Dave wrote:

 From what I know about EME, amateurs use reasonably high powers, of the order of 100's of Watts, with many using several thousand (not officially so, but in practice they do).

While I won't say amateur EME operators never exceed FCC limits, I don't see it being a common practice.

You may see *effective radiated powers* quoted which well exceed the 1500 watt amateur power limit.  These figures take the directional characteristics of the antenna into account - its action in concentrating the available power along the horizon and in the direction of the receiving station.  (or reflector -- moon -- in the case of EME work)  Unlike the broadcast services, in the amateur service only the transmitter output power is regulated.  As long as you limit your transmitter output to 1500 watts, you can use as much effective radiated power as your antenna can develop.  (consistent with safety)

Which is probably more than you wanted to know<grin>.

> This implies a power 6-7 orders of magnitude higher than what amateurs > use, which puts it into the GW power levels. It is not obvious how
> those sorts of powers will be readily achieved.

VERY big antennas<grin>