2 Wave J-Pole EZNEC ...

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While planning for a ham radio hike into the mountains to support the Appalachian Trail Golden Packet exercise, I asked my club members for ideas about a good portable 2 meter antenna.

One response included a link to this web page showcasing a collinear J-Pole antenna using two 5/8ths wave antenna elements.

http://home.comcast.net/~buck0/5-8thx2j.htm

As soon as I saw the site I thought, “Oh no… not another 5/8th wave antenna discovery.” However, to my surprise (and very much unlike the regular 5/8ths J-pole which does not work well at all) the two 5/8ths sections yielded a reasonably symmetrical pattern in both free-space and over real ground at a similar height. Feeding issues aside, at least this design passes the threshold of physics.

So let’s compare the relative merits of the 5/8ths collinear J-Pole by first introducing the contenders…

I added a regular J-Pole to compare each collinear design against.

The free-space simulation, below, of the buck0 design does show a high takeoff angle compared with a regular J-Pole and a double 1/2 wave collinear J-Pole often called the Super J-Pole.

Regular and Collinear 1/2 and 5/8 wave antenna patterns.

Freespace EZNEC simulations are often practical, but what we care most about is real-world, just above the Earth, simulations. Below are the same three antennas with their bases about 360 inches above real ground in EZNEC…

This is more like it. Note the collinear 5/8 wave J-Pole does, indeed, perform about as well as a regular J-Pole in these circumstances at this particular azimuth. The half-wave collinear J-Pole beats out both antennas by about 2 dB. Here is a closeup of the lobes on the right…

The buck0 5/8ths wave collinear J-Pole does perform. However, if I take the same #14 wire, use the same cool construction techniques, but make a traditional 1/2 wave collinear J-Pole with the feed-stub, a half-wave section, a quarter wave stub topped off with a final half-wave section, the antenna is a good 2 dB stronger than the double 5/8 j-pole from buck0 in over-Earth simulations at about 3 degree elevations in all directions.

Plus if you build a regular J-Pole with #14 wire you will do about as well as the more complex buck0 design.

Less wire… simpler feed… more gain… who knew.

At least the Collinear 5/8 Wave J-Pole works, but it seems clear with the admittedly simple EZNEC simulations above, your wire investment is better spent on the simple traditional 2m meter J-Pole or the Collinear 1/2 Wave (Super) J-Pole.

Have fun with your J-Pole, but don’t forget to choke off the feed-line and mounting mast RF currents.

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