The Jungle Antenna

The Jungle Antenna AKA 292 Antenna AKA Quarterwave Groundplane is a groundplane antenna made of just a few common parts. As the nickname implies it’s designed to work in rural, woodland areas but as anyone whose played with an OE-254 can tell you, they work well almost anywhere. They’re easy to make and very effective; it’s a great piece of kit and a fantastic skill to have once you’ve built a few homebrew antennas. Here’s what it looks like according to the book:

Fig7-13

How it works:

The Groundplane antenna is sort of like a flashlight. The radiating element is the lightbulb and the “legs” being the reflector. It’s omnidirectional, meaning the radiation pattern is in a sphere. In short, it’ll create a great advantage over the rubber duck antenna on your HT and is much cheaper and easier to carry than a store-bought antenna when used with a mobile in the field. The antenna is cut to a resonant frequency, meaning it works on one specific frequency and a few just above or just below it. Keep this in mind when planning an SOI(you did read that post, right?)

936

“If you can remember 936, you can build just about any antenna”- A guy who knows a whole lot about communications, somewhere, someplace.

936/F=L(ft)

936 is the constant number, then divided by the frequency, for a fullwave antenna length in feet. But we want quarterwave for each of our radiating elements in this exercise, so divide 936/4=234. For this example, let’s use 146.52(the 2M national simplex freq).

234/146.52=1.5970515

Next we multiply this number by 12(to get the length in inches). Do not round your numbers until you get to the finished product. You’ll get errors in your calculation if you do.

1.5970515×12=19.164618, or 19.2 inches. Each piece of wire to cut will be this long.

You need one radiating element and at least three ground elements. There’s a bunch of ways to attach them, but keeping it simple, I like banana post connectors, sometimes known as cobra heads:

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The wire can be just about anything that radiates; but I like using 18AWG. Terminate the ends and insulate. Normally Cobra Heads come with BNC connectors, so pick up some BNC to UHF(SO-239/PL-259) adapters to use with common 50ohm coax. RG-8X is lossy in longer lengths and higher power, but it works and rolls up tighter than LMR-240 does. All of your field kit should be planned according to it’s footprint in your ruck.

A semi-finished product:

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Pick up three equal length sticks and make a triangle; this forms the bottom of the antenna. Once attached, it looks like this:

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Pull it up in a tree, and you’re good to go. From a tiny hooch like this:

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You can communicate(and conduct SIGINT) quite well. And everything seen here fits just fine in that ruck with plenty of room left for the kitchen sink. Where’s the antenna??

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