| 21. | The diode tube was a reliable alternative for detecting radio signals.
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| 22. | Remember, your tracer must be able to send radio signals out.
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| 23. | No high buildings or mountains obscure the radio signals transmitted over the Internet.
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| 24. | Andes is far from urban services and the mountainous terrain blocks radio signals.
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| 25. | These stations have radio signals that travel only a few miles.
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| 26. | The radio signal will consisted on short beeps and long pauses.
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| 27. | Before heterodyning, radio signals often overrode and interfered with each other.
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| 28. | Researchers know that heat and moisture in the atmosphere can distort radio signals.
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| 29. | Within this gas cloud is water vapor, which tends to amplify radio signals.
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| 30. | Ten minutes later the Egyptians intercepted a radio signal in Hebrew.
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