Arecibo

Here's the page I got that figure from:

http://www.oldradio.com/current/bc_am.htm

Scroll down a bit:

"Dave Hersherger adds: "Apparently, the highest ERP is produced by the
interplanetary radar transmitter at Arecibo, Puerto Rico. Continental
built this transmitter too - it's a 1 megawatt (CW, not pulsed) S band
(2300 MHz) source. It's two klystrons, at 500 kilowatts apiece,
combined for a megawatt CW.

"The dish at Arecibo (seen in the movie "Contact") has a gain of 74 dB
(!) at S-band. And with the interplanetary radar running, the ERP is
23.6 - not megawatts - not gigawatts - but TERAWATTS (i.e. 23.6E+12
watts or 23,600,000,000,000 watts). I have been told that this is
equivalent to the energy flux of a small star.

"When the Arecibo transmitter was being built, it was called the "E.T.
Phone Home" transmitter. When that thing was fired up it glitched the
power line so bad that every PC that wasn't on a UPS rebooted, and the
phones all started ringing.""

> The other part of it which didn't quite sound right to me was the talk of
> terawatts. Correct me if I'm wrong, but isn't terawatts a unit of measure
> more appropriate to discussions of global energy usage?

ERP refers to "Effective Radiated Power"

http://encyclopedia.laborlawtalk.com/Effective_radiated_power

"...if the antenna is directional, the ERP figure is usually the
maximum in any one direction, rather than the average."