ABSTRACT
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The communications subsystem is responsible for reception and demodulation of
signals sent up from the ground station (uplink) as well as transmission of signals
back to the ground station (downlink). The system is also responsible for any commu-
nication with other satellites. The uplink signal consists of commands and range
tones, which are signals first transmitted by the ground station, and then received
and retransmitted by the satellite. The delay is used to determine the satellite’s distance
from the station. In addition to range tones, the downlink signal includes telemetry for
spacecraft status and any payload data. The downlink signal is usually coherent in
phase with the uplink signal, which allows for Doppler shift detection of spacecraft
velocity.
