Unified S-band

The Unified S-band (USB) system was a tracking and communication system developed for the Apollo program by NASA and the Jet Propulsion Laboratory (JPL). It operated in the S band portion of the microwave spectrum, unifying voice communications, television, telemetry, command, tracking and ranging into a single system to save size and weight and simplify operations. The USB ground network was managed by the Goddard Space Flight Center (GSFC). Commercial contractors included Collins Radio, Blaw-Knox, Motorola and Energy Systems.

The previous programs, Mercury and Gemini, had separate radio systems for voice, telemetry, and tracking. Uplink voice and command, and downlink voice and telemetry data were sent via ultra high frequency (UHF) and very high frequency (VHF) systems. The tracking capability was a C band beacon interrogated by a ground-based radar. With the much greater distance of Apollo, passive ranging was not feasible, so a new active ranging system was required. Apollo also planned to use television transmissions, which were not supported by the existing systems. Finally, the use of three different frequencies complicated the spacecraft systems and ground support. The Unified S-band (USB) system was developed to address these concerns.

The USB system did not completely replace all other radio transmitters on Apollo. While it was the sole mode for deep space communications, Apollo still used VHF for short range voice and low rate telemetry between astronauts and the Lunar Module (LM) and lunar rover during extra-vehicular activity; between the LM and Command/Service Module (CSM or CM); and between the CSM and Earth stations during the orbital and recovery phases of the mission. The CM had a backup capability to range the LM over its VHF voice links.

...
Wikipedia