coherent transponder การใช้

After the new uplink station achieved a 2-way coherent transponder lock in which the spacecraft generated its carrier at 240 / 221 times the received uplink frequency, the new ground station ranged the spacecraft . Then the ranging signal was turned off and the range measurement was continually updated by Doppler velocity measurements.
Allocating uplink / downlink frequency pairs in a fixed ratio of 221 / 240 permitted the use of coherent transponders on the spacecraft . The spacecraft tracked the uplink carrier with a phase locked loop and, with a series of frequency dividers and multipliers, multiplied the uplink carrier frequency by the ratio 240 / 221 to produce its own downlink carrier signal.