CHEAP AND EASY: The KI6SN Porta-Mast
The ARS Sojourner
Earlier this year, during a particularly busy period at my office, time set aside to ponder, design and build a mast for portable operation went up in smoke. Ah, the best laid plans. . .
A contest weekend was fast approaching, and I wanted to operate from the field. My prime location was above the tree line on a local mountain, so some sort of support for a 40-meter wire antenna was needed.
With time running out my thinking went into "triage" mode. Was there anything existing in my radio shack that could be cobbled together or modified to meet the need?
About the only thing lying around with any potential was a knapsack full of antenna parts used in a recent Top of the World VHF contest. I'd made antennas for 2-meter and 440 MHz, with small portable masts for each. The masts for these antennas were identical: two lengths of 3/4-inch PVC - one 3-feet long; the other 4-feet long. "Hmmmm," I thought. "The two masts combined total 14-feet. Not bad."
Each of the VHF antenna masts had been guyed at the 4-foot height using a piece of plastic about 4-inches-square. A 1-inch-diameter hole in the center of the plastic slipped over the mast, and three 1/2-inch diameter holes were drilled about 120-degrees apart around that center hole. Guy strings were threaded through the 1/2-inch holes and stretched out to ground stakes to hold up the mast.
By combining the two 7-foot masts with an in-line 3/4-inch PVC coupler I'd have a 14-foot mast that could nicely support a 40-meter inverted V.
By placing the plastic guy pieces at the 7-foot and 11-foot mast heights (where in-line couplers were already in place), there would be plenty of guying to keep the mast up and running.
Completing the configuration was a 3/4-inch "T"-section at the very top of the mast. Threading a string through the horizontal part of the "T" created a pseudo-pulley for hoisting the center of my inverted V dipole.
This antenna support is very light (the whole thing weighs less than two pounds), and portable (it fits nicely into my standard-sized knapsack, although the 4-foot sections of PVC do protrude from the top).
Since the mast is guyed at two heights, and there are three guy strings at each level, there is a lot of string to sort out to assure the mast stays up. But it's worth it. Despite the mast's seeming fragility and tendency to bend, carefully placing the guy strings, and properly adjusting the tension results in a sturdy and straight-as-an-arrow antenna support.
Ten-foot sections of 3/4-inch PVC, in-line couplers and the top "T" section are readily available from your local hardware store. I used pieces of scrap plastic for the guying pieces - wood would work fine, too. Light rope or heavy twine, of course, are found just about everywhere. So, in theory anyway, all of the parts for this mast can be gathered in one trip to your local home center.
There's nothing, of course, preventing you from hoisting a 30-, 20-, 17-, 15, 12-, or 10-meter inverted V on this mast. Let your imagination run wild.
How'd I do in the contest? Well, I didn't win any certificates, but managed to work just about everyone I heard, and the antenna tuned up beautifully.
Here's a mast I'm sure is going to be getting a lot more work in the field in the near future - for sure.
MATERIALS:
(2) 4-foot sections of 3/4-inch PVC (2) 3-foot sections of 3/4-inch PVC (3) 3/4-inch in-line PVC couplers (1) 3/4-inch PVC "T" joint (2) 4X4-inch squares of plastic or light wood (with a 1-inch-diamter hole in the middle; and three 1/2-inch holes drilled about 120-degrees apart and space about an inch from the 1-inch diameter hole in the center) (1) 100-foot roll of light rope or heavy twine.
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Richard Fisher, KI6SN, a novice outdoorsman, avid QRPer, builder and operator, is executive editor of The ARS Sojourner living in Riverside, CA.