More DDA Matching Networks
Introduction
This magazine’s content presents a great deal of eXperimenting and eXperimental projects. Wouldn’t it be wonderful to read originals or copies of the daily Journals collecting the personal notes of inventors the likes of Marconi, Bell, Edison, Tesla, Yagi, etc., describing the step-by-step process of trials of the experiments that led to some of their now famous inventions? I believe you would agree. Although this magazine doesn’t dare to compare itself and its projects to the level of importance of those produced by such geniuses, this Journal does provide a record of our current-day projects, like with the DDA. And who really knows where an invention will lead or what other inventions it will inspire from having created a vein of thought? We know what our objectives are for this little antenna device, but we are far from entirely understanding how it works and what its limits may prove to show. Articles like those we have been producing about the DDA or any other new project, allows you the reader to either observe and vicariously experience the process of inventing—or, better yet, jump in and try some of them yourself. Yes, we will include some of the more important failures, which will normally outweigh the successes, so you the reader can avoid going down some of the same wrong paths. We learn from failures. Can you imagine how many things Edison must have tried before succeeding with the light bulb? Somewhere, I vaguely remember he tried hundreds, if not thousands of materials for the right filament. When asked, during the experimenting, if that didn’t discourage him, he merely replied, “no, at least now I know of those things that don’t work!” ~ Jack L. Stone, Publisher
More Network Trials
During the past month, more experimentation was accomplished in optimizing the matching network for the DDA as well as for the CFA. The original network described in an earlier article has been modified improved considerably through numerous eXperiments. The current network being tested is an interesting one GARDS member Harold Allen, W4MMC, designed and sent in. But first, let’s review one that did not work well enough to stay in the running.
Figure 1 shows the one just tested and measured during the past month. The main reason we don’t like it is because the network did not give enough phase shift to adequately excite the antenna. All modifications tried resulted in insufficient increases in performance to make it work well enough to stay in the running. It may work on some other antennae, but not very well for the DDA.
The latest network now being considered is shown below in Figure 2, which shows promise. A further modification of it in Figure 3 does not show much promise, in fact probably a step backwards. However, it’s part of the eXperimental process to try effect of changes.
The circuit in Figure 2 will be the subject of its designer, Harold Allen, W4MMC in next month’s issue.
Figure 4 shows another circuit already tried but with a moderate amount of success. Here again, it did not give adequate results to continue applying it to our DDA projects. The device caused overheating of the toroids as well as again producing inadequate phase shift. This was run through the mill and despite several changes, dropped from the running too.
Figure 5 shows another network circuit tried by others working on this same DDA project and it produced some results, none of which were considered adequate.
The tests that were run this past month all generated results, and no matter how small, it has encouraged us and indicates that we are on the right track and the best matching/phasing network to tune the DDA (and CFA) will be found soon. Further tests indicate it may be possible to remote-manage the network from the antenna allowing the tuning to be done from the ham shack. Also the possibility of remote tuning with motors is definitely in the works, in case the feedline experiments do not work out to our satisfaction.
Even though the time that has passed may seem excessive to many who wish to build and operate either a DDA or CFA, please keep in mind that the main objective is to arrive at a matching/phasing network that can be easily built and tuned up. Thus far, I have learned that the toroid I had been using would heat up even at 20 watts, which came as a surprise to me as it had been used previously in a 100-watt tuner! At least in my own eXperiments for now, the use of a toroid has been dropped in favor of using conventional coils. All of the coils I have used were handmade and wound, using house wiring with the insulation stripped off (see another article this month in the Ham WorkShop about how to wind these coils yourself).
Any change in configuration results in a whole new network being built from scratch and which takes time. The reason for the entirely new network is that at present I am not counting on separating the network from the antenna base. So I am trying to keep the network confined to a small size able to be fit within the area dimensions of the bottom disk of the DDA so the entire combined unit comprised of antenna and network will fit into a covering radome.
Double Your Fun
Bear in mind that the network to be derived from these experiments most likely not only be ideal for DDA, but the CFA as well. This will enable anyone to experiment with both antennas and determine which antenna configuration will be the best for a particular application.
Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF
Last Updated : 13th May 2024