Your Name: @ 3.145.19.0

1. Another name for demodulation is:

a) Selection
b) Acquisition
c) Detection
d) None of these

2. The DC bias for the RF and IF stages in a superheterodyne receiver is derived partly from:

a) The audio power amplifier
b) The 2nd IF amplifier
c) The local oscillator
d) The AM detector
e) None of these

3. A mixer has two frequencies being applied, 700 KHz and 1000 KHz. Which of these gives the ideal output frequencies?

a) 700 KHz, 1000 KHz
b) 700 KHz, 1000 KHz, 1700 KHz
c) 700 KHz, 1000 KHz, 1700 KHz, 300 KHz
d) None of these

4. Which section of a superhet receiver determines the receiver's bandwidth?

a) Detector
b) Preselector
c) IF Amplifier
d) None of these

5. A mixer is producing the following frequency outputs: 710 KHz, 455 KHz, 1165 KHz, 1875 KHz. What are the two most likely frequencies being applied?

a) 710 KHz, 1165 KHz
b) 1875 KHz, 1165 KHz
c) 1000 KHz, 875 KHz
d) 262.5 KHz, 300 KHz
e) None of these

6. How is a mixer forced to be nonlinear?

a) One frequency applied is higher than the other
b) It is driven into large-signal mode by one of the signal sources
c) The power supply to the mixer is made as large as possible
d) None of these

7. A superhet receiver is using high-side injection. The incoming RF signal has a carrier frequency of 560 KHz; the IF frequency is 455 KHz. What is the image frequency?

a) 1470 KHz
b) 1015 KHz
c) 1120 KHz
d) 1165 KHz
e) None of these

8. What is the advantage of having a constant-frequency amplifier (the IF amplifier) in a superheterodyne receiver?

a) The gain can be held constant
b) The noise is minimized
c) The bandwidth will be constant
d) None of these

9. In a superhet receiver, the difference between the preselector and local oscillator frequencies should always be:

a) The IF frequency
b) The carrier frequency
c) One-half the local oscillator frequency
d) None of these

10. Which portion of a PLL is primarily responsible for determining the capture range?

a) VCO
b) Phase Detector
c) Low-Pass Filter
d) Reference Divider

11. Given that N=2442, R=10240, and F1 = 10.240 MHz, what will the output frequency Fout of the PLL synthesizer above be?

a) 1.024 MHz
b) 20.480 MHz
c) 8.192 MHz
d) 2.442 MHz

12. When the REFERENCE and VCO frequencies are equal, what state is a PLL in?

a) Free-Running
b) Capture
c) Lock
d) None of the above

13. In the PLL pictured above, the following measurements were made:

F1 = 10.000 MHz
"A" = 0 KHz (Steady +100 mV DC signal)
"B" = 55 KHz (5 Vpp square wave)
VCO Control Voltage = 0.3 V (Steady DC); Vcc = 8.0 V
"D" = 55.055 MHz (Unstable; this is an average).

It is known that R = 100 and N = 1001 from the service documentation. What is the most likely fault in the loop?

a) The N divider is defective (Not triggering correctly on VCO signal)
b) The R divider is defective (Not producing correct frequency at TP "A")
c) The VCO is defective (Not oscillating)
d) The phase detector is defective (Not comparing "A" and "B")
e) The loop is operating correctly

14. What two signals should be compared by a technician to determine whether or not a PLL is in lock?

a) The VCO output and the REFERENCE
b) The VCO output and the unfiltered output from the PHASE DETECTOR
c) The REFERENCE and the LOW-PASS FILTER output
d) None of the above

15. Which portion of a PLL is primarily responsible for determining the lock range?

a) VCO
b) Phase Detector
c) Low-Pass Filter
d) Reference Divider

16. What is the percentage modulation of an FM broadcast transmitter producing 50 KHz deviation?

a) 67%
b) 50%
c) 25%
d) None of the above

17. An FM transmitter is producing 45 KHz of deviation; the information signal is 5 KHz, 10 Vpk. What will happen to the deviation if the information signal is changed to 5 Vpk?

a) The deviation will become 37 KHz
b) The deviation will become 22.5 KHz
c) The deviation will become 75 KHz
d) None of the above

18. How many significant PAIRS of sidebands will be produced by an FM transmitter that is producing 1 KHz of deviation with a 5 KHz deviation rate (information frequency)?

a) 2
b) 1
c) 4
d) None of the above

19. A certain FM transmitter is operating on 29.600 MHz; the unmodulated carrier power is 50 Watts. The maximum permitted deviation is 5 KHz. What power will be delivered to the antenna at 50% modulation?

a) 25 Watts
b) 75 Watts
c) 50 Watts
d) 100 Watts

20. An FM transmitter is operating on 49.860 MHz. Fm = 5 KHz and the deviation is 5 KHz. The unmodulated carrier voltage is 1V. If the output of this transmitter is viewed on a spectrum analyzer, what voltage will be visible at the frequency 49.865 MHz?

a) 440 mV
b) 1000 mV
c) 880 mV
d) None of the above

21. A NARROWBAND FM (NBFM) signal has how many pairs of significant sidebands?

a) 1
b) 2
c) 3
d) 4
e) None of these

22. What is the purpose of guard bands?

a) To reduce distortion on received signals
b) To limit the transmitting distance to line of sight
c) To prevent adjacent channel interference
d) None of the above

23. What is the deviation rate of an FM transmitter when the information frequency Fm = 1 KHz and the deviation is 5 KHz?

a) 1 KHz
b) 5 KHz
c) 6 KHz
d) None of the above

24. What is the total bandwidth allocated for an FM broadcast station in the USA (Including guard bands)?

a) 200 KHz
b) 150 KHz
c) 75 KHz
d) None of the above

25. An FM transmitter is producing 20 KHz of deviation with 1Vpk, 10 KHz information signal. What will happen to the deviation if the information signal is changed to 2Vpk?

a) The deviation will increase to 75 KHz
b) The deviation will decrease to 10 KHz
c) The deviation will increase to 40 KHz
d) None of the above

26. If the frequency at TP "A" in the figure above is 95.300 MHz, what is the MOST LIKELY frequency at TP "D"?

a) 95.300 MHz
b) 93.300 MHz
c) 91.900 MHz
d) None of the above

27. What value should N have in the figure above to get an output frequency of 91.900 MHz? F1=10.000 MHz and R=100.

a) 9190
b) 5620
c) 919
d) 867
e) None of the above

28. Ideally, an FM transmitter converts:

a) Voltage to Frequency
b) Voltage to Current
c) Frequency to Voltage
d) None of the above

29. A 5 MHz crystal oscillator is being driven so that it has 1000 Hz of deviation. This signal is fed into an X3 frequency multiplier. What is the resultant output frequency and deviation?

a) Fout=3 MHz, Deviation=2 KHz
b) Fout=5 MHz, Deviation=3 KHz
c) Fout=15 MHz, Deviation=1 KHz
d) None of the above

30. A 7 MHz crystal oscillator is being driven so that it has 1100 Hz of deviation. This signal is fed into an X5 frequency multiplier. What is the resultant output frequency and deviation?

a) Fout=35 MHz, Deviation=5.5 KHz
b) Fout=21 MHz, Deviation=3.3 KHz
c) Fout=15 MHz, Deviation=1 KHz
d) None of the above

For Exam 3, come prepared to draw a block diagram of a typical superheterodyne receiver, showing typical spectrograms at each of the RF test points. You will also need to be able to design a direct-synthesis PLL at the block diagram level (calculating Fref, Fnatural, N (divisor range), and R (reference divisor). For FM spectral analysis, a Bessel chart will be provided on the last page of the test. You may also use BESSEL.85P (TI85/86) during the test.

Grade Exam!