Complex sentence: This is "not" the amount of power that a broadcast station reports as its ERP, such as "we're 100,000 watts of rock' n' roll", but is in fact many times less for the high-power VHF and UHF stations.
Split into simpler sentences: This is "not" the amount of power that a broadcast station reports as its power, as in "we're 100,000 watts of rock' n' roll", which is usually the effective radiated power (ERP). The transmitter power output is normally less than the ERP; in fact, it is many times less for the high-power VHF and UHF stations.