In a similar vein, John Kraus (Of Antennas... textbook fame) described a gravitational transmitting and receiving system as a fun (?) diversion near the end of the book.

It has been a few years, but I seem to recall that the transmitter was a 500T steel bar spun at very close to the maximum RPM the tensile strength of steel allowed; the radiated energy was something like a fraction of an attowatt. (An attowatt = 1*10^-18W)

There are more efficient transmitting schemes out there.