Real data: I am presently using a 30' base loaded vertical. The ground system consists of 90 radials from 12 to 25 feet. The base referred ground loss is 10 ohms.
Dave WX7G On Sep 27, 2012 6:26 PM, "W2XJ" <[email protected]> wrote: > Richard > > The data is indisputable but I think for the average ham about a dozen 45 > degree radials will produce about 3 DB less than theoretical. That is less > than an S unit. The other difference is that all this information is based > on ground wave propagation. There is nothing that addresses higher angle > sky wave propagation common for 160 M operation. > > Sent from my iPad > > On Sep 27, 2012, at 7:38 PM, "Richard Fry" <[email protected]> wrote: > > > Guy Olinger wrote: > > > >> Can you pass along your source of information that BL&E was done over 4 > mS/m soil, ... Or are you using the FCC map for typical soil conductivities > and presuming a common New Jersey value and no variation at the site? > > > > It is my presumption that for their cost and logistics, and with my 15 > years of insight as an RCA Broadcast field engineer (1965-1980), the BL&E > measurements were made near Princeton, NJ. I'll try to confirm that, and > advise. Princeton was the corporate facility containing the > office/laboratory of George H. Brown. > > > > If those tests had been made at some physical location where earth > conductivity at/near the test site was significantly better than in New > Jersey, this would have been evident in their measured data. > > > > For an example of this, if earth conductivity at/near the test site was > 30 mS/m, then even relatively few/relatively short buried radials in > contact with that earth would enable higher radiated fields than shown in > the BL&E data for those radial numbers and lengths. This is illustrated by > the NEC4 study using a short monopole on 1.85 MHz at this link: > http://i62.photobucket.com/albums/h85/rfry-100/10m_Vert32Buried_Radials.jpg. > > > > Even for an earth conductivity of 4 mS/m, the BL&E data show that > monopoles ranging from about 45 to at least 90 degrees in physical height, > driven against an r-f ground system consisting of at least 113 x 0.412-wave > buried radials, produces a groundwave field at 3/10 of a mile that is > within several percent of the maximum theoretical value possible for a > perfect monopole driven against a perfect ground plane, for that applied > power. > > > > The bottom line in all of this is that the worse the earth conductivity > within 1/2-wavelength of the base of a monopole (especially a short > monopole) while driving that monopole against a set of buried radials, the > more important it becomes to use a large number of such radials of lengths > approaching 1/2 of a free space wavelength. > > _______________________________________________ > > UR RST IS ... ... ..9 QSB QSB - hw? BK > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
