E7E Modulation and demodulation: reactance, phase, and balanced modulators; detectors; mixers
- E7E01 (B)
Which of the following can be used to generate FM phone signals? #card
- A. Balanced modulation of the audio amplifier
- B. Reactance modulation of a local oscillator
- C. Reactance modulation of the final amplifier
- D. Balanced modulation of a local oscillator
- E7E02 (D)
What is the function of a reactance modulator? #card
- A. Produce PM or FM signals by varying a resistance
- B. Produce AM signals by varying an inductance
- C. Produce AM signals by varying a resistance
- D. Produce PM or FM signals by varying a capacitance
- E7E03 (D)
What is a frequency discriminator? #card
- A. An FM generator circuit
- B. A circuit for filtering closely adjacent signals
- C. An automatic band-switching circuit
- D. A circuit for detecting FM signals
- E7E04 (A)
What is one way to produce a single-sideband phone signal? #card
- A. Use a balanced modulator followed by a filter
- B. Use a reactance modulator followed by a mixer
- C. Use a loop modulator followed by a mixer
- D. Use a product detector with a DSB signal
- E7E05 (D)
What is added to an FM speech channel to boost the higher audio frequencies? #card
- A. A de-emphasis network
- B. A harmonic enhancer
- C. A heterodyne enhancer
- D. A pre-emphasis network
- E7E06 (A)
Why is de-emphasis used in FM communications receivers? #card
- A. For compatibility with transmitters using phase modulation
- B. To reduce impulse noise reception
- C. For higher efficiency
- D. To remove third-order distortion products
- E7E07 (B)
What is meant by the term “baseband” in radio communications? #card
- A. The lowest frequency band that the transmitter or receiver covers
- B. The frequency range occupied by a message signal prior to modulation
- C. The unmodulated bandwidth of the transmitted signal
- D. The basic oscillator frequency in an FM transmitter that is multiplied to increase the deviation and carrier frequency
- E7E08 (C)
What are the principal frequencies that appear at the output of a mixer? #card
- A. Two and four times the input frequency
- B. The square root of the product of input frequencies
- C. The two input frequencies along with their sum and difference frequencies
- D. 1.414 and 0.707 times the input frequency
- E7E09 (A)
What occurs when the input signal levels to a mixer are too high? #card
- A. Spurious mixer products are generated
- B. Mixer blanking occurs
- C. Automatic limiting occurs
- D. Excessive AGC voltage levels are generated
- E7E10 (A)
How does a diode envelope detector function? #card
- A. By rectification and filtering of RF signals
- B. By breakdown of the Zener voltage
- C. By mixing signals with noise in the transition region of the diode
- D. By sensing the change of reactance in the diode with respect to frequency
- E7E11 (C)
Which type of detector is used for demodulating SSB signals? #card
- A. Discriminator
- B. Phase detector
- C. Product detector
- D. Phase comparator
