The Short Version. I'm not sure there are any list moderators that would tolerate the long version. It's a book.
If you already have a dense, uniform 160m radial system, you know what you have. If you can and are planning to have dense and uniform, stick with it. The rest of this is for you who do not have, will not have or cannot have. Reasons for not doing dense radials vary widely from too much work, to "political" difficulties with the household planning department, to confining circumstances that simply make it impossible, a whole host of compelling reasons. Hams have suffered in the confined circumstances by attempting various minimalist extrapolations of commercial radial methodology. The rub is that commercial grade research was never done on non-dense, non-uniform solutions. And why would it? If one builds an AM broadcast station, one buys property large enough to do the efficient antenna. The continuing, year in year out, now until forever, extra power bill expense of running extra power to an inefficient antenna to maintain an FCC mandated field strength, economically precludes cutting corners on the antenna system. It's a total no-brainer to spend the money for the efficient antenna solution, including the necessary property. What would we be doing if the FCC mandated that all hams on 160 meters had to maintain a specific field strength while transmitting, say the field strength of 100 watts on a commercial BC grade vertical and radial system. A poor antenna would require buying and running an amp. Some really poor installations I have seen would require a linear with 30 amp 240v service to it to match 100 watts on a commercial BC grade antenna :>) Hamdom has made considerable assumptions about extrapolation of commercial BC antennas into the world of constrained circumstances. We have been hindered on all sides coming into proper research on how these extrapolations actually work. Hindrances follow, not in any particular order: 1) Until recently, we have had no readily available way to accurately measure sky wave. Commercial AM BC is all about ground wave. Hams are all about sky wave. The Reverse Beacon Network (RBN) is about a year old. RBN is the first practical, universally available measurement device for skywave that will allow overall accurate comparison of signals from various installations. One can compare the signals of two stations graphically across a contest weekend and compare the transmitted signals of two closely located stations, to within a dB or two, as heard at locations all over the country and the world. A/B tests on an S meter at either end, either RX or TX on the antenna in question, have proven notoriously unreliable for a stack of reasons, and have led hams on occasion to discard the better working solution. The RBN network has shown 10 dB differences between two local systems here that popular opinion expects to be in the opposite relationship. Folks seem to be slow in embracing these comparisons, with not much acceptance of conclusions flowing from the comparisons. 2) The raw loss factor of dirt varies hugely. Some hams can "get away with" lossy methods because of their superior dirt. Other hams using the same installation over poor dirt have their signals sucked dry of strength like a prune. This leads to arguments about whether an antenna "works", that can't be resolved. The FCC's standard USA map plot for ground conductivity assumptions for use in AM BC station design and license applications varies from a sucky sucky 2 millisiemens all the way to an almost miraculous 30 millisiemens. If you are one of the lucky ones with 30 millisiemens dirt, you probably can get away with anything, including a configuration that would be a dummy load on 2 millisiemens dirt. The real question at root is how well your DIRT works. If you're not one of the lucky 30 millisiemens folks and you can't do dense and uniform, your first consideration about an antenna should be how to minimize induced ground loss. That seems more often to be the last thing commonly thought about. 3) Literature leads us away from the ground loss problem. It has only one solution: dense and uniform. But they're NOT telling a lie. It's true, and it's the BEST solution. You SHOULD do dense and uniform if you can (use your own personal definition of "can"). Those are the killer signals on the band. But there is just about nothing in the literature like, "How to do 160 meter vertical antennas when you can't do dense and uniform radials." This creates a huge credibility gap for those trying to push loss mitigation which in turn foments an easily discernible resistance to progress on the issue. 4) Dirt at MF is a science in it's own right. And its characteristics that pertain to radio energy absorption can vary wildly (I use this term with accuracy and conviction) from area to area, from neighborhood to neighborhood, and even in the same back yard (measurements, not speculation). If construction site leveling for house building has not turned a property into a totally miscellaneous conduction/dielectric layer cake, mother nature over the millennia may have, as at my house. My back yard is clay over sand over clay, over ancient forest fire. Out toward the service road by the creek, it's layers of acidic rotting leaves and pine straw kept damp under-surface most of the time except late summer. This numbing variability makes progress by comparison of results difficult. One's opinion of the whole thing may be skewed one way or another simply by the dirt available to those whom one has talked to for advice. 5) Instrumentation for measurement of conductivity at medium frequencies is not nicely packaged in inexpensive MFJ style boxes. This is in abject comparison to antenna analyzers, and modeling programs, which have had wonderful progress in the last decade. On the whole, we're too busy resisting the idea of starting with loss mitigation, that if substantially accepted, might generate enough demand for inexpensive conductivity testers. We have to roll our own measurements, with all the data conversion work and opportunity for error that implies. How much attention would you pay to SWR if you had to make your own SWR box to measure it? In the 50's I never paid any attention. My tiny budget for radio barely afforded TX and RX of any kind. I still worked all over the world, until I moved my multiband vertical from copper row house roofs to backyard sod and a ground pipe, and couldn't work anybody, and couldn't understand why. I'm certainly not knocking analyzers, but the demand for such instruments precedes their availability. 6) Nobody wants to think they've been "had." But hamdom, in regard to extrapolation of commercial MF vertical/radial techniques, and understanding ground losses and loss mitigation for confined circumstances, has been "had." The particulars are largely considered so mushy that the subject has largely has been reduced to a war of "opinions." The first look is not to science, but to the reputation of the author, if even that. It has become "schools of thought" when it should have been science and design. This introduces an unfortunate irritation factor to discussions, where people want to think that all opinions should be equal, and don't want their own opinion stomped on. Not that science doesn't get into heated arguments about areas where proof does not yet extend, or the "proof" itself is a controversy. 7) The math involved is really nasty. And there is controversy about some of it. Small wonder. Could anything that nasty REALLY have been proved out all the way? Some part of my gut screams "Fishy! Fishy!" every time I get into this. I do get it, there's a part of ME that remains convinced there is more than a hint of voodoo in this. Why should I NOT expect that from the hinter lands. 8) Even the high-priced, legal agreement, professional grade, USB license key, modeling programs cannot deal with the vagaries of dirt. The growing consensus is that models generally UNDER-estimate ground and miscellaneous dielectric losses. The reason is simple: noone is going to dig up and measure the conductivity of every cubic foot of their dirt to a depth of ten feet across their entire back yard. And even if you did, the high-end Norton-Sommerfield ground estimation method was written for monolithic dirt and to "calibrate" ground estimation to real field strength measurements at the ground from commercial grade installations. One confounding issue at 160m is that the water table can be visible to the RF, with the ground increasingly described by knowledgeable authors as actually semi-transparent at MF. There is simply no existing way in the current programming to deal with a VERTICAL two medium stack underfoot. What will pay for that expense and trouble? And would you ever practically have MEASURED data to drive it for use at a ham level? 9) The physical aspects of a full spread of tests, to combine both existing dense and uniform, and non-dense and uniform methods, is very difficult and requires a significant crew some number of days just to do a suite of tests on only one site with it's unique dirt structure/content data points. There is a reason why this kind of work usually gets done with research money to PAY people to travel and show up. Then there is the need to go and do exactly the same tests on different sites to get a range of data to display the rainbow of results, and see the variation on different sites with different dirt. 10) The size of a halfwave on 160 complicates matters, eliminates many sites, and creates difficult construction issues for tests. To deal with this, some have made tests on 40m, and extrapolated results to 160m. We now know that does not work well because at 40 there is more of a hard "skin effect" to the dirt which is easier and more accurately served with a monolithic ground estimate. So we have to do our experiments full size, down at 1.8 MHz, so we get understandings and solutions that work at 1.8 MHz. To run a base comparison on 160 one has to start with a dense quarter wave radial system, 120 if it's on the ground, and repeat measurements as one does harmonic reductions of the radial count. And do that BOTH for elevated and on-ground. This gives the trusted base measurements to relate to non-dense, non-uniform counterpoise solutions. This is an awful lot of work just installing, supporting and removing. Leading into number 11: 11) The variability of solutions, and the need to include them ALL on a scale of effectiveness leads to a very large matrix of tests to be run on a single site. This in turn needs a clever mechanical progression of tests to minimize the work moving from one test to the next. Many of the INDIVIDUAL tests in such a suite require construction of antenna system components that would be a fall project for many a ham, and would thereafter be what was used for a long time because that was all the spare time (and money?) available for allocation. We're talking about installing forty or fifty antenna systems, and then carefully measuring and recording them, in a few days? 12) At least so far, I have not been able to figure a procedure that would allow a crew to get through all the needed activity on a weekend of two twelve hour days. It appears to need two or maybe even three two day weekends PLUS corresponding weekends of crews. And that for only one set of data at one site. 13) The measuring protocol has to be dead on, and in the work laid out in 12) we have to NOT have a killer flaw that requires starting over with the flaw fixed. That can throw a lot of work down the toilet and be very expensive. 14) The weather needs to cooperate, and no rain and mild wind are required. Some of the tests have some matrix columns for signal sources suspended from balloons, to positively measure at angles NOT along the ground, since hams are skywave users. Multiple weekend rentals of helicopter plus pilot is not being considered. 15) Assuming the above can be worked out, the need to spread out the work over weekends might require dominating the test site between tests. This means that a meadow in a public park may be difficult to use, or require taking everything down after each "session" . 16) If one considers a paid crew of six college students for five twelve hour days at $100 per day, that's $3000 per data set NOT including food and transportation. To pull this off at a carefully selected range of ground type sites, probably scattered around the US, one is talking easily about 25-50 thousand dollars, with the difficulties of rounding up crews LOCAL to the testing sites. And from various past experience that expense could be ridiculously underestimated due to something I'm overlooking. That's the stuff required for delivering PROOF that people can bet their hard earned spare cash and time on. I get that. I really do. Bell Labs and all the radio pioneer giants have already been there, but not for the non-dense non-uniform radial-disadvantaged crowd, and not much for skywave. They all had employers who had big money skins in the game that needed the knowledge. Adjusting for current value of past expense, we're probably talking about millions of dollars spent on the original research. And even at those levels, that was money considered well spent for needed answers to questions with a lot of money hanging on them. This is why we don't have the science long in hand for hams, with MFJ and Radio Works happily manufacturing decently efficient small site 160 antennas based on those principles plus matching devices that one just dumps out of the carton, strings up, tunes up, and then goes inside to make good contest scores on 160. Just a rant on my part, folks. Maybe some of this stuff will catch on and we'll get a little tail wind. 73, Guy. _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
