DL6WU Yagi Design page.

Created on 7th August, 2006. --- last updated 7th August, 2006.

Here is a serious synopsis of the DL6WU yagi designs: ---------------------------------------------------------------------------------- Extract from vk-vhf mail list 7th August, 2006: Author: Graham Selwood, VK4SG: Here is some of what I've learnt about the DL6WU design...From my personal perspective. Instead of using my words, I've decided to use the words of several contributors to the VK VHF reflector. If you wish to see who said what, the text in the attachment "Identify the guilty" is colour coded to identify the author. This text relates to the history, design tools and overall concept of the DL6WU antenna and its variants......remember it's your words, not mine, and I have done my best to keep it all in context. The DL6WU ANTENNA and design tools Gunther Hoch, DL6WU spent decades on research and development of the universal antenna now commonly bearing his name. He used cut and try experimental techniques, sometimes with the aid of a large reflection free test range owned by the German Post Office. The outcome of this labour was a set of graphical curves. These can be used to design a near optimum yagi antenna for any frequency using materials which happen to be on hand, and which matches to 50 ohm coax without the need for adjustment. The DL6WU antenna provided a significant boost to VHF/UHF operators using DIY antenna systems. DL6WU has contributed to a number of amateur publications, but the first of his works to reach here appeared in VHF Communications (1977). In it he presented the basis of his recipe for yagi design, at a time before computer simulation was available. One of the reasons why the DL6WU is so easy to duplicate, is the fact that it covers quite a wide bandwidth, so any errors in boom correction make little difference to the gain. It is clear that a feature of the DL6WU designs is their insensitivity to dimensional variation. DL6WUs are not the be all and end all of Yagi's and the man never said that they were. They are very good though. It is certainly possible, without the slightest shadow of doubt, to get a little more gain for the boom length and lower side lobes than DL6WU --- however not without a considerable amount of trouble --- so for most people --- it is probably not worth it. One of the deficiencies of the design, is the first side lobe performance is only mediocre. Another slight deficiency of the DL6WU is that if you stray from the lengths of 10, 14, 19, 24 etc elements, the front to back performance deteriorates. The great thing about the DL6WU is that the design is quite wide band and pretty docile to get going, but if you try to squeeze maximum performance out the antenna (Gain, F/B ratio, side-lobes etc) then one cost will be reduced bandwidth over which the antenna has close to modelled design performance. So -- absolutely and without question -- the DL6WU designs are not a problem... The problem lies in the attempts by various people to translate DL6WUs graphs - aka - look up tables into computerized form. During the last 30 years dozens of experts have had a go at getting their names in lights by declaring that their version is an improvement over the original & the reality is that unless these optimisations have been carried out by DJ9BV or K1FO & possibly at the most one or two others [perhaps G3SEK?] I would not be taking the risk. In short some people have taken liberties with the translation from the printed graph to the computerized look up table form and falsely labelled their results as a "program" resulting in the naive acceptance of these so called programs. Most of them used formulas or lookup tables based on one of the sample Yagi designs published by DL6WU. No guarantees that they would produce numbers correct for any frequency or boom length. One of them was derived from a sample design for 1296 MHz, so if you wanted a 144 MHz yagi the program generated the 1296 design then scaled all of the dimensions by a factor of 9. Not quite the right way to do it. If you can understand computer programs you can see whether the programmer took the easy way out or did the job properly and derived his numbers from the original DL6WU graphs. But if a program is in the form of an EXE file, you can't check the code and there is no way of knowing whether it is a pig in a poke unless you do some trial runs and compare them with DL6WU's graphs. If you design and build antennas based on a faulty design tool, then you haven't really built a DL6WU antenna, and all the evaluations based on a flawed design are of little value. So to see comments about some program being the best and coming up with answers that are very close seems a bit inconsistent to me. How close is "very close" and is the difference due to representational errors or algorithmic errors? What is the definitive implementation? Are antennas built to a flawed calculator really DL6WU designs? It only takes one test case that produces significantly different results to show that computationally, they are different, and the G3SEK, VK3AUU, and VK5DJ all produce different spacing and/or length dimensions on the test case. I will leave others to argue that 20 to 30mm is insignificant in application, and that the difference in apparent computation methods is always insignificant. There seems to be a level of trust in these tools that is unwarranted. K1FO has construction software much like DL6WU however an oddball feed impedance is used which requires a special matching arrangement. DL6WU could have done this also for slightly more gain but he wanted to keep it simple. Regarding the K1FO design, I believe it was originally derived from the DL6WU design. While it seems to work well, it has lower feed impedance (22 ohms?) which has several downsides. Firstly, ohmic losses become more significant. Secondly, it requires a more complicated driven element. If you follow the ARRL design to the letter, you'll end up with sliding bars and a number of contact junctions that could cause problems later in life when the corrosion has set in. In the case of DJ9BV a 50 ohm feed impedance is retained however there is no software available to roll your own with materials on hand but if this is incorrect I would like to know where it can be found. Both of the previous alternatives have changed the design more to suit a low temperature environment & for a given boom length adds a few tenths of a db in gain. Any antenna system where lobes are in contact with warm ground, ie cannot be elevated, is not in a low temperature environment. One of the deficiencies of the DL6WU design, is the first side lobe performance is only mediocre. A better result can be obtained by putting more taper on the element lengths and also pushing the elements closer together. This can produce better than -20 db first side-lobe for a 40 plus element yagi. For most people this would still be a practical length for 70 cm. Pushed to the limit, this produces a very wide band antenna - 12.5 percent gain bandwidth at -3 db points Another slight deficiency of the DL6WU is that if you stray from the lengths of 10, 14, 19, 24 etc elements, the front to back performance deteriorates. However, this can be improved to a null by shifting the LAST director position. Incidentally, this technique works for most yagi's, much easier and more effective than playing around with reflector lengths and spacing. I drew attention to this several times umpteen years ago and times since: A, if not the major cause of back radiation in a Yagi is due to the reflected wave from the front director, that is the one way out there, returning via the string of directors to the dipole and arriving in phase with that radiation which is proceeding backwards from the dipole itself. Therefore all yagi's, note all yagi's, have back lobes which are dependent upon their length from the dipole to the foremost director. Furthermore if it can be arranged that this back radiation is in anti phase to that from the dipole you may dispense with the reflector altogether and still get a reasonable F/B. Note however that this phasing depends on the velocity of the wave along the line of directors -- which in turn depends on the total length. This fundamental fact - along with many other fundamental facts -- was pointed out at least 60 years ago So, taking all this info, and other discussion into consideration, what seems to be the consensus? Would I be correct in saying that? 1 The original set of graphical curves as published by DL6WU will produce a high gain antenna which is tolerant to manufacturing in an amateur environment 2 The Algorithms produced by Ian G3SEK and David VK3AUU Both accurately produce figures that match well with the original graphical curves 3 There has been corruption over time by persons unknown to some of the software available using these Algorithms 4 The software produced by John DrewVK5DJ is deemed to be the best source of uncorrupted software available for those not wishing to design from the original graphical curves http://www.corprit.net/~jdrew/YagiCalc.zip 5 The antennas designed by Steve K1FO, Rainer DJ9BV and David VK3AUU Have all developed further the original ideas of Gunther DJ6WU, to produce antennas which may have advantages in areas such as gain, controlled feed impedance, front to back and/or side-lobe suppression, all be it at the cost of reduced manufacturing tolerances and/or bandwidth. 6 If deviating from the lengths of 10, 14, 19, 24 etc elements in a DL6WU antenna design, some adjustment to the forward most director position may be necessary to restore the front/back ratio. To finish with a couple of quotes from the reflector: To quote a clich? why try to reinvent the wheel [unless you are very clever] when in the vast majority of cases it is not necessary to do so? Why not keep it simple, effective & risk free? The main problem with amateur antennas in this part of the world is not the design origin or boom shape but the number of them in the sky! Also for those new to the field, note that within fairly wide limits, gain is strictly a function of boom length, generally within a fraction of a db, so don't get sucked in by phoney claims of ridiculous gain from some manufacturers Read the last page of: http://g7rau.demon.co.uk/sm5bsz/antennas/cpudes01.htm It is clear that a feature of the DL6WU designs is their insensitivity to dimensional variation. Some of this goes to the issue of how much of that tolerance one consumes before drilling holes and cutting, alternatively stated as "measure twice, cut once". Having done the "measure twice" thing, I am on to drilling and cutting. BUILD IT Compiled/written by Graham Selwood VK4SG Quotes from: Ian Cowan VK1BG Owen Duffy VK1OD Gordon McDonald VK3ACC Charlie Kahwagi VK3NX Dave Smith VK3HZ Trevor Benton VK4AFL. David Tanner VK3AUU John Clark VK2TK John Martin VK3KWA Graham Selwood VK4SG ----------------------------------------------------------------

  • back to VK2KFJ main page