Transmission From the International Space Station: ISS Repeater in Action #hamradio

Audio transmitted directly from the International Space Station (ISS) demonstrates the operation of its amateur radio crossband repeater. This system is situated aboard the ISS, which orbits Earth at an altitude around 400 kilometers. The service functions by receiving signals transmitted from ground-based amateur radio operators, processing them onboard, and retransmitting them back toward Earth, effectively enabling long-distance communication via the spacecraft relay.

The downlink frequency for this ISS repeater transmission is specified as 437.8 MHz. Due to the high relative velocity between the ISS and ground observers, reception often requires compensation for a Doppler shift reaching up to ±10 kHz. Successful reception by radio enthusiasts relies on appropriate equipment, precise frequency tuning, and accurate awareness of the ISS orbital passes, which each offer a brief window for communication.