EET368 Practice Test III

Instructions: There are 30 questions on this test. It is written in a style very similar to the REAL exam #3. Choose the best answer from among those given. Click the GRADE button on the bottom of the form when you want the exam graded.

Note: You can practice this test as many times as you desire; the system will cook you up a fresh batch of questions each time you access this page.

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1. 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

2. What section of a superheterodyne receiver is responsible for attenuation of the image frequency?

a) Detector
b) Preselector
c) Local Oscillator
d) None of these

3. Which of the following specifies the most sensitive receiver? All the units have the same bandwidth. Hint: Convert all into absolute power units.

a) 1 uV into 75 Ohms for better than 10 dB S/N ratio
b) 0.5 uV into 50 Ohms for better than 10 dB S/N ratio
c) -120 dBm for better than 10 dB S/N ratio
d) -110 dBm for better than 10 dB S/N ratio

4. 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

5. The ability of the preselector and local oscillator stages to keep a constant difference of F(if) in a superhet receiver is referred to as:

a) AGC
b) Detection
c) Alignment
d) Tracking

6. 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

7. The two signal components that are produced in a diode-type AM detector circuit are:

a) The upper and lower sidebands
b) A DC level and the AC information signal
c) The carrier frequency and sidebands
d) None of these

8. What is meant by the term "high-side injection?"

a) The local oscillator operates with a large AC output signal
b) The IF amplifier uses negative-bias to produce AGC
c) The local oscillator operates above the frequency of the RF carrier
d) None of the above

9. 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

10. Which part of a PLL converts voltage changes into frequency changes?

a) Phase Detector
b) Low Pass Filter
c) VCO
d) None of the above

11. 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

12. 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

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

F1 = 10.000 MHz
"A" = 100 KHz (5 Vpp square wave)
"B" = 90 KHz (5 Vpp square wave)
VCO Control Voltage = 7.9 V (Steady DC); Vcc = 8.0 V
"D" = 118.536 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. 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

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 approximate (CARSON'S RULE) bandwidth of an FM transmitter with a deviation of 5 KHz and information frequency of 1 KHz?

a) 10 KHz
b) 2 KHz
c) 15 KHz
d) None of the above

17. A certain FM transmitter operates on 95.3 MHz. The maximum frequency from the transmitter is 95.325 MHz, and the minimum frequency is 95.275 MHz. What is the deviation?

a) 50 KHz
b) 150 KHz
c) 25 KHz
d) None of the above

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

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

19. 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

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. The information voltage is 3Vpk. What MINIMUM information voltage will cause the 49.860 frequency component (as viewed on a spectrum analyzer) to become ZERO?

a) 3.24 Vpk
b) 5.00 Vpk
c) 7.20 Vpk
d) None of the above

21. 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 49.860 MHz?

a) 440 mV
b) 770 mV
c) 880 mV
d) None of the above

22. 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

23. How many significant PAIRS of sidebands will be produced by an FM transmitter that is producing 2 KHz of deviation with a 1 KHz deviation rate (information frequency)?

a) 2
b) 1
c) 3
d) 4

24. 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

25. What type of the transmitters convert input (information) amplitude changes into output carrier frequency changes?

a) FM
b) AM
c) PM
d) None of the above

26. Which class of amplifier is generally preferred for power amplification in FM transmitters?

a) A
b) B
c) C
d) None of the above

27. What type of FM transmitter is pictured above?

a) Armstrong WBFM
b) PLL
c) Crosby Frequency-Locked-Loop
d) None of the above

28. Why is it possible to amplify FM signals in a class C amplifier?

a) The maximum power is no more than twice the unmodulated power
b) The power in an FM signal is constant
c) The bandwidth of FM signals quite small, less than 10 KHz
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. 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

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.

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