Citation :
121.750 MHz FM Narrow mode Space Shuttle/Mir air-to- air Low transmit power used during rendezvous/docking and undocking/separation.
259.700 MHz AM mode Space Shuttle voice uplink/downlink Used from prelaunch to launch +1 hr. 40 min., during in-orbit radio checks with Edwards AFB and Kennedy Space Center on the day before landing, used for radio checks with the landing site on the final fly-over before de-orbit, and from landing - 2 hr. 25 min. to touchdown.
The Space Shuttle transmits on three frequency bands: UHF, S-Band, and Ku-Band. The UHF frequencies are simple AM voice and are very easy to copy. These frequencies are used for launch and landing operations, EVA operations, and as an additional voice downlink when other channels are in use for the current ground station has no S-Band capability. The frequencies in use are:
296.800 Mhz: Air-to-ground, or Orbiter to suit 259.700 Mhz: Air-to-ground, or suit to Orbiter 279.000 Mhz: Suit-to-Orbiter, or suit-to-suit
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