[TowerTalk] A fundamental antenna question

[Wesley Cosand]

Folks:

I am embarrassed to ask a question I should be able to figure out but my 
Handbook and Antenna Book aren't proving sufficient to overcome my ignorance.

How can I calculate the field strength in volts/meter as a function of 
distance from an isotropic antenna emitting a given power in watts?  (Let's 
ignore the near field/far field issue.)  Where does a ham go for this kind 
of information?

Thanks

Wes, WZ7I