E7H Oscillators and signal sources: types of oscillators; synthesizers and phase-locked loops; direct digital synthesizers; stabilizing thermal drift; microphonics; high-accuracy oscillators
- E7H01 (D)
What are three common oscillator circuits?
- A. Taft, Pierce, and negative feedback
- B. Pierce, Fenner, and Beane
- C. Taft, Hartley, and Pierce
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| D. Colpitts, Hartley, and Pierce |
- E7H02 (C)
What is a microphonic?
- A. An IC used for amplifying microphone signals
- B. Distortion caused by RF pickup on the microphone cable
- C. Changes in oscillator frequency caused by mechanical vibration
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| D. Excess loading of the microphone by an oscillator |
- E7H03 (C)
What is a phase-locked loop?
- A. An electronic servo loop consisting of a ratio detector, reactance modulator, and voltage-controlled oscillator
- B. An electronic circuit also known as a monostable multivibrator
- C. An electronic servo loop consisting of a phase detector, a low-pass filter, a voltage-controlled oscillator, and a stable reference oscillator
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| D. An electronic circuit consisting of a precision push-pull amplifier with a differential phase input |
- E7H04 (C)
How is positive feedback supplied in a Colpitts oscillator?
- A. Through a tapped coil
- B. Through link coupling
- C. Through a capacitive divider
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| D. Through a neutralizing capacitor |
- E7H05 (D)
How is positive feedback supplied in a Pierce oscillator?
- A. Through a tapped coil
- B. Through link coupling
- C. Through a neutralizing capacitor
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| D. Through a quartz crystal |
- E7H06 (B)
Which of these functions can be performed by a phase-locked loop?
- A. Wide-band AF and RF power amplification
- B. Frequency synthesis and FM demodulation
- C. Photovoltaic conversion and optical coupling
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| D. Comparison of two digital input signals and digital pulse counting |
- E7H07 (D)
How can an oscillator’s microphonic responses be reduced?
- A. Use NP0 capacitors
- B. Reduce noise on the oscillator’s power supply
- C. Increase the gain
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| D. Mechanically isolate the oscillator circuitry from its enclosure |
- E7H08 (A)
Which of the following components can be used to reduce thermal drift in crystal oscillators?
- A. NP0 capacitors
- B. Toroidal inductors
- C. Wirewound resistors
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| D. Non-inductive resistors |
- E7H09 (A)
What type of frequency synthesizer circuit uses a phase accumulator, lookup table, digital-to-analog converter, and a low-pass anti-alias filter?
- A. A direct digital synthesizer
- B. A hybrid synthesizer
- C. A phase-locked loop synthesizer
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| D. A direct conversion synthesizer |
- E7H10 (B)
What information is contained in the lookup table of a direct digital synthesizer (DDS)?
- A. The phase relationship between a reference oscillator and the output waveform
- B. Amplitude values that represent the desired waveform
- C. The phase relationship between a voltage-controlled oscillator and the output waveform
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| D. Frequently used receiver and transmitter frequencies |
- E7H11 (C)
What are the major spectral impurity components of direct digital synthesizers?
- A. Broadband noise
- B. Digital conversion noise
- C. Spurious signals at discrete frequencies
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| D. Harmonics of the local oscillator |
- E7H12 (B)
Which of the following ensures that a crystal oscillator operates on the frequency specified by the crystal manufacturer?
- A. Provide the crystal with a specified parallel inductance
- B. Provide the crystal with a specified parallel capacitance
- C. Bias the crystal at a specified voltage
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| D. Bias the crystal at a specified current |
- E7H13 (D)
Which of the following is a technique for providing highly accurate and stable oscillators needed for microwave transmission and reception?
- A. Use a GPS signal reference
- B. Use a rubidium stabilized reference oscillator
- C. Use a temperature-controlled high Q dielectric resonator
- D. All these choices are correct
