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Re: Topband: Optimum number of radials for given wire length

 To: topband@contesting.com Re: Topband: Optimum number of radials for given wire length Garry Shapiro garry@ni6t.com Sat, 14 Aug 2010 21:29:25 -0700 mailto:topband@contesting.com>
 ``` On 8/13/2010 9:29 AM, Richard (Eagle-Eye) Karlquist wrote: >> I have the ARRL's ANTENNA BOOK 20th Edition, and on Chapter 3 (The >> Effects of the Earth), p.3-10 is Table 1 tht maybe contains all you want >> about that. >> If you haven't the book here is the table: >> >> Number of radials 16 24 36 60 90 120 >> >> Length of each radial in 0.10 0.125 0.15 0.20 0.25 0.40 >> wavelengths >> >> Spacing of radials in degrees 22.5 15 10 6 4 3 >> >> Total length of radial wire 1.6 3 5.4 12 22.5 48 >> installed in wavelengths >> >> Power loss in dB at low angles 3 2 1.5 1 0.5 0* >> >> with a L/4 radiating element >> >> Feed-point impedance in ohms 52 46 43 40 37 35 >> with a L/4 radiating element >> >> * compared to a perfectly conducting ground >> >> 73 Panos SV1GRD >> > The dB loss numbers vs feed point impedance don't make sense to me. > To get 3 dB loss, the feed point impedance should be 70 ohms, not > 52 ohms. The dB numbers seem to be off by a factor of 2, IMHO, > like they used 20 LOG instead of 10 LOG. > > Also, if your antenna is less than 1/4 wavelength, then of course > the dB loss entries will be considerably different, etc. > > Rick N6RK And he is right, iff "power loss in dB at low angles" correlates 1:1 with ground losses. In that case the 16 ohms of equivalent loss dissipate 31% of the power, or -1.6 dB, not -3dB. But perhaps "power loss in dB at low angles" was calculated by integrating the radiation pattern and reflects both ohmic ground loss and the change in pseudo-Brewster angle. How low is "low" is not specified. Garry, NI6T _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK ```
 Current Thread Topband: Optimum number of radials for given wire length, Frank Topband: Optimum number of radials for given wire length, Πανος Δαλάκος Re: Topband: Optimum number of radials for given wire length, Richard (Rick) Karlquist Re: Topband: Optimum number of radials for given wire length, Garry Shapiro <=