Photo of oscilloscope display showing the first reflection of a radar signal from the Moon, achieved on January 10, 1946 by the US Signal Corps Project Diana. The radar, in Fort Monmouth, New Jersey, USA, was a modified US Army WW2 SCR-271 set producing 1/4 second pulses at a power of 50 kW at 111.5 MHz, driving a "billboard" reflective array antenna consisting of 64 dipoles in front of a screen reflector giving 24 dB gain. The righthand pulse is the transmitted signal, while the smaller lefthand pulse is the return signal. It took the signal 2.4 seconds to make the 477,000 mile round trip journey from the Earth to the Moon and back. The horizontal axis of the oscilloscope trace is time, but it is calibrated in miles; it can be seen that the round trip time is equivalent to a range of 238,000 miles, the distance from the Earth to the Moon.