[BC] Ground system

[Richard Fry]

RE  Elevated Radials

Below is a clip from a paper on this topic by Clarence Beverage, published 
in the 1995 NAB Engineering Handbook.

 \ \ INSTALLED ELEVATED SYSTEMS
In November of 1988, our firm supervised the construction of a temporary 
antenna system in Newburgh, New York under FCC Special Field Test Authority 
using call sign KPI-204. The antenna system consisted of a lightweight, 15 
inch face tower, 120 feet in height, with a base insulator at the 15 foot 
elevation and six elevated radials, a quarter wave in length, spaced evenly 
around the tower and elevated 15 feet above the ground. The radials were 
fully insulated from ground and supported at the ends by wooden tripods. 
Approximately ten feet above ground, a T network for matching the antenna 
was mounted on a piece of marine plywood to isolate the components from 
contact with the lower section of the tower which was grounded. Power was 
fed to the system through a 200 foot length of coaxial cable with the cable 
shield connected to the shunt element of the T network and to the elevated 
radials. A balun or RF choke on the feedline was not employed and the 
feedline was isolated from the lower section of the tower. The system 
operated on 1580 kHz at a power of 750 watts.

The efficiency of the antenna was determined by radial field intensity 
measurements along 12 radials extending out to a distance of up to 85 
kilometers. The measured RMS efficiency was 287 mV/m for 1 kW, at one 
kilometer, which is the same measured value as would be expected for a 0.17 
wave tower above 120 buried radials. / /

(From: New AM Broadcast Antenna Designs Having Field Validated Performance)

The complete paper can be downloaded from the CTI website at the link below.
Free registration is required.

http://www.commtechrf.com/amantenna.asp