Yes Guy, I agree. Another area that is overlooked perhaps through a lack of room is the need with short verticals to have longer radials to get back the system efficiency. Take my own as an example I only use a 51ft vertical which is top loaded. That of course will tell you the antenna is fairly Low Z, in order to get the efficiency back to as high as possible I laid 130 x 0.4 wave radials. With this I know that the effective series ground resistance in my case is about a couple of ohms, and the overall result is good. So the unfortunate reality for amateurs is the shorter the vertical is from a quarter wave, Ideally the longer the radials need to be. 73 Clive GM3POI
-----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Guy Olinger K2AV Sent: 24 February 2015 16:07 To: Richard Fry Cc: TopBand List Subject: Re: Topband: Modeling "Ground" On Tue, Feb 24, 2015 at 7:36 AM, Richard Fry <[email protected]> wrote: > NEC4 produces accurate answers for monopole radiators _not_ using > "overkill" radial systems, as long as the NEC model describes the real > world conditions for that system. You wish. You're not considering the situation that everyone is complaining about. NEC x.x does not provide accurate answers for "UNDERkill" radial systems either. I've never heard of a skilled ham getting trounced on 160 who has a 1/4 wave radiator over an overkill radial system. While it might be argued that the ham really didn't have to put down that much copper, at worst he only wasted money. He's still doing right fine getting out on his highly efficient, if over-coppered antenna, and enjoying it. On the other hand, UNDERkill radial systems, too short, not enough, irregular lengths, non-uniform around the compass, especially over poorer ground, are what NEC x.x also significantly overestimates. Advice had by many, including myself, has really been off. I still am waiting for an apology for some glib advice given, resulting in a couple S units worth of unnecessary loss. I was told some number of times regarding my complaining of really poor results that I must be doing something wrong, as the advice had been "verified by professionals and the FCC". I'm still hearing that selfsame blanket unqualified advice. Wrong then. Wrong now. Conversions from underkill radials to something efficient designed for limited space opportunities have generated conversion improvements anywhere from five to twelve dB, based on before and after strings of RBN reports. 7-8 dB is very common in these conversion exercises, raising suspicions of some singular issue not treated correctly or at all in NEC. Underkill radials are proven amplifier neutralizers. NEC does NOT directly calculate ground losses after the fashion of its highly accurate wire and tubing calculations. Sommerfeld and all the rest are tuned APPROXIMATION algorithms that seem well-calibrated only in the commercial BC paradigm. The NEC ground APPROXIMATION tuning misses by wide margins in small lots that are not lucky enough to be in 30 mS superdirt. You can say all you want, but there is now (past tense, already happened) a massive experience among hams who are using new methods to get a decent signal on 160, and they just won't believe the old line any more. They have their own experience in their backyard, and RBN reports, and new signal reports from longtime ham acquaintances well situated to report general changes in signal strength. And they simply don't care if NEC is accurate for commercial grade radial systems. It's a completely useless piece of information for them. Most hams do not have the land and circumstances to put down anything remotely resembling a commercially sized radial system. You're really only talking to property-rich hams, and leaving the vast majority to learn the hard way that what you are preaching does not apply to them. 73, Guy. _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
