MIL 188-110 39 

A PSK system implemented per MIL-STD-188-110A, 39-tone modem appendix B. The system supports data rates of 75 to 2400bps using 39 tones spread from 675Hz to 2812.5Hz with a spacing of 56.25Hz. 1 doppler tone can be found at 393.75Hz. Block interleaving with up to 12s delay is supported. A 39-tone modem sounds like noise, so as you tune across this signal an S meter will rise and fall. It soundsvery much like tuning a noisy frequency.

IF-bandwidth of the receiver must be at least 3 KHz wide to enable undistorted decoding. 

A MIL188-110 39tone signal together with an ALE signal and Oscilloscope and FFT running. 
(FFT showing the typical ALE signal)