Further to recent discussions on ground systems, there is some very good
information in the "Vertical Antenna Handbook" by Capt. Paul Lee K6TS, in
the CQ Technical Series. Figure 15 shows the following field strengths from
a quarter wave antenna at 1 mile, for 1 kW ERP (N = number of radials):
Radial Length N=113 N=15
0.375 lambda 193 mV/m 156 mV/m
0.250 lambda 186 mV/m 154 mV/m
0.125 lambda 155 mV/m 148 mV/m
The theoretical maximum field strength at 1 mile is 196 mV/m, so the ground
loss with 113 radials 3/8 wave long will be only 0.13 dB.
K6TS emphasizes that these are the "unattenuated field strengths", i.e.
perfect propagation in the half plane above ground to the 1 mile point. The
data is based on extensive measurements by G. H. Brown, published in his
paper "Ground Systems As A Factor In Antenna Efficiency", Proc. IRE June 1957.
Regarding ground systems for phased arrays, K6TS says "where radials
overlap, they should be joined... the whole ground system should be one well
bonded unit with no loose connections or unsoldered crossing wires."
73,
Peter VK3APN
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Sponsored by Akorn Access, Inc & N4VJ / K4AAA
|