Sources

Books

American Radio Relay League,  The A.R.R.L. Antenna Book, Newington Connecticut: American Radio Relay League Inc., 1964

King, Gordon J.,  The Practical Aerial Handbook, London: Newnes-Butterworths, 1970

Pictures barrowed from the fallowing web sites

http://www.cometantenna.com/

http://www.lbl.gov/MicroWorlds/Contents/Contents.html

http://www.naic.edu/vpublic/vcenter/aovef.htm