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45 Cards in this Set
- Front
- Back
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What are the two types of electrical communications?
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Radio and wire.
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What is the main advantage of radiotelegraph communications?
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Reliability.
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Why is radiotelephone one of the most useful methods of military communications?
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It is direct, convenient and easy to use.
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What are the disadvantages of radiotelephone communications?
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Static, enemy interference or a high local noise level.
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What is the main use of a radio teletypewriter?
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High speed automatic communications across ocean areas.
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What is facsimile?
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The process used to transmit photographs, charts and other graphic information electronically.
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A system is subdivided into what levels?
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Set, group, unit, assembly, subassembly, and part.
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In the example 1A6CR3, what is the assembly designator?
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A6.
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he majority of vlf transmitters are used for what purpose?
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Fleet communications or navigation.
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Today the Navy uses lf communications as a segment of what operational system?
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Fleet Multichannel Broadcast System.
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Why does the Navy only use the upper and lower ends of the mf band?
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Due to the commercial broadcast (AM) band.
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What are the four general types of communications services in the hf band?
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Point-to-point, ship-to-shore, ground-to-air, and fleet broadcast.
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A message transmitted on several frequencies at the same time is an example of what type of
transmission? |
Frequency-diversity.
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Physically separating receive antennas is an example of what technique?
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Space-diversity.
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When using frequencies above 30 megahertz, you are normally limited to using what range?
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Line of sight.
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The naval communications system is made up of what two groups of communications?
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Strategic and tactical.
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What are the five most prominent communications modes of operation?
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Simplex, half-duplex, semiduplex, duplex, and broadcast.
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What four switched networks are part of the defense communications system?
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AUTOVON, AUTOSEVOCOM, AUTODIN, and DSSCS.
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What two elements support only designated Navy requirements?
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HICOM and NORATS.
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What are the four basic transmitter types?
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Am, fm, cw, ssb.
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What is the function of the oscillator in a cw transmitter?
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It generates an rf carrier at a given frequency within required limits.
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What is the final stage of a transmitter?
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Power amplifier.
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What purpose does a microphone perform in an AM transmitter?
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It converts audio (sound) into electrical energy.
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In an fm transmitter, when does an oscillator generate only a steady frequency?
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When no modulation is present.
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What is a harmonic?
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It is an exact multiple of the basic or fundamental frequency.
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If the fundamental frequency is 200 megahertz, what is the third harmonic?
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600 megahertz.
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Why are frequency multipliers used?
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To obtain higher carrier frequencies.
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What are two advantages of ssb transmission?
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It saves power and frequency bandwidth.
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What is the purpose of an order-wire circuit?
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For operator-to-operator service messages and frequency changes.
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What four basic functions must a receiver perform?
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Reception, selection, detection, and reproduction.
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What are the four basic receiver characteristics?
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Sensitivity, noise, selectivity, and fidelity.
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What frequency conversion principle is used to develop the IF?
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Heterodyning.
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What is the function of the detector?
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To extract the modulating audio signal.
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What is the major disadvantage of an fm signal as compared to an AM signal?
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Wide bandpass.
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What two components give a ssb receiver its advantages over an AM superheterodyne receiver?
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A special type of detector and a carrier reinsertion oscillator.
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What does manual gain control do to strong and weak signals, respectively?
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A special type of detector and a carrier reinsertion oscillator.
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What is the purpose of agc/avc in a receiver?
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To limit unwanted variations in the output.
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What is a disadvantage of agc?
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Weak signals produce bias, which could result in no usable receiver output.
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What is the main difference between agc and dagc?
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Dagc does not attenuate weak signals.
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What is the function of the bfo?
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It is heterodyned with the rf to produce an audio frequency.
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What is the purpose of a squelch circuit?
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It is heterodyned with the rf to produce an audio frequency.
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What does a tone control circuit in a receiver do to the audio signal?
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It controls the amount of bass and treble response.
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What is the function of a crystal filter in a receiver?
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It is used to achieve maximum selectivity.
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What is the primary function of an afc circuit?
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It is used to accurately control the frequency of the oscillator.
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What is frequency synthesis?
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The process of selecting and/or heterodyning frequencies to produce a signal frequency.
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