The 11 Meter CB Radio J-Pole Antenna
Big antenna, big signal! At almost twenty-five feet tall this is one monster of an antenna!
This 11 meter j-pole antenna has a little more gain than the ordinary half-wave end fed vertical or vertical dipole and can help increase your signal strength. The antenna is a colinear phased half-wave length over a quarter-wave length that does not use radials. The design is simple and the antenna is easy to make. The tricky part may be getting it up in the air.
The lower quarter-wave section of the antenna is made with 300 ohm twin lead cable and the half-wave length top section is made with aluminum tubing. You may also substitute copper or aluminum wire for the aluminum tubing. If you make the antenna with wire then you will need a supporting structure or tree branch that is at least 30' to 35' high.
The dimensions shown in the diagram are how I built the antenna. Originally these lengths were longer but this is the size that I came up with after tuning the antenna. I believe that further experimentation would be a good idea but this antenna ended up with an SWR of 1.0 in the center of the band and 1.2 at the edges.
To feed the antenna I used a short length of 50 ohm RG-8X (Mini 8) coaxial cable. This smaller cable, as well as RG-58, is easier to solder to the twin lead cable than the larger RG-8 cable. If you use RG-58 then you may wish to use the type cable that has a stranded center for more strength. Taping the feed-point with electrical tape will also strengthen the connection.
After experimenting with the feed-point location I ended up connecting the coaxial cable to the twin lead 6" (15.2 cm) from the bottom of the antenna. Moving the feed-point location either up or down along the twin lead cable is how the antenna is matched to a 50 ohm input.
The top section is 17' 2" (5.232 m) long plus the connection to the twin lead cable adds about another half inch (13 mm). You may also experiment with a top section length that is two inches longer if you desire. Again, this antenna did come out shorter than expected.
Video Instructions Watch the video below to learn how to make this antenna.
I also expected the twin lead section to be 103" which is half of the top section length but instead it is about ten percent shorter. I ended up with a length of 7' 7" plus an extra 2" to make the end connections. The total length of twin lead cable needed is 7' 9" (2.362 m).
The twin lead cable that I purchased from a hardware store for this project is a better quality cable than what you would find for sale at your local discount store.
Tuning the Antenna and the Finishing Touches
If the antenna is built as demonstrated in the video then no tuning should be necessary. However my first antenna with about the same calculated dimensions did need some tuning. Adjusting only the top section did not change the antenna's resonate frequency. Instead I had to trim a small portion of the twin lead cable on the short side of the antenna. This part of the antenna should only be trimmed 1/8" to 3/16" (3 - 5 mm) at a time. If too much is trimmed off the short side of the antenna then you will need to make a new quarter-wave section. If your SWR match is extremely high then check to see if the twin lead has broke off at the base of the top section.
Once the antenna has been tested then wrap some additional electrical tape around the base of the aluminum tubing and top of twin lead for added support. Also tape the coaxial cable to the base of the PVC pipe or to your mast to prevent additional wear on the twin lead cable. You may also add a 1/2" cap to the top section of aluminum tubing or stuff some Coax-Seal or caulking inside of it for weather proofing.
Position an 8' long piece of wood inside the PVC pipe for use as a stiffener and secure with screws. This will add strength to the PVC pipe. Mount the wood about a foot or more below the top connection and use care not to damage the twin lead cable. You may also use a larger size PVC pipe and a wood hand rail inside for support (or just use the wood hand rail). Tip: Fit pieces together at the home improvement store before buying.
Also, it may be a good idea to attach the 1-1/2" PVC pipe coupler with 1/2" (7 mm) screws instead of using glue to hold it in place in case of future need of access.
#6 Ring, crimp-on connecter, red (insulation removed).
1/2" cap (for aluminum tubing top section).
1-1/2" PVC pipe (or wood post), 9' to 10' (3 m).
1" PVC pipe, 12" (30.5 cm) long.
1-1/2" to 1" PVC pipe adapter.
1-1/2" PVC pipe coupler.
Wood stiffener, 8' long, and screws (see end of video).
Mast (optional, but best mounted as high as possible).
Comments: Hello , My name is David and I wanted to thank you for your post on you tube and your page about building the Jpole antenna. I modified your antenna for a specific purpose and it works very well. Now reaching retirement I go camping a lot and I made my j pole all out of wire. I used 1 length of 300 ohm flat lead and just cut the one side off to length for the bottom section. I feed mine at the very bottom with coax , doing this the antenna for some reason had to become longer to get a match. Total length of mine for cb is from feed to top is 26 feet 3 inches. I use a sling shot and string to put it up over tree limbs at camp sites.
Thanks again for your work.
Safety First! Please use caution and keep common sense safety rules in mind when installing an antenna. Never install antennas near power lines or in any location that would place people or pets within the near field radiation pattern of an antenna. All users understand and agree that the owner of this web site is not responsible for accidents or other mishaps that may have been caused directly or indirectly as a result of the information published on this web site and/or in any of the video presentations.