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I know that electromagnetic waves like radio travel freely without a medium, even through the vacuum of space. But, I also know that physical structures like buildings, walls, bodies can filter and block EM waves from reaching a destination.

Could it be possible that if a loud enough pressure wave was created (e.g. gunshot), it could interrupt a radio signal? Possibly that the air molecules compress to a high density just for a moment, long enough to create a quick filter or interruption/delay in a radio transmission?

Context: I record sound for a living and needed to record gunshots for SFX libraries one day. I use RF transmitters to send wireless audio to my receiver/sound recorder.

I had my radio receiver and audio recorder beside the marksman, while the wireless transmitter was sending me audio from faaar downrange. The idea was to capture the impact of bullets as well as a soft reverb tail.

I noticed that every time a shot was fired, I could hear the gunshot sound in my recorder immediately as per normal, but then a repeating/oscillating RF hit would cycle maybe 10 times while fading to inaudible. I'm familiar with what RF hits sound like from my job, but I've never heard them mimic an audio transmission in a repetitive cycle like this.

This day I was in an isolated location in the Arctic and my RF scans showed absolutely no offending RF interference in the operating range. I was not clipping the mic as these transmitters were not close enough to the gun.

I was thinking maybe some kind of sharp ripple in air density that could make it harder for a radio wave to swim against? Forgive my lack of physics knowledge!

I'm truly puzzled but any insight would be very educational for me. Thanks in advance!

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  • $\begingroup$ Help: what is SPL? $\endgroup$ – garyp Feb 21 at 11:57
  • $\begingroup$ Some more details would help. How far apart were the two microphones/transmitters, and where was the receiver relative to them? What was the repetition rate of the repeating/oscillating signal? Do you have a detailed temporal profile of the repeating/oscillating signal? $\endgroup$ – S. McGrew Feb 21 at 12:28
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Searching for an effect by google I came up with this theoretical paper:

The abstact contains nuggets that could explain your observation

The reflection of electromagnetic waves normally incident on the wavefronts of a semi‐infinite standing sound wave in a liquid is discussed theoretically. Since the reflecting planes of maximum sound pressure disappear periodically, the reflected electromagnetic signal is modulated with the acoustic frequency. The modulated reflected electromagnetic wave arises (1) from the microscopic movement of the liquid surface, and (2) from the direct analog of Bragg reflection in optics. The second effect is most pronounced when the wavelength of the electromagnetic radiation in the liquid is twice the acoustic wavelength.

Maybe if you do not get an answer by an expert, you could get in touch with the authors.

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