High-frequency communications (3-30 MHz) require large antennas. Multiple antenna lengths and/or tuning capability also are needed in order to change bands or use different channels (frequencies) in the same band.  In the world of HF, the ability to change bands or channels within a band is a necessity because no one frequency can be used to reliably communicate from Point A to Point B at all times.  As myriad factors change—e.g., day transitioning to night, the eruption of sunspots—one must choose appropriate bands (frequencies) to ensure a reliable working path for long- or short-range communications. Consequently, 50-130 feet of space is needed for the HF antenna.

The directivity of HF antennas is another concern.  In some circumstances, directivity is altered in order to null out interference; however, the desired stations that you want to communicate with occasionally fall in this same null pattern.  Also, when using a horizontal dipole, you will have main lobes perpendicular to the direction of the antenna lines, and no signal toward the end of the lines.  Conversely, if you are using a vertical antenna, then you will have a good signal going toward the horizon in all directions, but little signal going straight up for close-range communications that bounce off the ionosphere—a propagation method known as Near Vertical Incidence Skyway, or NVIS.

If you designed a perfect antenna, it would be an isotropic radiator with no nulls; it also would be able to work on multiple bands and have a wide bandwidth, so that antenna changes would be unnecessary as you change channels or bands.  It would be compact in size (4-feet tall x 4-feet long x 1-foot wide) and not disturbed by metal or structures in close proximity to the antenna.  Additionally, it would have a natural immunity to noise and other manmade interference.

In other words, you would have the EH antenna manufactured by Madison, Miss.-based Alpha Cognetics. Recently, we were hired by its inventor, Ted Hart, to evaluate the antenna and determine its radiation pattern. Here’s what we discovered.