ISS Elements: Ultra High Frequency (UHF) antenna
Source: Shuttle Press Kit
The Ultra High Frequency (UHF) antenna is attached to the U.S. laboratory Destiny. The antenna, on a four-foot boom, is part of the UHF Communications Subsystem of the station. It will interact with systems already aboard the ISS, including the Space-to-Space Station Radio (SSSR) transceivers. A second antenna will be delivered on STS-115/11A.
The UHF subsystem is used for space-to-space communication (voice, commands and telemetry for the space station). It can support up to five users on the same frequency and provides:
Two-way voice communications between the station and space walkers, the station and orbiter and between the Mission Control Center in Houston and space walkers (using the UHF with the S-band subsystem).
Orbiter commanding of critical station functions such as going to free drift during undocking operations. Commands are encrypted for security.
ISS transmission of critical telemetry to the orbiter during undocking operations.