Is that MP3 actual raw recordings, or has it been "enhanced" with interesting interference. I'm hearing lots of echo, telemetry, different voiced "layered" on top of each other, etc.
The "echo" is actually from multiple spatially separated stations simultaneously transmitting the same message. You're hearing the differences in time of flight. The overlapping signals don't interfere as one might expect because they use single sideband modulation.
There is a lot of interesting interference at these low frequencies. I didn't hear anything I wouldn't expect to hear on HF. Also, echo is a complex and somewhat mysterious topic. Long Path echo is easily grasped; the same signal is received twice due to two paths around the Earth which happens when band conditions are favorable. Other forms of echo (Long delayed echo[1], for example) are less easily explained.
