  The use of modern software-defined radio (SDR) devices enables the
implementation of efficient communication systems in numerous scenarios. Such
technology comes especially handy in the context of search and rescue (SAR)
systems, enabling the incorporation of additional communication data
transmission into the otherwise sub-optimally used SAR bands at 121.5 and
243~MHz. In this work, we propose a novel low-complexity, energy-efficient
modulation scheme that allows transmission of additional data within chirped
homing signals, while still meeting the standards of international SAR systems
such as COSPAS-SARSAT. The proposed method modulates information onto small
deviations of the chirp slope with respect to the required unmodulated chirp,
which can be easily detected at the receiver side using digital signal
processing.
