On Feb 23, 7:57 pm, Scott wrote:
OK, I take that answer...now, why did the FCC go with an ERP as that
would require calculation rather than a measurement. Hard to measure
ERP as far as I know...


Because ERP (or EIRP, depending on the application) is how most
licensing works, because that's what's important for spectrum
management in a shared band. Ham radio is somewhat unique in that the
rules are applied on power somewhere in the middle of the system (i.e.
in the feedline from Tx to antenna), with no limits (except for RF
safety) on the radiated field strength. If you can build a 60dBi
antenna and radiate 1.5 GW EIRP, you can do it. (part of that
'encouraging experimentation and advances in the radio art').

yes, commercial broadcast is regulated in terms of power output, but,
since you have to do a "proof of performance" and demonstrate that you
have a certain field strength at a distance, it's really regulating
ERP. Change your antenna gain, and they can conceivably make you
change your Tx power.