The radiation resistance is not easy to calculate, because it
depends critically on how well coupled the oscillator is to the radiation
fields, i.e. on how good an antenna the circuit is. This will depend, in
turn on, the frequency of the oscillation. If some part of the circuit
has a dimension of order c/f, it will radiate reasonably well. Otherwise,
most of the energy will indeed end up as heat.
Us old amateur radio types know that all too well!
Dr. Mark H. Shapiro
Physics Department
California State University, Fullerton
P.O. Box 6866
Fullerton, California 92834-6866