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.
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.
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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HI read your comment on 5/8 wave, I strongly suggest you undertake some real
"field" trips with real tests and put your computer away. . Here is what you will find using a single 5/8 local signal will be much stronger. Distant fringe signals will be somewhat stronger. I have never found a stub stacking 5/8 or 1/2 . arrangement working without it adding a rather large Horizontal component to the pattern. Try it set up say 4 mobiles at various distances
or measure out repeater distances and use them Use a 1/4 ground plane as your
reference antenna and measure out your S meter into micro volts. By the way a 5/8
radiator can be easily matched with a gamma rod. no coil tapping required. Like the hams know 5/8 lowers the take off angle over a 1/2 or 1/4 wave. add the radials and no Choke coil required.
sorry, my saying OH "NO" Another J pole..
Hi Stan and thanks for the comment. I have no doubt what you witnessed, but that says more about your entire installation, not just the antenna. The physics involved doesn't change. As 5/8 wave antennas go, unfortunately "what hams know" is often not so.