I'll have to counter that the two radial figures in your quoted RCA study are not about defining what goes wrong with minimalist and miscellaneous downward extrapolation of dense and uniform radial systems. It's about setting a context for the main purpose of the study which is the superior efficiency of 120 times 0.4 wavelength radials. The study was not done to do a pathology on crap radial systems, but underline the superior worth of dense and uniform.
1) The first assumption is that 3 MHz is the same as 1.8 with essentially no radials around. It's turning out that if you're talking about non dense and non uniform, it's not the same. It's changing as you go down to a lower MF that exhibits some strange behaviors I've never seen on eighty meters. Tests for a given frequency need to be done on that frequency. BUT if you have a dense and uniform radial system you don't see the weirdness. This is an important distinction. The ASSUMPTION is that the stuff goes bad the same, but that wasn't the point of the 1937 testing. The GOOD end of the results were the point. At root of all these studies (and properly so) is their goal to pin down the point where you get MAXIMUM BENEFITS, not to carefully quantify exactly how bad you can get if you DON'T go for the best. You can see where the FCC 120 0.4 wavelength radial figure came from. Once they got that pinned down, the research party for how to do BC stations right was over. No-brainer to buy the land and put down copper in lieu of everlasting power bill penalties. 2) Sky wave behavior is ASSUMED to be the same as at the ground. This is risky because of the loss mode presumptions used with the ground based field strength. If there is growing ground transparency at the lower frequencies, and the field strength at ground is IMPROVED (absent dense radials) because of whatever unknown mechanism, then the performance of fewer radials will score TOO HIGH at the ground for extrapolation to sky wave. This is heavily suspected (not proved) on my part because it would explain so much. The proof will require burying current sensors that are self contained, battery operated and contain recording devices, running tests, and then digging them up to unload the data. Or connecting them with air-breathing testers above ground with fiber optics. These kind of ground current things could not be done in the past because the wires connecting sensors would skew the measurements, and they knew that. What is really going on in the ground is still the undiscovered country. Remember that the famed Mr. Beverage had a BURIED 500 kHz TRANSMITTING antenna at one point that worked. Dense and uniform radials do their magic by taking the ground underneath OUT of the equation, so we DON'T have to know about it. Unless we can't do dense and uniform, of course. 3) There are just too many grotesque differences as measured on RBN, even after all the various (and rightly pointed out) caveats are dealt with. And that is not a rub on this RCA study. All these studies have this blind spot, as if measurement at the ground is in it's own world and seemingly unrelated to skywave. There are often order of magnitude discrepancies with projections of the old studies and RBN readings. The 1/4 wave radial drawing shows a difference between the 2 and 60 radials as 116/176 mv or 3.6 dB. Something else in the real world can produce 20 dB differences in sky wave at far points, other factors held equal. It is a fact that putting down lots of radials cleans that up. More radials is better is no urban myth. Dense and uniform really does work the best. But two askew radials often seems to do orders of magnitude worse than such material as the RCA study would suggest. One 100w station in Minnesota went from barely working and being heard in North Carolina, to working Europe, just by picking up his two 1/4 wave radials off the ground, and folding them back elevated to the feed. The old stuff is simply not accounting for true anecdotes like that. The feedpoint had to be retuned, of course. 4) I don't know how I would find out the exact methodology of how they laid the radials in the RCA Labs case. Were they cut shorter and shorter? Did they PICK UP the radials in lowering the count, or just disconnect them at the center. K7LXC et al in their multiband vertical comparison found differences based on the ground drying out. Did the '37 study drench the field to start? How did they deal with that? How did they deal with the changing impedance at the feed point as radials were varied? A) constant current in the radiator for a set height as radial count changed, with constant power in the radiator to set the current for various heights? Or B) just constant power to the feed? The former is a classic researcher's technique, done that way to isolate the effect of the radials from other current changing issues. The latter is what happens to hams. And it means that you can't use the Labs Case 3.6 dB difference to say that 2 radials is only 3.6 dB down from 120 radials if what you're talking about is how much amplifier to add in lieu of adding radials to your radial field to work Europe from the US. You have to know what the effective series R of the radial system is, what the feed R for the vertical is, figure the loss for the two in series and at least ADD 3.6 dB to that loss. And if there is some ground modality enhancement skewing the 3.6 dB you would have to add that difference as well. Just one more reason the RBN tells a truth seemingly untouched by the old studies. Note that if you're dense and uniform, none of this nastiness applies. Shameless plugs for real radial systems will continue. 5) And at this point, buried in anecdotal material, I am willing to surmise that the single helicopter measurement suite I have heard about in conjunction with some radial tests was made to confirm that the skywave was as predicted over the DENSE, LONG, gold standard version they were proving in. Not done over the crap setup. We are interested in how the crap setup works, because that is what is so often getting done out there. We need to know how crap setup actually works so we can devise alternatives to do maximum improvements where dense and uniform is not possible. I've been the meter guy in a helicopter making commercial field strength measurements at heights (and with a GPS to nail the measurement points). You don't have to go very far back in time for helicopter measurements, without the aid of GPS, to have necessary "approximate" aspects to the data. The helicopter guy had JUST INSTALLED the GPS, and it was his favorite new toy. Further, when you go up flying for something like that, it is PLANNED. Points, altitudes, climbing times, descending times, and horizontal travel times and make measurements hovering and gradually descending are laid out in a book that is being read as the process goes on. The pilot's time is spent entirely operating the aircraft, avoiding other traffic and moving to points read by the meter guy. JUST A SINGLE SET of data run on only one set of conditions on the ground uses up the fuel and flight time and chases the copter back to the airport for fuel. You would be making an airport cycle for each set of data if you were running multiples. And, personally, you would not get me to do two of those in a day. FAR too busy and nerve-wracking. You make those count. No extra cycles thrown in to make some hams happy on an issue not related to THE money issue paying for the helicopter ride. The money issue that had me up there was phase cancellation distortion in a quadrant of the FM coverage area. We had to know if the field from the antenna was smoothly varying or not with changes in height and bearing, and how it played out over the coverage area. MFR said antenna would side mount on the big tower, but apparently did not account for interaction with the tower cross members. The field strength in the air at various distances and bearings proved it out. Get UP, measure THAT, and get DOWN. Period. Bossy station manager has a budget. Helicopter pilot cut off some of my tests anyway, fuel got down to the go home level. Station Manager peeved about time to actually get tests. Fussy about the cost, but the results made our case. Readings were used to make a case with the MFR and things went forward from there and got rectified. Did NOT go back up to see if things changed. Bossy station manager has a budget. Again back to the point that RBN (carefully used) is the first real sky wave measuring gizmo not filled with tons of assumptions, that us plain folk have easy access to. The data needed to really deal with and confront issues for sky wave and the un-dense and un-uniform is being gathered now. Really for the first time in history. We just need to get past invalid assumptions about what happens when one extrapolates a proven dense and uniform downward into the murky waters of minimal and miscellaneous "radial" counterpoises. 73, Guy. On Sun, Nov 6, 2011 at 5:41 AM, Richard Fry <[email protected]> wrote: > Guy Olinger wrote: >>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. > > That isn't exactly correct, Guy. > > The 1937 real-world experiments of Brown, Lewis & Epstein of RCA Labs > includes measured data for sets of of radials varying in number from 2 to > 113, and in length from 0.137 to 0.412 lambda. The paper at > http://i62.photobucket.com/albums/h85/rfry-100/BLandERadials.gif shows the > results for the longer two sets. > >>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. > > The results of the BL&E experiments show that for monopole heights ranging > from about 45º to > 90º using 113 or more symmetrical, buried radials each > at least 0.412 lambda physical length in free space, the groundwave field > measured 3/10 mile from the monopole will be within several percent of its > theoretical maximum value for the same applied power to a perfect monopole > driven against a perfect ground plane. > > In essence this means that the real conductivity of the earth in which that > number/length of radials is buried has a very little affect on the radiation > "launched" by that monopole antenna system. > > These tests were done at 3 MHz at a site in NJ where earth conductivity was > not better than 4 mS/m, so they certainly are applicable for 160-m monopole > systems used by hams. > > A good means to test the performance of a monopole antenna system is to > measure the groundwave field it produces within 1/2 mile or so, and compare > it to the theroretical value it would have if that power was radiated by > that system with zero loss in its connection to r-f ground (as per BL&E). > Doing this accurately takes an expensive, calibrated F.I. meter which few > hams have, but maybe they could borrow/rent one for a few hours from a local > AM broadcast station. The results of the test would show whether they could > benefit from adding more/longer wires to a given set of less than 120 x > 1/4-wave buried radials. > > Rather than be overly concerned about the conductivity of the earth within > 1/2-lambda of a monopole, one could install a "broadcast" type system of 120 > x 1/4-wave buried radials, and be done with it. Such systems using monopoles > having physical heights of 45º to > 90º will radiate about 95% of the > applied power, regardless of soil conductivity within the area of the > radials. > > Once radiation is launched from a vertical monopole* it is subject to > whatever real earth conductivity exists beyond the radius of the buried > radial system. That will affect both the groundwave and the skywave. > > But there isn't much that be done about this, except to move the monopole > system to a geographical region having better conductivity. > > * The shape of the elevation pattern from a given monopole is the same no > matter what the application. All unloaded monopole heights up to 5/8 lambda > radiate (launch) maximum field in the horizontal plane. Hams may be more > interested in skywave propagation paths than some Class C AM broadcast > stations, but that does not mean that a monopole has zero field in the > horizontal plane and at small elevation angles above it, as sometimes is > concluded by looking at "far-field" plots produced by NEC software, and > found in antenna textbooks. > > RF > > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
