So, if there were a tunnel straight through the earth from the US to either Australia or South Africa (~7800 miles long), at the speed of light, information would take at least 40 milliseconds to reach the other side.

Assuming we constructed a Tesla tower technology and placed an automated repeater station at the antipode with a translator, such that any time it received a byte of data, it would translate it according to a defined function and re-transmit it.

If the translated echo were received back at the originating station in less than 80 ms, that is a very easy to measure length of time.

In fact, even a distance as small as ten miles using a similar setup would be very easy to verify, as the round-trip time would be about 100 microseconds, also readily measured with off-the-shelf timing equipment.

So where do I find a design for the transmitter and receiver of such impulses? It would also be quite simple to factor out the time required to process the signals at either end of this circuit...