Chayka (Russian: Чайка, lit. "seagull") also known as Radioteknicheskaya Systema Dalyoloiy Navigatsii abbreviated as RSDN (lit. Russian Hyperbolic Radio Navigation System) is a Russian terrestrial radio navigation system, similar to Loran-C. It operates on similar frequencies around 100 kHz, and uses the same techniques of comparing both the envelope and the signal phase to accurately determine location. The systems differ primarily in details.