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Modulation in Radio-Frequency

Quiz Questions

1.____________ is the ability to impress intelligence upon a transmission medium, such as radio waves.
2. The rate at which the vector rotates determines the FREQUENCY of the sine wave that is generated; that is, the faster the vector rotates, the more cycles completed in a given time period.
3.The process of combining two or more frequencies in non-linear impedance results in the production of new frequencies. This process is referred to as______________.
4.Two conditions must be met in a circuit for heterodyning to occur. First, at least two different frequencies must be applied to the circuit. Second, these signals must be applied to non-linear impedance.
5.Amplitude modulation refers to any method of varying the amplitude of an electromagnetic carrier frequency in accordance with the intelligence to be transmitted by the carrier.
6.The “on-off” KEYING of a ______________carrier frequency was the principal method of modulating a carrier in the early days of electrical communications.
Continuous wave
7.When greater frequency stability is required, the oscillator should be keyed, but should remain in continuous operation; other transmitter circuits may be keyed
8.The categories of cw transmitters are as follows:
Master oscillator power amplifier (mopa) transmitters,
Multistage, high-power transmitters,
High- and very-high frequency transmitters
All of the above
9.The main advantage of a mopa transmitter is that the power-amplifier stage isolates the oscillator from the antenna. This prevents changes in antenna-to-ground capacitance from affecting the oscillator frequency.
10.A______________ is an energy converter that changes sound energy into electrical energy.
11.The sensitivity or efficiency of a microphone is usually expressed in terms of the electrical power level, which the microphone delivers to a matched-impedance load compared to the sound level being converted.
12.An AM transmitter can be divided into major sections according to the frequencies at which they operate:
Radio frequency (rf) unit
Audio frequency (af) unit
a & b
None of the above
13.What does FCC stand for?
Federal Communications Commission
Federal Communication Council
Federal Communications and Connections
None of the above
14.To measure degrees of modulation less than 100 percent, you can use a MODULATION FACTOR (M) to indicate the relative magnitudes of the rf carrier and the audio-modulating signal. Numerically, the modulation factor is:
(Refer Pg 1-48)
Modulation in Radio-Frequency 1
What does Em stand for in the above equation?
RMS value of the modulation voltage
None of the above
15.Plate modulation permits the transmitter to operate with high efficiency. It is the simplest of the modulators available and is also the easiest to adjust for proper operation.
16._______________ is modulation produced in the plate circuit of the last radio stage of the system.
High-Level Modulation
Low-Level Modulation
17.The modulation index as a formula is shown below:
Modulation in Radio-Frequency 2
What does ∆f stand for?
Frequency deviation
Modulation frequency
Modulation factor
None of the above
18.In frequency modulation (fm) the instantaneous frequency of the radio frequency wave is varied in accordance with the modulating signal; the amplitude of the radio-frequency wave is kept constant.
19._____________________ is modulation in which we allow oscillations to occur for a given period of time only during selected intervals.
Pulse modulation
Phase Shift Keying
20.Pulse Code Modulation is a method of pulse modulation in which the modulating wave is used to frequency modulate a pulse-generating circuit.