Morse code, SOS signal reception:
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High-frequency squeak, Low-frequency rumble
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Electronic signal, energy buildup
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Morse code transmission
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High frequency pulsating electronic signal
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SOS signal reception, Morse code
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Geiger counter
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Brown noise
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Low frequency pulsing and humming signal
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Morse code, SOS signal transmission
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Electronic signal
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Low frequency electronic signal
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White noise
★★★★★