The W3EDP antenna

Just to remember the old (but still good) antenna tricks, here is a brief description of the W3EDP antenna. It is included here because I worked some DX stations operating from portable sites with very strong signals. I asked “what antenna are you using” and they replied “a W3EDP”. So, I started to search what is the W3EDP and found this description: In 1936, Yardley Beers, W3AWH, described an empirically-derived antenna “designed by the writer’s friend, Mr. H. J. Siegel, W3EDP.” It consisted of an 84 foot radiator and a 17 foot “counterpoise.” The design has lasted through the years. I’ve explained elsewhere how it is related to an end-fed Zepp (a true Zepp, as once trailed from Zeppelin airships). With the indicated dimensions, the antenna works well on 40, 20, 15, and 10 meters. Like the FFD, the ‘EDP requires a tuner.

 

 

If you’re at a site calling for an end-fed antenna, the W3EDP may be the one for you. Rather than run the short wire off in an odd direction, slightly better performance results from configuring the two wires to produce an end-fed Zepp. Use three of the quick-connect spacers described above. Terminate the short wire with a top spacer at the 17 foot point along the long wire (with a couple of other spacers along the way), and run a support cord outward from the same (short-wire) end of the top spacer. This gives a 17 foot feedline with 6 inch spacing. From the other end of the top spacer, run the remaining 67 feet of the long wire outward as the flattop portion of the Zepp.

 

If you don’t configure the W3EDP as a Zepp, it is still best not to lay the short wire on the ground in the usual counterpoise fashion. This wire is part of the radiating system. If you’re not sure whether you’ll need an end-fed or a center-fed design, carry two 84 foot lengths of wire and one 17 foot length. Use the 17 foot length and one 84 foot length to whip up a W3EDP/End-Fed Zepp, or use the two 84 foot lengths for an FFD. There’s been a lot of recent interest on qrp-l in the W3EDP antenna. This is an antenna with a 84 foot wire on one side of the output port and a 17 foot wire on the other side. The 17 foot side is sometimes called a “counterpoise.”

 

Here’s my “take” on the antenna’s operation, along with a suggestion or two: To begin, the “counterpoise” isn’t a real counterpoise, or at least it doesn’t function like the usual counterpoise (except on 20 meters). The normal function of a counterpoise is to establish a point of minimum rf voltage or “ground” potential. A quarter-wave length of wire does this when the far end is open. (That’s assuming it isn’t detuned by nearby objects or by the ground itself.) Except on 20 meters, where it is approximately a quarter-wave long, the “counterpoise” part of the W3EDP antenna doesn’t fit the bill here. The best approach is to forget about the short wire as a counterpoise.

 

To understand the W3EDP, instead conceive of the short side as one side of a feedline that’s been separated or pulled apart from the other side of the feedline. Now in your mind move the short side so that it’s parallel to the first 17 feet of the long side and anywhere from several inches to a foot or so away. What you have is a section of feedline. This gives you a standard *end-fed zepp* (in other words, a true zepp antenna, as in zepplin flying), with a fundamental frequency of about 7 MHz. The flattop portion is 67 feet long, and the feedline is 17 feet long. The impedance of the feedline, which is not critical, is somewhere in the vicinity of 500-800 ohms, depending on wire diameter and spacing. An end-fed zepp will work on its fundamental frequency and on odd and even harmonic frequencies (that is, where the flattop is an odd or even multiple of a half wave). With our W3EDP-derived end-fed zepp, the antenna will work satisfactorily on 40, 20, 15, and 10 meters.

 

The principle of operation is this: At the feedline end of the half wave flattop (or multiple half wave flattop), the impedance is *very* high. The impedance at the antenna end of the *open* side of the feedline is also *very* high. (Were it not for capacitive coupling to space and various objects, the impedance at the antenna end of the open side of the feedline would be infinitely high, but in reality the current never quite falls to zero.) If the length of the flattop is properly adjusted, then the currents on the two sides of the feedline are *roughly* in balance, but out of phase, so not much radiation occurs from the feedline. (If you’re familiar with a j-pole antenna, it’s the same principle of operation. And with both the end-fed zepp and the j-pole, there’s controversy over whether they work quite as they’re alleged to.

 

But that’s another story, getting into fine points of feedline balance and what happens at the antenna end of the open side of the feedline. Also, the resonance of the flattop on harmonic frequencies isn’t exactly an odd or even multiple of the fundamental frequency, owing to differing impacts of nearby objects and of end effects. But that, too, can be put aside in understanding why the W3EDP works.) Now, if you start pulling the feedline apart, you start to get more radiation from the two sides of it. If you move the short side out of the vicinity of the long side, you don’t have a feedline effect at all and you have a W3EDP antenna. But–and this is crucial to the W3EDP design–the currents at the transmitter/tuner ends of the two wires are still roughly equal and roughly out of phase. This means that you can connect them to a link-coupled tuner without serious imbalance. And this remains true on harmonic frequencies. This also explains why, if you try to operate a “standard” W3EDP on 30 meters, you may find significant hand-capacitance effects as you try to adjust the tuner. If you follow through the foregoing analysis, you will see that there is nothing absolute about the 84 foot and 17 foot dimensions.

 

In general, what you need is a short side of x feet, and a long side of (x + y) feet, where y is a half wave at the lowest frequency. For example, you could set the two sides at 22 and 89 feet, for fundamental operation on 40 meters, and harmonic operation on 20, 15, and 10 meters. This would likely not be a good length for 15 meters, however, because the impedance at the tuner would be quite high. (Think of the input impedance of a half-wave length of feedline that’s terminated in a high impedance.) Indeed, the “standard” W3EDP is likely to have a high feedpoint impedance on 10 meters, just as in the case of an end-fed zepp fed with a half wave feedline. For 10 meters, the 22 and 89 foot dimensions would probably be better in terms of keeping the impedance at the tuner within a satisfactory range. An idea for including 30 meters in the W3EDP design is to have a second short side to switch to. With the standard 84 foot length for the long side, a short side of 38 feet should give reasonable balance on 30 meters (the rough conceptual equivalent of a 46 foot flattop and a 38 foot feeder).

 

There is one important point to keep in mind. Unless the short side is run fairly close to and parallel to lower portion of the long side, there will be significant radiation from the short side. This means that it is best *not* to have it on or close to the ground (in the fashion of the usual counterpoise). If it’s close to ground, it will be radiating into a rather lossy environment. In fact (without having modeled the different configurations for comparisons, or having done actual comparative tests), I’d say there is at least a theoretical advantage in running the short side in true “feedline” fashion, within several inches or a foot of the lower portion of the long side and roughly parallel to it. (Or get the wires close to this configuration.) The result will be more of the total radiation occurring at a greater height and thus lower near-field ground losses.

 

I’ve used a W3EDP with one of my z-matches, with no difficulty on the indicated bands. I’d imagine the W3EDP design should pose no problem with Roy Gregson’s ZM-1 or ZM-2, either, although the two output links in my design give a little more flexibility. A standard link-coupled tuner (which L.B. carefully describes on his Web site) should be fine, too. A single-ended tuner–L network, T network, etc.–requires a balun (and that may present its own problems.)

 

Charlie, W6JJZ