the J’s VSWR. Multiples of odd ¼l lengths seem to minimize these coax affects. I have pruned off 3” pieces of coax in the HAM shack to bring the VSWR back to the 1:1 tuning the antenna was setup at. On VHF/UHF the VSWR variances are very susceptible to the consistency of the coax velocity factor and quality.

I've used copper pipe “J” in an apartment placing the antennas in the corners of the living room or hanging the "J" from curtain rods behind the curtains. I’ve even made a corner hat & coat rack from a copper pipe “J”.

The "J" offers the foundation for a stealth antenna by placing the antenna in PVC with an angled mounting box - the antenna can look like a gas/sewer breather pipe on the roof of CCR restricted house. NOTE: PVC/ABS/plastic will affect the J’s VSWR.

The TV twin lead “J” is the “BEST” hidden transmitter hiding antenna I’ve ever used. It can be wrapped around branches of a tree or laid on top tall grass next to a riverbed emitting complex angles of various polarizations that caused extreme multi-path. I’ve enclosed a TV twin-lead “J” inside a black ABS/white PVC pipe and buried the antenna and “T” just under the surface of the ground near a wire fence. The wire fence ran through the Puente Hills; the fence parasiticly re-radiating the 2 Watt signal for considerable distances in either direction, add to this the limited access to the area and the hunters were totally confused for many hours. I’ve taken this same PVC antenna and “T” creation and put it underwater in a creek – now that was fun to watch the hunters not wanting to get wet but wanting to win. (Note: PVC will detune an open air tuned TV twin-lead J.)

I take a wire wheel and steel wool to make my copper “J” antennas giving them a near military shine. Then I put multiple coats of Varithane (non-UV type) spray or Marine Spar varnish over the entire antenna - this will keep the antenna bright and tarnish/rust free for years. I even do this to my aluminum beams.

Other very good "J" antenna designs published in 73 Magazine have been;

Copper Cactus (2m) J-Pole by KE7AX, February, 1992.

220 Super J-Pole Antenna by KA0NAN, May 1996.

440 Super J-Pole Antenna by KA0NAN, April 1996.

Simple J-Type 10m Vertical by W6IOJ, Sept. 1995.

Copper Dual-Band Super J-Pole Antenna by KA0NAN, April 1993.

(can not obtain good VSWR on 440 but the 2m gain is outstanding – about 6dbd worth!)

EXPERIMENT, create you own unique designs the “J” is a very forgiving, yet, robust and fundamentally versatile antenna that can let YOU put the technical design, development, and building accomplishments back into HAM radio.

Member Comments:
This article has expired. No more comments may be added.
 
The SIMPLE 2m Copper 'J' Antenna  
by KB9VBR on September 18, 2001 Mail this to a friend!
The J is a great antenna. While I haven't built this particular J-Pole, I've constructed several using similiar plans. Every few monthes a group of us get together, invite the new hams and have an antenna party. Not only do the new people learn a little antenna theory, but go home with a great first antenna. They also get some practical plumbing experience that may come in handy some day.

Michael
KB9VBR
 
The SIMPLE 2m Copper 'J' Antenna  
by KE5GK on September 18, 2001 Mail this to a friend!
We need more thoughtful postings like this one. Good Job!
 
The SIMPLE 2m Copper 'J' Antenna  
by K7LA on September 18, 2001 Mail this to a friend!
An outstanding article.

I have constructed many J-antennas along this line and have used stainless steel rod with lucite braces for a bicycle mobile application obtaining superb results. Usually 1.5-2.5 watts is all I need to full quiet the area repeaters. No ground plane is required with the built-in counterpoise and you get great audio reports. This type of antenna is great for emergency and battery operations.

I urge all Technician hams to construct one of these antennas and put a little fun into your hobby, inexpensively!
 
RE: James-Pole Antennas  
by AD7DB on September 18, 2001 Mail this to a friend!
Good article!

For those of you who'd still like to just buy one rather than build one, contact James Pike KB6WHT, of Apple Valley CA. He builds these and sells them, and they are excellent quality. His website is at "www.jamespole.net".

Dave AD7DB
 
The SIMPLE 2m Copper 'J' Antenna  
by KC9AAI on September 18, 2001 Mail this to a friend!
Dale,

I constructed one of these earlier this summer with great success. I soldered the coax directly to the antenna and covered the exposed areas with Plasti-dip. I wasn't real comfortable with the connection though.

Based on your posting, I'm going to change mine over to the ARES design.

Thanks for the article!

Carl KC9AAI
 
RE: The SIMPLE 2m Copper 'J' Antenna  
by N3JIY on September 18, 2001 Mail this to a friend!
It looks very sturdy. Thank you for explaining how to make it.
I have a propane torch. Watch out! Are you able to open the
hatch on the back of your station wagon?
 
RE: The SIMPLE 2m Copper 'J' Antenna  
by KE4SKY on September 20, 2001 Mail this to a friend!
A very nice, practical treatment of the J-Pole antenna.
With your permission, I would like to use this as a handout for Virginia RACES.

73 de KE4SKY
Virginia State RACES Training Officer
 
The SIMPLE 2m Copper 'J' Antenna  
by KB1CJ on September 22, 2001 Mail this to a friend!
Has anyone tried the ARES design with 3/4 inch copper pipe, rather than 1/2 inch? That looks like a great idea.
 
RE: The SIMPLE 2m Copper 'J' Antenna  
by N6JSX on September 22, 2001 Mail this to a friend!
Hi The problem with using 3/4" for the ARES feed method is the SO-259 attachment. It fits well on 1/2" copper pipe but is really sloppy on 3/4" copper pipe. The dimensions are critical for this feed method too.


FYI for all - if you would like a copy of my MS Word .doc file zipped up let me know. The graphics are far better. The posting of my article on eHAM made my drawings very fuzzy and added a gray background making it more difficult to visualize. Email me a request and I'll email the file - the file size is about 700K zipped.

I'm in the process of creating a 220 J article for eHAM - should have that done in a few weeks. Hope you all liked this one - I got more if you want them.

73, Kuby, N6JSX /8 N6JSX@yahoo.com
 
The SIMPLE 2m Copper 'J' Antenna  
by KN4OO on September 25, 2001 Mail this to a friend!
Finally a "J" pole that actually works.

I stepped out on to the patio and built this antenna and the results were amazing I can now get into repeaters that were almost impossible before....cool
 
The SIMPLE 2m Copper 'J' Antenna  
by W4SDL on September 26, 2001 Mail this to a friend!
I have built and researched the "J" antenna.Built with same materials by the hundreds.
The SCATA system here is using them all over the city.
I use a TV balun ( 75 to 300 ohm type) to complete the unbalance to balance termination.
This worked all way up to thru 70 cm and 900 mhz too.
For vehicles I use a CB whip with AL clothes line wire and aluminum block to hold the
1/4 wave stub.Placing the array above the roof level it has unobstructed pattern with glass
fiber (box) tape 4" down to support the open end keeping it relatively parallel in the wind.
This antenna was the HF wire antenna with a heavy weight on the far end used on the
Zeppelin Air Ships, thus keeping the high voltage end away from the flamable gas bag.
 
RE: The SIMPLE 2m Copper 'J' Antenna  
by W4SDL on September 26, 2001 Mail this to a friend!
"J Pole " is incorrect. "J " antenna is the fundamental correct designation.
The "J pole " was a flag plole with several "J" antennas on different bands, written in QST
several years ago.
 
RE: The SIMPLE 2m Copper 'J' Antenna  
by KB3FIO on October 3, 2001 Mail this to a friend!
Would any of the dimensions of this design change if you used 1/2 copper? If so, how?
 
The SIMPLE 2m Copper 'J' Antenna - modified yet ag  
by KC0GNH on August 30, 2002 Mail this to a friend!
I've modifed the design using the original dimensions, but added an 3" stub making it an "abbreviated 'H'". The 3" stub has a panel-mount SO-239 through a 3/4" copper cap. The center connector is soldered to a 12 gauge piece of insulated copper wire which feeds up through the matching stub. I drilled a small hole in the matching stub large enough for a rubber grommet through which I passed the wire which is eventually soldered into a small hole in the main element. The whole thing can be assembled and soldered with absolutely NO heat-related damage to the insulator in the SO-239 by using a simple process.
There's a logical order of assembly with this version in which the radiator is soldered to the first "T", then its cap is soldered on to give a 63" length as shown in the article. The stub joining the "T"s is soldered to the first "T", then the second "T" is soldered to the stub. Then the 12ga wire is soldered to the bare SO-239 and set aside to cool. Drill the cap for the "abbreviated H" to accommodate the SO-239. Insert the nut for the SO-239 into the cap and jam it in place with the 3" stub. Solder the drilled cap to the stub and the stub to the bottom side of the second "T", and set it all aside to cool. Liberally coat the solder joint on the back of the SO-239 with some clear silicone, and squirt a liberal amount of silicone into the inside of the drilled cap. Gently push the 12ga wire through this silicone until it emerges from the other end of the second "T". Seat the SO-239 into the captive nut inside the drilled cap and screw it in tightly. Bend the 12ga wire to keep it centered in the second "T". Squirt more silicone down into the second "T" to insulate the back of the SO-239 and keep the 12ga wire pretty much centered in the tube. Place the reflector (19" piece) into the upper end of the second "T" and mark off 3.75" as shown in the article. Drill the reflector at that point for a rubber grommet, but don't insert the grommet yet. Bend the tip of the 12ga wire to slide through the just-drilled hole in the reflector and seat the reflector into the second "T", and solder it this time, being careful to not let the insulation on the 12ga wire come in contact with the hot copper. When it has cooled, slide the grommet over the 12ga wire and seat it into the hole. Drill a small hole in the radiator opposite the point where the 12ga wire emerges from the reflector. Bend the 12ga wire to be perpendicular to the radiator and cut just enough insulation off it to keep the wire straight, yet insulated to the point where it just will touch the radiator and cut the wire 1/2" longer than that. Insert the bare end of the 12ga wire into the hole and solder it there, being careful to not scorch or burn the insulation on the wire. Now solder the cap on the top of the reflector to make it 19" as in the article. I chose to use most of the remaining copper tube as a mount tube, cut so the whole antenna is 7' long overall which will allow its use inside a normal 8' ceiling room, if desired, and soldered a 3/4" female junction on the bottom of that to allow it to be screwed onto a standard 3/4" pipe nipple which can in turn be screwed into a flange which is screwed to a floor or wall (with an elbow). Once everything has cooled, carefully coat the point where the SO-239 meets the cap with silicone. Let it all set up overnight, and you're good to go.
The SWR readings on 2m and 70cm are even better than the original readings in the article.

 
The SIMPLE 2m Copper 'J' Antenna  
by N6JSX on May 3, 2003 Mail this to a friend!
I've been messing around with my J design making a version of it for my car. I found an improvement that can be made on the copper pipe J SO-239 & brass rod connections.

Flip it around so that the SO-239 is soldered to the main element and the brass rod solders to the 19" matching element. This improved my 440 band VSWR.

Also I found a more optimal placement dimension instead of 3.75" put it at 3.5".

I've received numerious "thank you's" from many many HAMs that have built this "SIMPLE" J antenna. They love it and it operates better than a comperable store bought. I'm working on a new article for making a dual band J for your car. I'm now testing it and it works fantastic increased my vehicle range by ~30 miles from a dual band mag mount!
 
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