EH Antennas for Ham Radio
Welcome to the Amateur Radio section of the EH Antenna website. The EH Antenna has useful applications in all areas of communications and offers many advantages to ham radio operators. It is a very small yet very high performance antenna. Its smaller size increases communications opportunities for many hams who have been restricted by a lack of space to grow antennas. How can an antenna be so small and have such high performance? The answer is that the EH Antenna is a new concept in antenna theory, and therefore does not need to follow the rules of older antenna theory.
The Hertz antenna has been around since the 1880s, and today there are an unlimited number of variations on that early concept. However, each variation is limited within the constraints of a resonant antenna. The wires may be straight or bent into various shapes, but they must be resonant, or resonated with an antenna tuner. Resonance is necessary for maximum current flow. Hertz antennas are based on the concept that current flow on a wire causes the development of a magnetic (H) field and that a changing magnetic field creates an electric (E) field. Because one field creates the other, they have a time phase difference of 90 degrees. The two fields do not become in phase and develop radiation until they have traveled a distance of about one-third of a wavelength from the wire. This is called the “far field.” When the fields have the proper phase, amplitude, and physical relationship, radiation is created.
Compare the older antennas to the EH Antenna, where the E and H fields are actually in time phase at the antenna itself. Because the two fields are very efficiently integrated, the radiation resistance is higher than that of a wire antenna. A major factor is that the elements of an EH Antenna are cylinders and have a much larger diameter than a wire. The two elements, therefore, have high capacity between the elements, which, in turn, allows the antenna to be small. This large capacity and high radiation resistance combine to provide very wide bandwidth and high efficiency. All of this comes from an antenna that may be less than 1% of a wav elength, compared to wire antennas that are 50% of a wav elength, or ¼ wav elength with radials. On this website you will find technical information that will allow you to roll your own. We hope you enjoy this information and the use of the antennas you build. There are an untold number of EH Antennas already on the air, and many more are added every day. If you choose to buy rather than build, we have provided a link to the only company that currently manufactures and sells the EH Antennas under a license agreement.
For those hams without antenna and RF experience, buying is most likely the better option. However, we have also provided some helpful hints to those hams who feel competent enough to build their own antennas or who enjoy a challenge. First, choose a diameter that is equal to or greater than those indicated in the list below. “Meters” refers to the Ham band.
80 meters: 4 inches
40 meters: 2 inches
20 meters: 1.5 inches
10 meters: 1 inch
You may use a smaller or larger diameter to achieve less or greater bandwidth, respectively. Make each of the two cylinders equal to six times the diameter, and space the cylinders the same as the diameter. This is relatively easy, but it gets harder from here. The next step is to wind a tuning coil and locate it about three diameters below the lower cylinder. This coil resonates the capacity of the cylinders. Like a Hertz antenna it is resonant. However the difference is that the antenna is a miniature dipole that is voltage fed, which allows the E and H fields to develop simultaneously. For the first try, use small wire with an enamel coating. Later you should replace it with heavier #14-gauge wire. Connect the top of the coil to the bottom of the top cylinder, and connect the bottom of the coil to the top of the bottom cylinder. Use a grid dip meter to find the resonant frequency, and then change the coil to bring it near the desired frequency. Next, connect a capacitor having a reactance of about 100 to 200 ohms to a tap on the coil about one-tenth the number of total turns above the bottom of the coil. Then connect a short piece of coax (less than five feet) to the antenna, connecting the shield to the bottom of the coil and the center conductor to the capacitor. Also connect a ground wire to the low side of the coil and to a good ground such as the power outlet safety ground in the shack.
Now it really gets interesting, so be sure you have the proper test equipment. You must adjust the tap on the coil to provide a 50-ohm match and adjust the coil by changing the top wires on the coil to bring the antenna close to the desired frequency. The desired frequency is best found by using a field strength meter and low transmitter power. It is preferable to use a signal generator for this test. A good impedance match is readily found by use of a VSWR bridge. Once this is accomplished, you must mount the antenna to simulate the final location. Connect a wire from the bottom of the coil to ground. This stabilizes the capacity of the antenna and allows final tuning and matching.
When the antenna is mounted vertically, it is a great general-coverage rag chew antenna on the low bands and a great DX antenna if the height is between one-eighth and three-eighth wavelengths above the ground. The antenna is a miniature dipole and can be mounted horizontally for high-angle radiation on the low bands.
There is a great discussion forum on Yahoo (eh-antenna.yahoogroups.com) if you need help in building or tuning your antenna.
Click here for a list of EH antennas available for amateur use. They are manufactured by FR Radio Lab in Japan, the only manufacturer that is currently licensed to manufacture EH Antennas for ham radio operators.