Earth-Moon L1

Smaller transmitter and receiver sizes are practical with higher
microwave transmission frequencies, although that requires higher
quality antennas also. The typical frequency Charles is probably
assuming is 2.5 GHz, but there's nothing particularly special about that
number, other than FCC regulations and atmospheric considerations,
neither of which apply to the Moon. At 250 GHz, the two would need to be
only 1/10 the diameter (see
http://www.spacefuture.com/archive/a_few_things_you_occasionally_wanted_to_know_about_wireless_power_transmission.shtml
for example).

Also, the transmitting antenna does not need to be a single continuous
object of several hundred meters or kilometers across - rather several
transmitting antennas can work together in "phased array mode" to
produce a single main beam lobe at the receiving location.

In other words, I believe the demo could be quite a bit smaller than
Charles suggests.

Arthur