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1. Why can't TRF receivers be constructed for high-frequency (above 1-2 MHz) use?

a) Insufficent "Q" is available from discrete LC components at these frequencies
b) Transistors and ICs have insufficient gain at these frequencies
c) Detector circuits produce excessive distortion at these frequencies
d) None of the above

2. 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

3. 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

4. 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

5. What is the first step that must take place in receiving a radio signal?

a) Select (Tune desired carrier frequency)
b) Demodulate (Detect)
c) Amplify RF Signal
d) Acquire an RF signal

6. 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

7. 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

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

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

9. What is the name of the amplifier that operates at a constant frequency in a superhet receiver?

a) The audio amplifier
b) The RF amplifier
c) The IF amplifier
d) None of these

10. What frequency should be at TP "B" above if N=1, R=10, F1=1 MHz? Note: F1 is the crystal reference oscillator frequency.

a) 1 MHz
b) 100 KHz
c) 10 KHz
d) None of the above

11. What is the function of a VCO?

a) Converts voltage to frequency
b) Converts frequency to voltage
c) Converts voltage to phase
d) None of the above

12. 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

13. 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

14. 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

15. Given that N=1593, R=1024, and F1 = 10.240 MHz, what will the output frequency Fout of the PLL synthesizer above be?

a) 10.240 MHz
b) 4.9152 MHz
c) 15.930 MHz
d) None of the above

16. What is the maximum deviation permitted for FM broadcasts in the USA?

a) 50 KHz
b) 150 KHz
c) 25 KHz
d) 75 KHz

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

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

18. 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

19. 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

20. A certain FM transmitter is operating on 29.600 MHz; the unmodulated carrier voltage Vc = 50 V. The antenna (load) resistance is 50 Ohms. The maximum permitted deviation is 5 KHz. What power will be delivered to the antenna at 100% modulation?

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

21. A certain FM transmitter operates on 100.1 MHz. The maximum frequency from the transmitter is 100.175 MHz, and the minimum frequency is 100.025 MHz. What is the deviation?

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

22. 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

23. 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

24. What is the approximate (CARSON'S RULE) bandwidth of an FM transmitter with a deviation of 2 KHz and information frequency of 15 KHz?

a) 4 KHz
b) 30 KHz
c) 34 KHz
d) None of the above

25. 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

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. Ideally, an FM transmitter converts:

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

28. 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

29. 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

30. What type of FM transmitter is pictured above?

a) Armstrong WBFM
b) PLL
c) Crosby Frequency-Locked-Loop
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!