How To Construct a J-Pole Antenna for the 70cm Ham Band

Here is a cost-effective J-pole antenna that is very easy to construct. In regarding a hrs time, as well as concerning $10 well worth of materials, you can have a wonderful executing omnidirectional j-pole antenna. This antenna is based on the same concepts as my 2 Meter J-Pole building plans. The j-pole antenna is essentially an end fed fifty percent wave dipole that makes use of a 1/4 wave shorted matching stub as an insusceptibility transformer. The j-pole antenna will certainly yield somewhat less than 3 DB of gain omnidirectional.

The material I picked to develop the j-pole antenna was 1/2 inch copper pipeline used for plumbing. Right here are the strategies:

The above measurements for the J-pole are in inches, as well as aren't normal for a 440 mHz. J-pole antenna. This is what it took for me to get the SWR low. Dimensions on general length, and stub size are from the centerline of the separation pipeline (straight) to the top of the antenna. The Link at measurement is 1 1/2 inches from the top of the horizontal participant to the point of link. The range between the primary component of the j-pole centerline and the adjusting stub centerline is 0.75 ″.

I cut a size of RG-8X foam coax to a size of 67 ″ for the feedline, and also coil up 4 turns (as small as you can get it) just listed below the horizontal part of the matching area. This will certainly de-couple the feedline from the j-pole antenna, and also help supply some lightning security. Connect the facility conductor of the coax to the main element, and also the shield to the tuning stub of the j-pole. To Accomplish this measurement, I use a 1/2 ″ pipe Tee, and also a "Steet Arm joint". Prior to constructing them with each other, I cut off the exess pipe at the joint before assembly.

I temporarily affix the coax making use of 1 inch tube clamps, and adjust the coax link first to the most affordable SWR. From there, I adjust the length of the major element of the J-pole. After that I start over by re-adjusting the coax connection.

The factor where the adjusting stub connects to the major element is the j-pole antenna's ground factor. That is why you can make it any kind of length. Its an excellent idea to offer a ground below. This too will certainly help with lightning security. (offered your tower is appropriately grounded!) Just usage rosin-core solder. Do not make use of "plumbing solder", acid-core solder, or pipes paste. The acid in these materials breaks down the solder joint when electrical present go through it.

Here is a photo of a 70 centimeters j-pole antenna that I use:

This has been up for concerning 7 years. You can see how the pipe transforms black from the weather. This is normal, as well as doesn't injure the performance of the antenna at all.