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The End Fed Antenna: Killer or Compromise?
This article is of a "homebrew" nature which includes a "review" of my experience using a 10-40m HEARC (Honolulu Emergency ARC) end fed matchbox antenna installed in a unique way from an RV park. I say unique because it was about the only way I could do it without everyone seeing it! The HEARC matchbox antennas are assembled by volunteer member hams and sold world-wide. You can buy the assembled antenna or their kit and put it together yourself (see pdf download below). The dipole is probably the simplest antenna to make and install. I'm not a fan of dipoles even if they are efficient (I like the venerable G5RV and have used them for over 25 years). An end fed aerial is a dipole but terminated on an end making them very easy to install. You can mount them horizontal, vertical, sloping, as a half square or even an Inverted L. I must admit I never heard of end fed antennas until only a few years ago. It was time I got smart on them. End feds are a single wire, full length half wave monoband or multi-band dipoles, operating without any radials or grounding. This simple aerial has been forgotten over the years in part I suppose due to the 9:1 balun which may be confusing to some hams. Hams claim end feds are; noisy, they cause interference and a good earth ground and an ATU is required. Well, I agree partially but not that they are noisy and an earth ground is required. Granted the ground is smart to have but sometimes on my portable trips that just isn't easy to do. I mean how do you get a ground on a glacier, or drive a ground rod when it's 40 below? Today you can buy an end fed from MFJ, LNR, Saga, HEARC and many others advertising on the internet. I purchased a preassembled 10-40 meter end fed antenna ($49.00 shipping included to USA-2013 price) handling 100 w from HEARC while my friend Bob K5YB got their kit. Bob said it was a piece of cake to build. So there you go, build a monobander or a multi-band matchbox end fed aerial or be lazy like me and have someone do it for you! Here's what I got off the internet while searching for end fed antennas. There are two main benefits in using an end fed half wave antenna over a coax fed half wave dipole. The main benefit is that the antenna feed impedance is around 2500 ohms and very little RF current flows into the RF earth or counterpoise. In many applications the coax feed to the antenna matching unit will act as an efficient counterpoise. If used as a vertical antenna then it doesn't need an extensive set of earth radials to be efficient. The second benefit is that the point of maximum radiation is half way along the antenna. If the antenna wire is suspended vertically from say a tree or pole then with the 20m version the point of maximum radiation is 5m above ground level usually well above local ground level without having to run earth radials. Again the point of maximum radiation is half way along the antenna wire giving some isolation from RF interference carried on the building's electrical power source. Let's see what others are saying about end fed antennas: N2CX says..Hams in general, and QRPers in particular, are always on a quest to find the "ultimate" antenna. Of course there is no single skywire that fills every ham's needs, but there is one type that belongs in the casual portable QRPer's bag-o-tricks. What I'm talking about is a classic historical aerial, the End-Fed Half-Wave Antenna (or EFHWA, pronounced "EFF-WAA"). It is extremely simple to build, erect and use. In spite of its simplicity the EFHWA has the benefit of giving repeatable, efficient and effective performance. The total overall length of the EFHWA is an electrical half-wavelength, calculated from the formula L (Ft) = 468/F (MHz) where L is the overall wire length in feet and F is the desired operating frequency in Megahertz. This is the length of wire right from the tuner terminal to the insulator at the far end. The formula is approximate, taking into consideration the "end" effect which makes the antenna shorter than a half-wavelength in free space. Extreme accuracy isn't necessary, since even the simplest tuner will make up for inaccuracies of five percent or so. Additionally, a wire that is any multiple of a half-wavelength has the same impedance characteristics; for example, a wire cut for 40 meters will also be useful on 20, 15 and 10 meters with a suitable tuner. Mine works quite well on the WARC bands too!. The EFHWA needs a ground connection, but it does not need to be very extensive. The ground or counterpoise connection simply acts to decouple the tuner and rig from the antenna system by providing a path for ground current to flow. A quarter-wavelength wire, which is half the antenna length, laid out along the ground or tucked out of the way is usually sufficient. Outdoors either the counterpoise or a short jumper connected to a large metallic structure such as an automobile or camper also works fairly well. When one end of the antenna is indoors, such as in a motel room, a heater radiator or air conditioner can be pressed into service. Try whatever ground you have to see if it works. W8JI says...End-fed antennas are increasingly popular again, at least partly because of compact iron toroid cores. Small soft-iron cores allow compact, easy-to-build, low-power transformers and networks. The combination of lightweight compact matching systems, combined with the installation convince, visual appeal, and installation simplicity of NOT hanging a heavy coaxial feeder from a long span of thin antenna wire, has rekindled interest in end-fed half-wave antennas. Unfortunately end-fed antennas have also come back with a little misconception. One commonly repeated myth or "theory" is that half-wave antennas, being resonant, do not require acounterpoise. Lack of a proper counterpoise does not mean the antenna will be worthless and not make contacts, it simply means something else replaces the missing counterpoise area. The feed line, as well as everything connected to and surrounding the feed line, become part of the radiating system. This creates three potential problems: 1.) The feed line, mast, and things around the feed line connect into the receiver. This brings noise into the receiver. 2.) The feed line, mast, and things around the feed line become part of the radiator. This brings voltage (electric fields) and current (magnetic fields) directly into the shack. 3.) The feed line and grounding affects SWR and tuning. Transmitter power levels, feed line length and routing, and the susceptibility of equipment to RF problems greatly influence things we most likely notice. This is why some people (usually with QRP power levels) swear by end-fed half-waves, while others (usually with higher power) avoid end-fed antennas. The reason for that is simple, end-fed half waves have common mode feed line current problems affecting their performance, and these common mode currents cause inconsistency in user satisfaction. End-fed half wave antennas are best for temporary antennas using low power and batteries, far from power mains and noise sources. They are more prone for problems near noise sources or consumer gear, and can easily exceed FCC RF exposure limits with surprising low power levels.
In nearly all cases, if we notice it or not, an inadequate counterpoise hurts antenna pattern and efficiency. This is why high power stations often have more efficient, more ideal, antenna systems. Higher power very often excludes use of power wasting systems, because the wasted power often creates significant local problems. If 5 percent of 10 watts is exciting the desk with RF, it isn't any big deal. If 5 percent of 1500 watts excites the desk with RF, the result can be hazardous. See attached pdf files for more info on the end fed matchbox antennas. What do I have to say about my end fed? I'll let my KL7JR/K7ICE log talk (Sept. 2- Nov. 2, 2013. States excluded except Alaska but I worked 45!). ALASKA 10, 15 & 20 ALBERTA 10, 15 & 20 ALAND ISLAND 10 ARUBA 10, 15 & 20 AZORES 10, 15 AUSTRIA 17, 20 ARGENTINA 10, 15 BARBADOS 17 BELGIUM 15, 20 BONAIRE 10, 20 BOSNIA-HERTZ. 15, 20 BRAZIL 10, 15 & 20 BULGARIA 17 BRITISH COLUMBIA 15, 20 CAPE VERDE 15 CANARY ISL. 20 CHILE 10 CUBA 20 COLOMBIA 10, 15 CURACAO 15, 20 CORSICA 10 CZECH REP. 15, 20 CROATIA 10, 15 & 20 COSTA RICA 10, 20 ENGLAND 15, 17 ESTONIA 10, 15 ECUADOR 15 FRANCE 10, 12, 15, 17 & 20 FINLAND 15 GRENADA 10 GUATEMALA 10, 12 GERMANY 10, 12, 15, 20 HAWAII 10 HUNGARY 10, 15 ISLE OF MAN 17 ITALY 10, 12, 15, 17, 20 IRELAND 20 ICELAND 15 LUXEMBOURG 20 LITHUANIA 12 MEXICO 10, 15 & 20 MANITOBA 15, 20 MOROCCO 20 MADIERA ISLAND 12, 15 NEW BRUNSWICK 20 NOVA SCOTIA 17, 20 ONTARIO 20 POLAND 10, 15 & 20 PUERTO RICO 10, 20 PORTUGAL 10, 20 PERU 15 QUEBEC 15 RUSSIA 15 SASKATCHEWAN 10, 15 & 20 SABA 10 SCOTLAND 15 ST. LUCIA 10 SLOVAK REP 10 SERBIA 15, 20 SWITZERLAND 15, 20 SPAIN 10, 12, 15, 17& 20 SLOVENIA 10, 12, 15, 17 & 20 TRINIDAD & TOBAGGO 15 TURKS & CAICOS 15 UKRAINE 15 URUGUAY 10 US VIRGIN ISLANDS 10 VENEZUELA 17 WALES 10 YUKON 10
What antenna??? As you can see, the matchbox aerial is quite stealthy. I doubt any one knows what I'm doing in the RV campground! The bottom of the matchbox coax connection is about 4 feet above the roof and then vertical section goes about 10 feet as a sloper then levels off and zig-zags horizontally through the tree branches 5-10 feet above the roof. Antenna comes with 30 feet of wire and by experimenting; I added about 15 feet to get a better match on 40m. Earlier on I mentioned I didn't much care for dipoles, and what I've experienced with this wire aerial only about 20 feet high has me totally dumbfounded especially because I have no ground radial system nor is my rig even grounded! Later on I will try this aerial as a vertical, but for now I'm having too much fun! You decide if it's killer or compromise. I already have and will order another matchbox soon! 73 de Yukon John in South Carolina UPDATE - Operating from Dominican Republic 07-2014 The 45 ft long End Fed is up about 20 feet and mostly horizontal. The Inverted L is up 40 feet and about 55 feet long with 3 long ground radials.
On 10-20m the End Fed consistently out performs the Inverted L by 2 to 4 "S" units. The Inverted L will stay up for 40 and 80m use.
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