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VE3CYC's Wire Beam Colltitlued/rom pagf' /8 ~ = = = im:",,",,=;;, .~.. 9 . ...... " t a..• .... TOP \lIE W -- Figure 6. Top ~'iew of the switching arrwigement to achieve maximum front-to-back performance and to switch directions of the beam. Make sure ),ou don', mount the switches on any metal surface that connects to your station ground. Figure 7. Using fWO DPDT switches to simulate a 4PDT switch. Make ~;u re y OIl throw bOi/i switches in the same direction during lise. everything wa.s still working fine , I proceeded to make an identical (win of the same antenna. induding the exact same length of feedline. I used spreaders 10 keep both antennas exactly 10 feet apart. I chose that distance 00 purpose because it is roughly 0.15 wavelength on 20 meters, and 0.225 wavelength on 15 meters. This would give me a wide range of gain and maximum fror u-ro-back ratio over most of the 20 and 15 meter bands, with an input impedance of 50 ohms on 21.2 MHz and 20 ohms on 14. 15 MHz (more about this later). The two spreaders I used were made from seven feet of aluminum tubing, with hardwood dowels hammered into the ends and screws added to keep them in place, to make the total length of the spreaders 10 feet. (See Figure 2. and details A, B, C and D.) The tubing I used was only 5/8" o.d, ofsoft aluminum, which turned out to be a disaster later on-during high winds they started to bend. I corrected this by making reinforcements (see Figure 3). I would highly advise you to use a heavier wall aluminum. or a larger diameter. You could use 10 feet of tubing as long as you keep it at least some distance away from the ends of the 20 meter insulators (mine turned out 10 be 21"). In case you do not need the reinforcements shown in Figure 3, have a look at detail D. Bum the ends of the nylon ropes to prevent unravel ing. and use plastic cement on the knots to prevent them from shppmg loose in the future. Solder the wires to the feedline right away. and cover them with shrink tubing, You should wail for a few weeks of rough weather. in case the wires stretch and you have 10 make them shorter, before you solder them permanently at the ends of the dipoles and cover them with shrink tubing. I "........, ' l.1 E ~ "U E " . , . TWO CIO'Of S" " C" .S N,~.u.El m E AC" Q l"! ~ ,c...~ "" ~ , What Makes It Work? used a heat gun for my shrink tubing, but you could use a cigarette lighter. If you have trouble soldering the wires. use Acid-core solder. It docs wonders on old, co rroded wiring . Just make sure you wash all the acid residue off before covering the connecti ons wi th shrink tubing. I have also used silicon rubber to seal off and keep things in place. It might not be such a bad idea to make each leg a few inches longer than I have specified. You can then adj ust them for the lowest SWR yourself, and cut the excessive length off later on when you are completely finished . Always stan by adjusting the lowest frequency antenna fi rst. then work up from there. Each feedline, including the length of the cable used in the coaxial choke just below the antennas and the PL- 259 connectors, was 56 feet long at this point. The Big Letdown Now I was ready for my great experiment. All I had to do was hook up one reeottne. which I will call "east," to my antenna switch, hang a hunk of coil to the other feedline, and...BINGO! I should be able to wake up every ham in Europe. Boy, was I in for a disappoinlment. After spending several hours monkeying around with all kinds of combinations of inductors and wires at the end of that unused Ieedlinc 10 make its antenna act like a reflector, the best I could get was a Iront-to-back ratio of less then 6 dB . I gave up in disgust. I couldn't figure out what thc hams in those articles were bragging about. I yanked off all the wires and coils that I had previously hooked up to the end of that open fecd linc. All that work for nothing. The Supreme Beam Then. while that feedline was hanging there dangling. Europe came in like gangbusters. I could nor believe my ears. All of a sudden I had the directional gain I' ve been after all along. I rapidly hooked both feedlines up to a two-pole antenna switch. And now, by switching between east and west, I really noticed a fair amount of gai n in both directions. After tuning up on 15 meters I had the same experience. but even better, I followed this up by making a few contacts. and the response was good. They all agreed that my antenna was defi nitely perfonning like a good beam should. That sure made my day-at least I was up to something good. Now I wondered what made it tick. The first thought that came to mind was: Since the feedline had a capacity of 28 pF per foot. and I had 56 feet of it, the answer must be there. 1had about 1568 pF in series with both legs of my dipoles. (Later on in this article the feedlines will only be 54 feet long.) This could lower the resonant frequency enough to make the dipoles. which were not connected inside my antenna switch, behave like reflectors. I also realized the theory of quarter wavelengths of feedfine, or odd multiples of it. acting like impedance transfonners. For example: If you takc a piece of 50 ohm coaxial cable, and you cut off 0.25,0.75, 1.25, or 1.75. etc., times thc wavelength of that cable (using the fonnula for quarter-wave transformers or odd multiples>. you will have an impedance transformer. To put it another way: If I would hook a 25 ohm composite resistor up to one side of this cut-off piece of thai Ieedline. the other side would see 75 ohms. This also means that if I would leave one side complctely open. the other side would act like it was completely closed. This would, for all intents and purposes, connect the two halves of each set of dipoles togethe r and makc them act like refl ectors. And . of course, by carefully manipulating the length of fecdlinc, you get various degrees between completely open or closed conditions. I am nOI able 10 explain mathematically what makes this possible. All I can say is that it works. and it works quit well. I personally feel that the principles of operation are primarily based on a combination oftbe two theories I have just mentioned: the odd multiple of quartcr wavelengths, in combination with the capecuance of the fecdlinc. Some Arithmetic According to the formula for a quarter wavelength of fcedline (246/frequency in MHz x 0.66); 0.25 wavelength of RG-58/U turns out to be 137.7" for 14.15 MHz. and 9 1.8" for 21.2 MHz. This means that 1.25 wavelengths of this feedlinc for 14.1 5 MHz (S x 137.r) is 688S. and 1.75 wavelengths for 21.2 MHz (7 x 91.8") is 642.6". Now. if you look at the total length of feedline which I am using for 20 meters (54 ft. x 12), which is 648-. plus 72- as pan of the bandswitch. plus 9" around the bandswitch, you get a total (648- + 7r + 9") of729". Then, comparing it to the actual fcedfine, we are CUi (729"-688.5") by 40S on the 20 meter band. And on the 15 meter band (648" + 9" ::: 657") it differs from the actual feedline (657"-642.6") by 14.4". Bad Weat her Leading to More Improvements Now back to business. I experienced a lot of problems on windy days because of the way the IS meter dipoles were hanging below the 20 meter dipoles. They kepi moving toward and away from each otter, As a result, the SWR meter went crazy. I look the whole system down and rearranged it the way you see it in Figures 4 and 5 and details A. B. C and D. It made the Wire Beam much more stable. 34 73 Amateur Radio Today. June, 1992
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Page 1 and 2: JUNE 1992 ISSUE #381 USA $2.95 CAN
Page 3 and 4: ONG LE~ Greatly I Is" AMlSSB Signal
Page 5 and 6: THETEAM PUBLISHERIEDITOR Wayne Gree
Page 7: their PC to discover the "ell' visu
Page 10 and 11: LETTERS Dave KD8VI, Lakewood OH I j
Page 12 and 13: Number 4 onyourFeedbeclI CIII'd 8,0
Page 14 and 15: inary address is input to the devic
Page 16 and 17: make it easier to remove, you can m
Page 18 and 19: !'Unbet' 5 on yovr FeedbKk card VE3
Page 20 and 21: Figure 2. The wire beam for /5 and
Page 22 and 23: Number . on r- F..ll'Mc~ ~ Touch-To
Page 24 and 25: Pin 17 is the GT (guard time) contr
Page 26 and 27: output and charged up C I). If the
Page 28 and 29: Number 7 on your Feedback e.rd Buil
Page 30 and 31: •• ,. ,.,..,. " " .. :.~'" ,.-
Page 32 and 33: help reduce the " thump" problem. F
Page 34 and 35: You may elect to tinker with the in
Page 38 and 39: G S.',"m,,, ,.. ,""", , " Ol 'us,
Page 40 and 41: . ICOM'" R7000 SWEEl'lNG : 1300 CHA
Page 42 and 43: 73 Review by Bill Brown WB8ELK Numb
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Page 46 and 47: planned to use. This top shelf is n
Page 48 and 49: HAMSATS Number 10 on your Feedback
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Page 54 and 55: SANELLI TECHNOLOGY Sanelli Technolo
Page 56 and 57: Arv Number 13 on your Feedback card
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Page 60 and 61: SPECIAL EVENT;,m..",,"",,,..db,,k,,
Page 62 and 63: VE eeeme. Vendors need to reserve s
Page 64 and 65: QRP Number 16 on your Feedback card
Page 66 and 67: ABOVE & BE"YOND~F-- k ~" C. L Hough
Page 68 and 69: 73 INTERNATIONAL Numbet 19 011 y(U'
Page 70 and 71: TALK WITH THE KNOWLEDGEABLE PEOPLE
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Page 74 and 75: Natural Voice Playback Board Datavu
Page 76 and 77: Joe Moel/, PE., KOOV PO. Box 2508 F
Page 78 and 79: NEVER SAY DIE Continu8(/ from page
Page 80 and 81: RTTY LOOP Marc I. Leavey, M.D., WAJ
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