18 2-56.   What is the maximum amount of phase shift provided by the C3-R_B network? 1.  90 degrees 2.  80 degrees 3.  70 degrees 4.  60 degrees 2-57.   Which of the following is the correct formula for the resonant frequency of a phase-shift oscillator? 1. 3. 2. 4. 2-58.   Which of the following oscillators is used to provide a highly stable output at a very precise frequency? 1.  Crystal 2.  Hartley 3.  Colpitts 4.  Armstrong 2-59.   The frequency of a crystal-controlled oscillator is determined by which of the following physical actions? 1.  Type of cut 2.  Accuracy of cut 3.  Thickness of grinding 4.  All of the above 2-60.   Why is the crystal in a crystal-controlled oscillator often installed in a temperature- controlled oven? 1.  To increase frequency without changing the crystal 2.  To decrease frequency without changing the crystal 3.  To provide better amplitude stability 4.  To provide better frequency stability Figure 2E.—Frequency response of a crystal. IN ANSWERING QUESTIONS 2-61 THROUGH 2-64, REFER TO FIGURE 2E.  THE LETTERS A, B, C, D, AND E ARE POINTS ON THE FREQUENCY-RESPONSE CURVE FROM WHICH YOU SHOULD SELECT ANSWERS TO THE QUESTIONS. 2-61.   At what point on the curve does a crystal act as a series-tuned circuit? 1.  A 2.  B 3.  C 4.  D 2-62.   At what point does the crystal act inductively? 1.  A 2.  B 3.  C 4.  D 2-63.   Below series resonance, a crystal acts capacitively at what point on the curve? 1.  A 2.  B 3.  C 4.  E 2-64.   At what point does the crystal act purely as a parallel-resonant circuit? 1.  B 2.  C 3.  D 4.  E