In MISTRAM, this was avoided by broadcasting a continuous signal. The basic system used a ground station located down range from the launch site (at Valkaria, Florida and Eleuthera Island, Bahamas) and a transponder on the vehicle. The tracking station transmitted an X-band carrier signal which the transponder responded to by re-broadcasting it on another (shifted) frequency. By slowly changing the frequency of the carrier broadcast from the station and comparing this with the phase of the signal being returned, ground control could measure the distance to the vehicle very accurately. Even with the analog circuitry used, MISTRAM was accurate to less than 1 km at the distance of the moon.