The little yellow radio shown in the movie was a actual radio. Its design is based on a WWII German emergency transmitter. It is a BC-778/SCR-578/AN-CRT3 emergency transmitter (it could not receive) affectionately called 'Gibson Girl', a name taken from the narrow-waisted female drawings of 1890s fashion artist Charles Gibson. Its shape allowed the operator to hold it between the legs while cranking it the necessary 80 RPM to produce enough electricity to operate. It could be set to automatically send an SOS signal or switched to send Morse Code signals. Early models transmitted only on 500kHz, later models also could transmit on 8280kHz (later modified to 8364kHz). It was notorious for being tough to crank.
The general plot is based on a true story that the author, Ernest Gann related in his 1961 autobiographical book about his flying career, "Fate is the Hunter". He and other pilots searched successfully for a lost fellow pilot in the wilds of northern Canada during World War II.