Hi. Richard I've been following this thread -mostly for entertainment.
I've noted your postings re elevated radials to replace deteriorated buried radial fields under broadcast towers. I'm familiar with the work and the results. This work, of course was done by professional broadcast engineers with significant instrumentation at their disposal. Of course, they also had to measure the field intensity in the far field and file it with the FCC. Their work seemed to show that, once we have installed 4 elevated 1/4 wave radials we're reaching the point of "diminishing returns" and that little is to be gained by increasing the number of radials beyond 4. I'm sure you appreciate by now that there are a LOT of authoritative and fervently held opinions that are spouted in this reflector without any supporting data or results. And we "can't reason people out of positions that they didn't arrive at through reason"!! Most hams do not seem to appreciate that a 160m inverted -L with elevated 1/4 wave resonant radials is, in fact, a ground-plane antenna, with the vertical radiator bent to make use of available supports and should be considered and analyzed as such! Nevertheless, there are a LOT of authoritative pronouncements like "as many as possible" (elevated radials) or "as high as possible" (again for elevated radials - and this only serves to reduce the effective height of the high-current portion of the vertical radiator). Hams seem more inclined to rely on apocrypha, and "hearsay" from folks that they consider to be authoritative topband "gurus". These views, though passionately and fervently held, generally are lacking of supporting data, and theoretical support. They are entertaining, but not really helpful! There seems to be something "mysterious" and "sacred" in the topband community about "dirt"! About the only rationale that I can arrive at for buried radials is if one is shunt feeding a grounded tower. If the vertical radiator can be isolated from ground, then the elevated resonant radials will do very nicely. I ran 160m inverted Ls with resonant elevated radials for years - usually 3 or 4, but sometimes just two, and a couple of them had to be "bent" because of lot limitations. With 500-600W I could be heard pretty much anywhere in the world - VK6,3B8,ZL,ZS, KH6,.JA and "deep" Russians etc. from my lot in NC. My problem was never being heard- it was HEARING!(I helped the hearing issue a LOT when I put in some "Kaz" terminated loops that could be accommodated on my city lot.) My radials were not very high 5-6 feet along the property fence lies and one ran along under the eaves of my one-story house because it was convenient. It all worked really well until Hurricane Fran took down the tree that was supporting the far end of the inverted L that was about 75 feet. Because of intervening hip replacement surgery and a long recovery I haven't rebuilt it -yet. But have hopes and plans for this summer. Anyway, reasoning, or arguing, with topband hams about antennas is a lot like having a religious or political discourse. Generally they seem to just BELIEVE! I do appreciate and value your posts on this reflector. Best regards, Charlie, K4OTV Charles Cunningham Jr, PE P.S. Elevated radial DO need to be high enough that we (or wildlife) don't r un inti them -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Richard Fry Sent: Tuesday, March 05, 2013 6:45 PM To: [email protected] Subject: Re: Topband: Elevated Radials Guy Olinger posted: >...The very same NEC 4.2 with raised quarter wave radials over routine real >life ground made of dirt will show field intensities in the ground. (etc >etc) _______________ Sorry, but this is a misunderstanding/misuse of NEC for this situation. The r-f currents flowing in the earth under and near elevated, horizontal radials are NOT the source for the r-f currents flowing on those radials, themselves. Those radial wire currents are supplied by the currents flowing on the inside surface of the outer conductor of a coaxial transmission line used to drive the monopole -- which is connected to the common point of those elevated radial wires. Elevated radials behave much differently than buried radials. In effect, driving a vertical monopole against an even number of geometrically- symmetric pairs of at least two elevated, horizontal wires used as a counterpoise converts a base fed (unbalanced) monopole radiator into a balanced radiator -- which neither needs, nor can use a structural connection to the earth for most efficient system performance. For proof of this, please study the measurements of a real-world system using 4 x 1/4-wave elevated radials described in the link below, for/at WPCI, 1490 kHz in Greenville, SC, and the rest of that paper. http://www.commtechrf.com/documents/nab1995.pdf RF _________________ Topband Reflector _________________ Topband Reflector
