End-Fed Halfwave Antennas:
Do they need grounds or counterpoises, or not?
End-Fed Halfwave Antennas (EFHA’s) seem to be experiencing a bit of a moment right now and we’ve heard questions about the need or desirability of grounds or counterpoise wires when using them. Even the manufacturers of pre-made EFHA’s give mixed answers about counterpoises or not counterpoises. My unmixed answer: Yes, they do need counterpoises!
The long answer:
1. EFHA’s are a special case of “random wire” antennas. Keep in mind that an EFHA is a random wire antenna on any band other than the one it was cut for.
2. Other than loops, all antennas are dipoles whether you intend them to be or not. All antennas require some return path for the RF current to the antenna to get back to the transmitter. In a balanced center-fed dipole or a loop this is inherent. That’s why you don’t need a ground connection or counterpoise when using a balanced antenna except for static/lightning purposes. When using unbalanced, end-fed antennas like mobile whips, verticals, random wires, rubber ducks and EFHA’s, we need some form of a return path (the “other half of the dipole”). With mobile whips you have the car body. Verticals use radial arms or wires or ground screens. Or even a salt marsh. HT’s with rubber ducks use you as the counterpoise unless you provide a wire counterpoise (a very effective trick called a tiger tail. Look it up.)
3. Some manufacturers of EFHA’s advertise that you don’t need a ground or a counterpoise. Not true. You’re “getting” one. It’s a random and uncontrolled counterpoise: It’s the outside of your coax shield. If you’re lucky your coax feedline is the correct length to act as the counterpoise for that band. If not, you get very variable tuning, poor performance, local noise and, if you’re very unlucky, RF burns from your equipment. (Ask Ron, WA3VEE, about that one when he was helping someone sort out their EFHA.)
4. EFHA’s are generally used in “compromise” situations and most us deal with those! EFHA’s can be draped low-to-high and high-to-low or draped through a tree in a park. Whatever. If the end with the feed point transformer or network happens to be on or inches from the ground, you could connect the ground screw or coax connector shell to a ground rod or screen. Otherwise connect one or more insulated wires to that ground terminal on the feedpoint box. The wires should be anywhere from a tenth to a quarter of a wavelength long at the frequencies of interest. Stretch them out as straight as you can. Do not electrically connect the free end(s) to anything. Tape them up. These wires will help to isolate the coax from the antenna and should give you a much more efficient antenna.
“Should.” There are no guarantees with an EFHA. An end-fed antenna can be a bit unpredictable but it can work. If it gets you on the air, go work some stations and have fun!
Article submitted by Chuck
W3GMS REPEATER in Parkesburg, PA 