reetings, fellow antennaheads, from grid square EN70gd, in the heart of the American Midwest. This month, I want to tell you about my latest antenna project, which is a natural result of my ongoing flirtation with "old" technology: my End-Fed Zepp (EFZ). I recently became temporarily disenchanted with the various permutations of the CFA, that enigmatic cross between a smokestack and a tuba, whose secrets others are working diligently to reveal. In search of ideas, I fell into browsing a 1958 ARRL Handbook for antenna ideas that were a little more in my range of abilities and finances, and a little less -- dare I say it -- "experimental."
Masters of the Air
A discussion of various wire antennas included a section on the EFZ, and I was hooked. Here was a piece of technology perfected in the days before World War II, for use with radios aboard the German, rigid-frame airships called dirigibles. These "ocean liners of the air" carried upper-crust passengers across the Atlantic in a fraction of the time required for steamship passage, and reliable radio communication was an essential part of the infrastructure required to keep them operating smoothly. Of course, a static spark, or, some say, a bomb, brought that era to a fiery end at Lakehurst, New Jersey, on May 6, 1937. The antenna technology, unlike the hydrogen-filled gasbags that carried it, continues to serve its original purpose. (For an enjoyable view of the radio technology of that era, have a look at http://www.antiqueradios.com/hindenberg.shtml, for a reprint of "Radio Aboard the 'Hindenberg'", from the August, 1936 issue of Radio News.)
The trees on my property, which are practically free of flammable hydrogen, would lend themselves to supporting a 135-foot (41 m) wire at an average height of 35 feet (10 m), especially if I could feed it from one end. I inventoried my antenna materials and came up with a 500-foot spool of 14AWG, insulated, solid copper wire; various pieces of PVC pipe; several insulators designed for electric fencing, and assorted lengths of polyester rope. (For metric conversions, click here).
How Do You Feed an EFZ?
Good timing and some extra dollars gave me an opportunity to buy another important ingredient: "ladder line." At a hamfest in Indianapolis, my brother, Jim, KA9PBO, and I found one dealer of cables who had a supply of window-type ladder line on hand. I'm certainly no expert on this kind of feedline, having been born to ham radio long after coaxial cable became the norm, but this seemed like high-quality material. The conductors are 14AWG, stranded, copper-coated steel, and the insulation is heavy, dark-brown plastic. A 100-foot (30 m) roll set me back $24 USD. The conductors combine the strength of steel with the conductivity of copper. The steel makes them stiff and springy, however, and a little difficult to handle. Cut ends are stiff and sharp enough to cause a puncture wound. Be careful, and wear safety glasses when you work with this stuff. Now, if I can just find 7 million cubic feet of hydrogen...
|Photo 1:||Balanced feedline -- 14 AWG copper-coated steel, with heavy plastic coating. Graduations on tool are 1/8-inch.|
Bending in the Breeze
My antenna environment isn't as demanding as a Zeppelin's - no close proximity to explosive gases or salty, sea air - but I do have to allow for some wind-induced tree movement, and the occasional ice storm. There are several ways to deal with tree movement, but I wanted to try maintaining the correct tension with a pulley and a counterweight. For my counterweight, I chose a 2-foot-long (30 cm) section of 3-inch (8 cm), Schedule 40 PVC pipe. I glued a cap on the bottom, and anchored it with several stainless steel sheet metal screws. I drilled several 1/8th- inch holes in the cap for drainage of condensation and other moisture.
About 3 inches down from the top, I drilled a 1/2-inch (13 mm) hole clear through the pipe, and threaded in a 5-inch (13 cm) piece of 1/2-inch, threaded rod, securing it on both ends with nuts. This rod bears the weight of the pipe. I drilled a 3/8-inch hole in the center of the top cap, threaded a piece of poly rope through it, and tied the end to the threaded rod inside the pipe. This rope goes through the pulley and connects to the feedpoint insulator at the Northwest end of the wire. With the top cap only press-fit to the pipe, I can loosen it, slip it up the rope, and add or remove ballast from the pipe as needed to adjust the tension on the wire. Although I've probably just stolen this idea from somewhere, and then forgotten where, it works, and I feel pretty smug about it. I used surplus nails for ballast, scooping them in and out of the pipe until I was satisfied with the tension on the wire. With the antenna at working height, the counterweight hangs inconspicuously in the outer branches of the tree that supports the pulley rope.
|Photo 3:||Counterweight top -- Note 1/2-inch all-thread that supports weight, and cap that slips off for adjusting weight, etc.|
|Photo 4:||Counterweight nestles unobtrusively in tree. Note drainholes in bottom cap.|
The Amazing, Improvised Feedpoint Insulator
Another amazing feat of PVC engineering (I add, in all false humility) is the feedpoint insulator. This is made from a piece of 1-inch, Schedule 40 pipe. I drilled holes for the wire and support rope near the ends, and tapered them as described in "Making Antenna Insulators for Wire Antennas," by Richard Morrow, K5CNF (antenneX, Ham WorkShop), to reduce chafing of the rope and wire. Near the end that holds the antenna wire, I drilled a series of closely-spaced 1/8th-inch holes through both sides of the pipe, on the long axis. I connected the adjacent holes with a knife, and reamed the resulting slot smooth with a hacksaw blade. At a 90-degree angle to the slots, I drilled a 3/8th-inch hole through the pipe from side-to-side. More about these holes in a moment.
The ladder line slid through this slot with some resistance. I pushed a bit more than I needed through the slot, and then drove a short piece of thick walled, 3/8th-inch OD Nylon tubing through the perpendicular holes, so that it passed through a "window" in the ladder line. This "pinned" the ladder line in the insulator, preventing it from pulling out under its own weight. I trimmed the dead-end wire from the feedline just after it leaves the top of the insulator, and cut the webbing away from the remaining wire. This wire I stripped, and soldered to the antenna wire. (And me with no engineering degree whatsoever...)
|Photo 5: Feedpoint insulator -- nylon tubing keeps feedline from
||Photo 6: Closeup of Feedpoint insulator, showing slot for ladderline
and nylon "pin"
|Photo 7: Drain holes in Feedpoint Insulator keep
moisture from accumulating.
||Photo 8: Closeup of tapered hole for wire to reduce chafing in
direction of strain.
Big Plans, No Patience
The house-end of the feedline enters the shack through a piece of plywood cut to fit the window. I mounted a set of test lead terminals that happen to be spaced the same as the feeders in the ladder line. I put alligator clips on two short pieces of ladder line to connect to the output side of the tuner -- the tuner I almost used.
In honor of L. B. Cebik, W4RNL, ("Antennas, Tales and Technicals; Research and Education," CD-ROM available from the antenneX Shopping Shack Bookshelf), I had every intention of trying to tune this antenna with an old link-coupled tuner. I got this big old box in an assortment of stuff from a local ham who was moving out of town. After a couple of hours of trying to figure out two sets of coil taps, and an infinite number of capacitor settings, my patience ran out. I mounted an SO-239 on a piece of aluminum angle, put it on the inside of the panel and connected it to the terminal posts with some short clip leads. I connected a bead balun to the SO-239 and a coax jumper to the little old MFJ-941C tuner I've had for about 15 years.
|Photo 9:||"Bud" link tuner in steel cabinet|
|Photo 10:||Tuner circuit as seen from above. capacitor is "Bud" part no. JC-1556|
Photo11: Low band coil -- "Bud" Part No. ACV-1 (160 - 40M)
Photo 12: High band coil -- "Bud" part no. ACV-2
The Zepp tuned right up on 10 meters. Starting about 2230Z, July 23, 2000, I immediately made a contact with YV5DEH, Jose, in Caracas, Venezuela on 28.399MHz. The axis of the Zepp is on a Northwest/Southeast bearing -- 320/140 degrees. It makes sense that Jose would have had a good signal, since the major lobes on 10 probably follow the wire's axis closely, and South America is Southeast from here in Indiana, USA. I got a chance to limber up my Spanish (BA, Indiana University, Spanish and Portuguese, 1971). A little later, I got to exercise my Portuguese minor. I look forward to spending a little more local daylight time on 10, looking for more South American and Caribbean stations, as well as Asians and Pacific islanders off the other end.
I tuned down through the WARC bands for a while, and stopped on 20M. In short order, I talked to AA1KS, Rick, Moose Island, Maine; PY2QA, Adrian, in Sao Paolo, Brazil; and VP2MDC, Dave, Montserrat. By 0145Z, I was in a leisurely conversation with W8LBL, Norris, West Virginia, on 40M. Norris's 500 watts kept him a steady S9 + 20-30 dB to me, and he said I was staying well above S9 on a "stingy" S-meter. On 20 and below, the Zepp seemed to be nearly omnidirectional. Not bad for barefoot on the old Icom IC-745.
Obviously, that big, old link tuner deserves more respect and attention than I gave it in this article. In the interest of time, and sticking to one main topic per article, I gave it short shrift, but I'm hoping to spend a lot more time on it in the near future. The "breadboard" arrangement of components and connections makes varying the configuration pretty straightforward, with the exception that there is not a lot of room inside for additional components, such as another variable cap. antenneX readers with ideas about how to put this tuner through its paces are welcome to get in touch with me via the link at the end of this article.
Bring up the theme music, it's time to wrap this
I'm not going to make any performance claims for this antenna, with the exception that it does act like an antenna. (I've built some dummy loads that were supposed to be antennas, so I take pleasure in the small things.) I'd be interested to see what sort of takeoff angle I get on 10 through 40, and I'll be going back to L. B. Cebik's modeling studies of Zepps for more theoretical insight. I can't give the antenna full credit for the contacts, considering the current bull market in sunspots, but obviously, it didn't hurt. I'm optimistic that the EFZ will provide me with a much-needed increase in coverage on the HF bands, and I don't have to surround myself with seven million cubic feet of hydrogen! -30- Tom Cox, KA5NEE email@example.com
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