7 1-57.   Which, if any, of the following advantages is a primary benefit of plate modulation? 1.  It operates at low efficiency 2.  It operates at low power levels 3.  It operates with high efficiency 4.  None of the above 1-58.   A final rf power amplifier biased for plate modulation operates in what class of operation? 1.  A 2.  B 3.  AB 4.  C 1-59.   Heterodyning action in a plate modulator takes place in what circuit? 1.  Grid 2.  Plate 3.  Screen 4.  Cathode 1-60.   A plate modulator produces a modulated rf output by controlling which of the following voltages? 1.  Plate voltage 2.  Cathode voltage 3.  Grid-bias voltage 4.  Grid-input voltage 1-61.   To achieve 100-percent modulation in a plate modulator, what maximum voltage must the modulator tube be capable of providing to the final power amplifier (fpa)? 1.  Twice the fpa plate voltage 2.  The same as the fpa plate voltage 3.  Three times the fpa plate voltage 4.  Half the fpa plate voltage 1-62.   In a plate modulator, with no modulation, how will the plate current of the final rf amplifier appear on a scope? 1.  A series of pulses at the carrier frequency 2.  A series of pulses at twice the carrier frequency 3.  A series of pulses at 1/4 the carrier frequency 4.  A series of pulses at 1/2 the carrier frequency 1-63.   In the collector-injection modulator, af and rf are heterodyned by injecting the rf into (a) what circuit and the af into (b) what circuit? 1.  (a) Base (b) collector 2.  (a) Base (b) emitter 3.  (a) Emitter (b) collector 4.  (a) Emitter (b) base 1-64.   Plate- and collector-injection modulators are the most commonly used modulators for which of the following reasons? 1.  The rf amplifier stages can be operated class C for linearity 2.  The rf amplifier stages can be operated class C for maximum efficiency 3.  They require small amounts of audio power 4.  They require large amounts of audio power 1-65.   A control-grid modulator would be used in which of the following situations? 1.  In extremely high-power, wideband equipment where high-level modulation is difficult to achieve 2.  In cases where the use of a minimum of audio power is desired 3.  In portable and mobile equipment to reduce size and power requirements 4.  Each of the above