Transmitters, Modulation and Processing
RF power amplifiers
The output tuning controls on a transmitter power amplifier:
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allow switching to different antennas
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Correct Answerallow efficient transfer of power to the antenna
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reduce the possibility of crossmodulation in adjunct receivers
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are involved with frequency multiplication in the previous stage
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The purpose of using a centre-tap return connection on the secondary of transmitting tube's filament transformer is to:
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Correct Answerprevent modulation of the emitted wave by the alternating current filament supply
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reduce the possibility of harmonic emissions
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keep the output voltage constant with a varying load
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obtain optimum power output
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In a grounded grid amplifier using a triode vacuum tube, the input signal is applied to:
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Correct Answerthe cathode
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the plate
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the control grid
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the filaments
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In a grounded grid amplifier using a triode vacuum tube, the plate is connected to the pi-network through a:
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by-pass capacitor
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tuning capacitor
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electrolytic capacitor
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Correct Answerblocking capacitor
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In a grounded grid amplifier using a triode vacuum tube, the plate is connected to a radio frequency choke. The other end of the radio frequency choke connects to the:
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filament voltage
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Correct AnswerB+ (high voltage)
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ground
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B- (bias)
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In a grounded grid amplifier using a triode vacuum tube, the cathode is connected to a radio frequency choke. The other end of the radio frequency choke connects to the:
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ground
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filament voltage
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Correct AnswerB- (bias)
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B+ (high voltage)
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In a grounded grid amplifier using a triode vacuum tube, the secondary winding of a transformer is connected directly to the vacuum tube. This transformer provides:
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B- (bias)
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B+ (high voltage)
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Screen voltage
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Correct Answerfilament voltage
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In a grounded grid amplifier using a triode vacuum tube, what would be the approximate B+ voltage required for an output of 400 watts at 400 mA with approximately 50 percent efficiency?
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500 volts
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Correct Answer2000 volts
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3000 volts
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1000 volts
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In a grounded grid amplifier using a triode vacuum tube, each side of the filament is connected to a capacitor whose other end is connected to ground. These are:
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tuning capacitors
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Correct Answerby-pass capacitors
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electrolytic capacitors
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blocking capacitors
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After you have opened a VHF power amplifier to make internal tuning adjustments, what should you do before you turn the amplifier on?
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Make sure that the power interlock switch is bypassed so you can test the amplifier
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Correct AnswerBe certain all amplifier shielding is fastened in place
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Be certain no antenna is attached so that you will not cause any interference
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Remove all amplifier shielding to ensure maximum cooling
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Harmonics produced in an early stage of a transmitter may be reduced in a later stage by :
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larger value coupling capacitors
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greater input to the final stage
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Correct Answertuned circuit coupling between stages
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transistors instead of tubes
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