20 meters Cage Dipole

It was August, I was on vacation, I was away from QTH and I had no access to any resource but some hardware tools and a lot of thin wire (the kind used for telephone lines). I badly needed an antenna for 20 meters. It was when the Cage Antenna solution came to my mind. First time I had read about this kind of antenna was when I got my first Antenna Book. Cage Dipole is based on the fact that a wireframe does emulate a tubing of the same diameter, supposed that the wires in the frame are close enough to resemble a solid surface.

I had a piece of plastic tubing, diameter 60 mm., so I decided this was going to be the diamter of my wireframe. I cut three pieces out of the one I had, the first and the second piece together about the same length of the thirs one. The first and the second were going to be used as antenna ends holders, the third as central spacer.


fig. 2

I made 8 holes (fig. 1) on both the sides of the central support and on just one side of the other two (fig. 2). On those last two I made 4 more holes on the opposite side of the 8 ones, useful to hold the dipole up in the air. Then I cut 16 pieces of my telephone wire, each 5.20 meters long. The wires have been then fixed to the plastic supports passing them through the holes and tying all together like in fig. 3. The biggest problem in this phase is that, in order to assemble the thing, the antenna must be always hold in tension, to avoid the tying of the thin wires, and to make sure that the tie inside the support tubing is made so that all the cable will show the same length caming out od the holes.

fig. 3

fig. 4

Finally, I obtained two dipole legs, each made of 8 wires. now, the ends of the wires MUST be soldered together on both the sides. The soldering on the central side of the legs will be the connection point to the coaxial cable. An RF chocke coil is recommended for this antenna, building it directly out of feed coaxial cable. I used RG58, not surely because it is the best you can use but because it was the only one I had in house. Fig. 5 shows the complete work, already holding on the roof of the building.

fig. 5

Results have been really satisfactory, with the antenna showing no SWR at all, and the largest bandwidth I had ever seen. The day after the assembling I was successfully running a couple of QSO with ZL.

73 de iz2eeq