Morse code, SOS signal transmission:
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High frequency signal
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Radio noise
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Reception, Morse code, transfer
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Low frequency electronic signal
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Morse code, SOS signal transmission
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Radar, location alert
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High frequency pulsating electronic signal
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High-frequency squeak, Low-frequency rumble
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Morse code, welcome
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Radio Setup
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Interference Broadcasting
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SOS signal reception, Morse code
★★★★★