The following link talks about wind turbine towers but is equally applicable to radio towers. Lots of reading and links included.
Lightning Protection
Lightning Protection
Poked around on here today. This is an amazing library of info!Solar City is in the Wayback Machine.
https://web.archive.org/web/20120206114347/http://www.solacity.com/Lightning.htm
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Disconnecting the shack is the only true lightning protection!! No grounding in the world will save your equipment if you take a direct hit!! All of this helps with RFI, static discharge, and turns the odds in your favor during a thunderstorm. Please don't ever think you are lightning proof though, unless you have disconnected the shack.