Topband: Elevated Radials
rfry at adams.net
Tue Mar 5 05:56:46 EST 2013
Developing this topic a little more, the link below shows a NEC4.2 model of
a 1/4-wave, vertical monopole driven against a set of 4 x 1/4-wave
horizontal wires used as an elevated counterpoise. The base of the monopole
and the elevation of the radial wires are set to 4.9 meters, as in the
Culpepper system I posted earlier in this thread (Sat, 2 March 2013 at
04.33:34 -0600). The relative amplitudes and phases are shown for each
conductor. Frequency is 1490 kHz. The system was modeled over perfect
This system produces an inverse distance groundwave field of ~313 mV/m at
1 km for 1 kW of applied power. This is the maximum theoretical field
possible for those conditions for a perfect, series-fed, 1/4-wave monopole
base-driven against a perfect ground plane.
The azimuth radiation pattern is perfectly circular. This is as expected,
because the only conductor producing useful far-field radiation is the
vertical monopole, itself. There is no physical reason why that radiation
should be other than omnidirectional, at all elevation angles.
But while the performance shown by this NEC model is identical to that of a
perfect monopole with its base attached to a perfect, flat ground plane of
infinite extent, none of the r-f current flowing on the vertical section has
needed to flow through the earth to reach the monopole. In fact, the NEC
model HAS no structural connection to the earth !
No earth currents will flow along the vertical monopole in such elevated
systems even when they are installed just above a non-perfect ground plane,
such as the earth.
This illustrates how such an elevated system using only 4 x 1/4-wave
horizontal wires as a counterpoise can equal the performance of a
conventional 1/4-wave monopole using as many as 120 x 1/2-wave radials
buried in real earth.
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