Antenna Design and Construction
Over the years, I have owned and operated many of the gearmotor antennas available in the amateur radio market place. I have always been disappointed with the limiting diameter of the coil in these antennas, due to the limitations of the mast diameter where the coil resides in.
For some time, I have been working on a design that would allow me to build an antenna that circumvented this problem. After a lot of thought, I came up with a design that utilizes a coil that has two diameters, the upper working section of the coil that tunes the various bands, could be of any diameter you desired, and the lower tail section of the coil that supports the upper section, would be of a smaller diameter, along with the matching diameter mast that supports the complete antenna.
As you can see, I have built a prototype, and it is proving to be what I have always wanted in a gearmotor antenna, a antenna that is not limited by the size of the coil that can be utilized in its construction, because of the lower mast diameter required to house the coil. I built this antenna with a 3 inch coilform, proofing my design, but I also had a particular need for a antenna that did not exceed 4"OD, as I wanted to be able to store the coil/mast assembly in one of the side compartments located at the rear of my Avalanche. Still, the design is sound, and the design that I came up with is capable of utilizing a larger diameter coil with the same results.
It has been some time since I have got as much satisfaction out of one of my projects, as I have gotten from designing and building this gearmotor antenna.
Everything, from my earliest thoughts on what I had in mind for a new antenna design, to the actual designing & building of this antenna has progressed without a glitch.
With the antenna mounted on my mobile, and after very stringent testing of the antenna over a period of 6 months, and in temperatures ranging from 35 Celsius in the summer months, and down to minus 30 Celsius through the winter months, I have proven with test results that the antenna works & performs as I imagined that it could.
My gearmotor antenna with its one of a kind coil assembly is proving to be a very good design, and the 3 inch coil with the smaller diameter tail section of the coil is wonderful to see in operation. The coil is rock solid with no side to side motion, when extended in the 80 meter position, and will handle the biggest of whips with a included caphat with ease.
The design also allows the Delrin tail section to track smoothly and freely in the lower mast housing, due to the tracking keyway that is cut in the lower tail section of the coil, assuring that the coil cannot twist in the housing while being powered along its path by the gearmotor.
The gearmotor powers the coil assembly without any effort, and draws a milliamp sipping 250 milliamps under load.
Oh...did I forget to mention that the complete coil/mast assembly minus the whip, weighs in at just 6 pounds.
My antenna design from 2010 with its 4 inch coil seen here, weighs in at 11 pounds,
HF antenna installs....