[BC] Directional Antenna Proofs - Ground systems.

[Richard Fry]

>The elevated radials need to be at least 0.1 Lamda above the ground.

The quote below was clipped from Clarence Beverage's paper at 
http://lkk.do.am/_ld/0/53_nab1995.pdf .  The height of the elevated radials 
in this installation was only 0.024 lambda (~8.8 degrees), yet the measured 
efficiency of the system was 302 mV/m (at 1 km for 1 kW of applied power).

NEC models show similar performance even with lower elevated radial heights 
in wavelengths, but such heights probably have been avoided for better 
personnel safety, and to allow uncluttered access to the land area under the 
radials.

 \\ The first permanent use of an elevated radial ground system appears to 
be at WPCI, 1490 kHz in Greenville, South Carolina. This installation, 
designed by William A. Culpepper, involved replacing a standard buried 
system with a four wire elevated system consisting of #10 solid copper wire, 
one quarter wave in length, and supported on treated wooden posts which keep 
the radials 4.9 meters above ground. The antenna radiation efficiency, based 
on field strength readings on the eight cardinal radials, was 302 mV/m at 1 
kilometer versus the predicted FCC value of 307 mV/m. The WPCI installation 
was unique in that the tower was base insulated but the radials came right 
up to the tower, 4.9 meters above ground and terminated in insulators. The 
tower was fed from the tuning unit, through a piece of coax to the 5 meter 
point on the tower where the center conductor of the coax was attached to 
the tower and the shield to the elevated radials. This feed system resulted 
in a higher feed resistance than would normally be expected. Data on this 
facility was taken from the FCC files. //

RF