2016-E7E: Modulation and demodulation: reactance, phase and balanced modulators; detectors; mixer stages
Which of the following can be used to generate FM phone emissions?
A reactance modulator on the oscillator
A balanced modulator on the audio amplifier
A reactance modulator on the final amplifier
A balanced modulator on the oscillator
What is the function of a reactance modulator?
To produce PM signals by using an electrically variable inductance or capacitance
To produce PM signals by using an electrically variable resistance
To produce AM signals by using an electrically variable inductance or capacitance
To produce AM signals by using an electrically variable resistance
How does an analog phase modulator function?
By varying the tuning of an amplifier tank circuit to produce PM signals
By varying the tuning of a microphone preamplifier to produce PM signals
By varying the tuning of an amplifier tank circuit to produce AM signals
By varying the tuning of a microphone preamplifier to produce AM signals
What is one way a single-sideband phone signal can be generated?
By using a balanced modulator followed by a filter
By using a reactance modulator followed by a mixer
By using a loop modulator followed by a mixer
By driving a product detector with a DSB signal
What circuit is added to an FM transmitter to boost the higher audio frequencies?
A pre-emphasis network
A de-emphasis network
A heterodyne suppressor
An audio prescaler
Why is de-emphasis commonly used in FM communications receivers?
For compatibility with transmitters using phase modulation
To reduce impulse noise reception
For higher efficiency
To remove third-order distortion products
What is meant by the term baseband in radio communications?
The frequency components present in the modulating signal
The lowest frequency band that the transmitter or receiver covers
The unmodulated bandwidth of the transmitted signal
The basic oscillator frequency in an FM transmitter that is multiplied to increase the deviation and carrier frequency
What are the principal frequencies that appear at the output of a mixer circuit?
The two input frequencies along with their sum and difference frequencies
Two and four times the original frequency
The sum, difference and square root of the input frequencies
1.414 and 0.707 times the input frequency
What occurs when an excessive amount of signal energy reaches a mixer circuit?
Spurious mixer products are generated
Mixer blanking occurs
Automatic limiting occurs
A beat frequency is generated
How does a diode detector function?
By rectification and filtering of RF signals
By breakdown of the Zener voltage
By mixing signals with noise in the transition region of the diode
By sensing the change of reactance in the diode with respect to frequency
Which type of detector is used for demodulating SSB signals?
What is a frequency discriminator stage in a FM receiver?
A circuit for detecting FM signals
An FM generator circuit
A circuit for filtering two closely adjacent signals
An automatic band-switching circuit
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