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  2. Hertz Systems - Wikipedia

    en.wikipedia.org/wiki/Hertz_Systems

    Hertz Systems Ltd is a Polish company based in Zielona Gora that utilizes space technology for both the military and civilian markets, primarily relying on GPS navigation. Hertz Systems cooperates with, among others, the European Space Agency , [ 1 ] the Polish Space Agency , the Space Research Center of Polish Academy of Sciences and NATO ...

  3. The Thing (listening device) - Wikipedia

    en.wikipedia.org/wiki/The_Thing_(listening_device)

    A receiver demodulated the signal so that sound picked up by the microphone could be heard, just as an ordinary radio receiver demodulates radio signals and outputs sound. Its design made the listening device very difficult to detect, because it was very small, had no power supply or active electronic components, and did not radiate any signal ...

  4. Survival radio - Wikipedia

    en.wikipedia.org/wiki/Survival_radio

    AN/URC-11 - Operating at 243 megahertz (1.23 m), "A" versions replaced one audio tube with transistors. [8] AN/URC-10 - Subminiaturized, completely transistorized UHF radio sets consisting of a crystal-controlled receiver-transmitter, a 16-volt dry battery, and a power cable assembly. The unit operates on one channel in the 240–260 megahertz ...

  5. Marine VHF radio - Wikipedia

    en.wikipedia.org/wiki/Marine_VHF_radio

    Marine VHF radio is a worldwide system of two way radio transceivers on ships and watercraft used for bidirectional voice communication from ship-to-ship, ship-to-shore (for example with harbormasters), and in certain circumstances ship-to-aircraft.

  6. Long-range acoustic device - Wikipedia

    en.wikipedia.org/wiki/Long-range_acoustic_device

    A long-range acoustic device (LRAD), acoustic hailing device (AHD) or sound cannon is a specialized loudspeaker that produces sound at high power for communicating at a distance. It has been used as a method of crowd control , which has caused permanent hearing damage , having an extremely high decibel capacity (up to 160 dB measured at one ...

  7. Spark-gap transmitter - Wikipedia

    en.wikipedia.org/wiki/Spark-gap_transmitter

    The receiver in most systems also used two inductively coupled circuits, with the antenna an "open" resonant circuit coupled through an oscillation transformer to a "closed" resonant circuit containing the detector. A radio system with a "two circuit" (inductively coupled) transmitter and receiver was called a "four circuit" system.