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## Re: Topband: Elevated Radial Efficiency - an inordinately long post

 To: "William Culpepper" , Re: Topband: Elevated Radial Efficiency - an inordinately long post "Tom Rauch" Tom Rauch Thu, 29 Nov 2007 12:15:15 -0500
 ```Hi Bill, I strongly disagree that the early tests and articles meant very much. First, they deluded Hams into thinking 120 radials are needed to achieve maximum efficiency in an array. The truth is the efficiency curve of eff vs. number of radials flattens out in most cases with as few as 40-50 radials. Second, it wasn't a good test for measuring a variation of a few dB. >I am ONE of the people who claim that four elevated radials >can have > approximately the same efficiency as 120 buried quarter > wavelength radials. The only possible way to make that test with any reasonable accuracy would be to install four elevated radials over virgin soil and then remove them and replace them with 60 or 120 radials on the ground while measuring FS at the very same points. I'll explain why below. > I have installed such systems at three Standard Broadcast > stations in the > United States, and made field strength measurements that, > when analyzed in > accordance with FCC procedure, showed that the > unattenuated field strength > at one kilometer was essentially the same as the FCC > criteria for broadcast > antennas with 120 buried 90 degree radials (Figure 8 of > Part 73 of the FCC > Rules). The FCC test works like this: 1.) A person measures the slope of the FS changealong straight lines radiating out from the antenna for a considerable distance. 2.) From that slope a person finds a "best match" to a graph. This graph then estimates the average conductivity along that path. 3.) From that estimated conductivity a person then estimates the expected FS and expresses it normalized to some standard, like a kilowatt at a kilometer. The problem is the variables and the human element. There are many wobbles and variations in the slope of FS curves. Sometimes even moving just a few feet, a person can make an array have any efficiency he wants within reason! It's easy to have 10dB of variation with radial distance with just a few feet of movement!! So what does the person use? As an example if we look at the FS measurements Belrose used in an elevated radial article, the slope of the FS could be matched to two or three different curves. Not only that, he picked the "best" radial direction for estimating a high efficiency. The "wobble" or deviation in slope was 2-3dB or more over very small distances in points along a radial direction. It just happened that picking the worse sloped curve made the earth look lossy, and that made the array look better because it makes the EXPECTED FS look much lower. This means the array efficiency looked better. If the mean value of slope was used the earth loss would have looked better, and the array efficiency looked worse. Even by picking another direction the array would have looked worse. The FCC estimate is also an average of the entire path, not the localized conductivity. It treats the earth as a homogeneous media with constant conductivity. That isn't the real earth. Making the tests even less reliable, one of the early elevated radials tests was made over soil that contained unknown remaining radials from a earlier ground. Who can say how much effect that added to the mix?? So how would we do a good test with minimal chance for error???? We could do a good test by changing nothing except the radials, and measuring at exactly the same points. Then we don't need to match dozens and dozens of readings into a sloped curve, and then transform that result into another estimate of what we should have at a certain distance, and then find a spot at that distance that proves we get what we guessed we should get. We simply go back to the very same point and record the change with only one thing changed, the radials. The result is the exact deviation caused by the ground system, within limits of human error and instrument calibration. The result is not a long process of matching curves to estimate the soil conductivity, and then extrapolating that conductivity data into an estimate of efficiency based on the estimated soil conditions along the path and expected FS at a certain distance. We actually did several tests where FS was measured with a small elevated system and with no changes at all other than the radials FS was remeasured. In those tests four elevated radials that were ground isolated were compared to a conventional ground of 60 radials with no change except the radials themselves. The results showed the small elevated system was a few dB to 6 dB down from 60 radials. This test repeated with similar results at three locations, one of which was WVNJ radio. WVNJ was a good test because they never had a conventional ground, they started with four elevated radials. It was easy to watch the FS at measurement points increase 2-5dB as the ground system was changed by adding more and more radials. Roy Lewallen was out here last year, and we found four elevated radials about the same as 10-15 radials in the dirt. That was on 40 meters. Why would I put up with all the headaches of suspending an antenna and radials up several feet and NOT having good lightning protection when I could just tack 10-15 radials down on the ground and have a normal system that works exactly the same? 73 Tom _______________________________________________ Topband mailing list Topband@contesting.com http://lists.contesting.com/mailman/listinfo/topband ```
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