Hight of "A" by lighting info
http://www.gordtelecom.com/FAAAStd.htm This web site divide Antennas into a 3 categories for lighting requirments.
A series, D series, and E series.
Note that the site states: that the "below is a brief respresentation, for accurate information please follow the links provided at bottom of this page."
Also, many have already seen the below circular...
http://www.airweb.faa.gov/...ILE/AC70_7460_1K.pdf