Scrolling through various shortwave frequencies, caught couple tones among the noise. Sounded like sad horns. Radio used was a grundig yacht boy 207 with a broken antenna, recorded on a tascam dr-05x.
This tone was generated using audacity. In the base there is a 45hz sinusoid. Then a new sinusoid tone of 207hz is added for about 5s. After a pause of about 5s a second sinusoid of 208hz is added for 5s.
A sound stimuli to demonstrate combination tone from speakers. You should hear additional frequency of 500 hz. The sound itself is summation of1000 hz and 1500 hz.