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1. What is meant by the term "low-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

2. 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

3. 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

4. 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

5. 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

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

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

7. 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

8. The purpose of the frequency converter section of a superhet receiver is to:

a) Keep the output level at the speaker constant, regardless of input signal level changes
b) Eliminate the image response
c) Prevent local oscillator frequency drift
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. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. What deviation corresponds to 100% modulation for FM broadcasts in the USA?

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

18. An FM transmitter is producing 45 KHz of devation; the information signal is 5 KHz, 10 Vpk. What is the modulation index?

a) 9.0
b) 4.5
c) 0.6
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. 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

21. 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

22. 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

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

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

24. 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

25. An FM transmitter converts information voltage into...?

a) Output amplitude changes
b) Output phase changes
c) Output frequency changes
d) None of the above

26. 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

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. 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

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

a) A
b) B
c) C
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!