[recording by Ary Boender]
This very strange station is one of several multi-frequency tone modes (ENIGMA XPx) that come from Russian Intelligence. They are "numbers" broadcasts, but the digits are mapped to audio tones. Other tones are used for formatting purposes. This particular Polytone, the high pitched variant, uses 14 tones spaced 16 Hz apart. A slow callup is broadcast, then the message speeds up to a tone rate of 7-8 per second.
The above plot is logarithmic, taken just as the fast portion begins. The same tone is sent 10 times. Sync? I don't know. Also note how clipped the signal is, especially on the positive side, making it extremely rich in harmonics. This is not the recording, as the basic waveform stays the same in ionospheric fades.
The wideband, linear plot below further dramatizes these striking characteristics. We see the extremely clicky, phase-noisy keying, and harmonics out to the 15th. Awesome.
Documents filed after several recent high-profile espionage arrests in the USA and Germany describe the automatic computer decoding of Russian broadcasts that are probably the Polytones. This stuff most likely really IS for spies.
All plots made with GRAM.EXE.