This project came about after I saw an item in
the November 2011 issue of QST. A ham from Spain, Pedro Motilla, EA5BFT, wrote
an item in the “Hints and Kinks” column about a new way to assemble that old standby, the ¼ wave groundplane antenna.
I take no credit for this design. Pedro has made a real improvement on the old design and he deserves all the credit. His
design changes make this an easy antenna for the new ham to build and also make it easily stowable in a "GO KIT" for ARES
or other event.
Now, I have built this design of antenna several
times before, but they always had the same problem. When they are completed, there is no way to store them efficiently without
bending the radials or taking up a lot of mostly empty space. Pedro’s solution is elegant and simple. He suggests using
the fittings and screws from a European style tie strip to bolt the radials and radiating element on, rather than soldering
them. That way the elements can be unfastened and stored along with the SO-239 hub in a very small space.
Since I use dual-band radios in most of my ham
radio adventures, I decided to build two antennas this way, one for 2 meters and one for 70 centimeters. The only snag in
the assembing of the hubs was that the fitting on the center conductor of the SO-239 did not want to snug up as I wanted it
to. I solved the problem by compressing the assembly between the jaws of a "Panavice" while I tightened the bolt. This technique
worked very well. You might have to file the center conductor of the SO-239 a bit as well, particularly if it has been soldered
before.
To hold them up I fashioned a “Tee” out of ¾” PVC pipe and tee fittings as shown in the diagram and the
photos on this page. Both antennas were trimmed to present a good SWR and a diplexer that I had on hand was added to allow
just one coax run down the mast to the radio. Actually, the unit I had on hand is a "triplexer" with a third port for an HF antenna.
I checked with the manufacturer and was assured the third port would not cause any problems. I capped the HF port with a plastic
cap so it would not accidentally get hooked up and their advice has proven correct. I realize that there are plenty of dual-band
antenna designs available, but since I had all the parts on hand this arrangement would cost me virtually nothing.
After I had assembled the entire project, I painted the flange of the 440 antenna red and added a strip of red tape to the
coax jumpers that connected to that antenna. This was done to hopefully avoid assembling the 2 meter antenna to the 70 centimeter
side of the diplexer and vice-versa.
The project has lived up to all of my expectations.
While not a gain antenna design, placing the assembly on top of a 22 foot mast gives me all the range I need for my assignments
for ARES or public service type events. When the event is over, all the parts store in or on the PVC frame and make a small
package that stores easily. I will add a photo of the assembly in use just as soon as the weather improves. My thanks
to Pedro, EA5BFT for an excellent update to an old design.
