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Number 11 on your Feedback card

PVC Cubical Quad for 10 Meters

Build this $30 plumber's special!

by Wayne Mishler KG5BI

The station calling "CQ" at 28.375 MHz from Yugoslavia was out in the open and coming in

5-5. I keyed the mike and called him. There was a moment of silence. Then, in broken English, he said, "Q R Zed. Station calling. You are very weak. Please try again/'

I complied, No response.

Then I heard another local ham call him, and the YU came back to that guy with a 5-9 report.

For a moment, I sat staring at my transmitter, wondering what was wrong. Then i heard my competition say that he was using a directional antenna. Mine was adipole. I felt an antenna projeci coming on.

In the past, I had experimented with quad antennas for 2 meters, I still had the data for those antennas, which had produced considerable gain with good front-to-back ratio and workable standing wave ratio (SWR) at the fcedpoint. So 1 put pencil to paper and came up with the dimensions for a monobander for 28 MHz.

Much of the data came from the ARRL Antenna Book, 14th edition, and the book All About Cubical Quad Antennast eoauthored by William Orr W6SAI and Stuart Cowan W2LX.

Construction

For several reasons, 1 decided to use Schedule 40 PVC and wood dowels in constructing the antenna. These materials are readily available at hardware stores. They are transparent to RF, easy to work with, and resistant to weathering. (I gave the dowels that would be exposed to weather three coats of an oil-based enamel.) And the price was right. All of the materials, including antenna wire for the elements, cost about $30.

1 made the boom and mast from a single 10-foot length of I-inch PVC cut into three pieces (sec Photo A and Figure I): I-foot, 3-feet. and

6-feet long. To make the boom, I

Cubical Quad Mhz
Figure 1. Layout and dimensions of the Cubical quad.

cut the 3-foot piece in half. Using PVC cement, I glued the resulting two 18-inch pieces into opposite ends of a 1-inch PVC four-way cross fitting.

I made the mast by gluing the 1-foot and 6-foot pieces into the remaining ends of the cross fitting. The purpose of the 1-foot length of PVC at the top of the mast is to provide support for the boom. Nylon string connected from the top of that piece to the spreaders helps keep the boom from bending downward.

To keep the bottom of the PVC mast from collapsing when clamped into a rotor, and to provide vertical rigidity for the mast. I inserted 1-inch dowels all the way through the mast, cross fitting, and top support piece,

At first, the dowels were slightly too big to go into the PVC. A j)ower sander solved this problem,

Next, I drilled a hole in the center of the top of a 1-inch PVC cap fitting and installed a 3/16* x 2-1/2'* eyebok to serve as a tie-poi nt for the nylon string that would support the ends of the boom. I then glued this cap onto the J-foot support piece at the top of the mast.

Spreader Supports

PVC fittings hold the spreader arms (see Photo B), Both spreader supports are made the same way. Begin with a 1-inch PVC coupler fitting. Using PVC cement, glue a reduction adapter for 1 /2-inch PVC pipe into the coupler. Then glue a short (1-1/2-inch) length of pipe into the adapter. Glue a cross fitting onto the exposed end of this pipe. Next, glue another short length of pipe into the opposite end of the cross fitting. Finally, glue the base of a fitting onto the exposed end of this pipe and immediately rotate the 4'T" fitting until it is at right angles with the cross fitting when viewed from the end. With this last step, youTt have to work fast, because the glue sets up quick-

Fhoto A. The flexible PVC cubical quad has withstood thunder storms and 60 mph winds.

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