ECT261 Practice Test I

Instructions: There are 25 questions on this test. It is written in a style very similar to the REAL exam #1. 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. What type of filter is used to separate radio stations in a receiver?

a) Bandpass
b) Highpass
c) Lowpass
d) None of the above

2. A certain transmitter's antenna is 5/8 wavelength long and measures 49.213 inches. What is the actual operating frequency of this transmitter? (1 inch = 2.54 cm).

a) 25 MHz
b) 50 MHz
c) 75 MHz
d) 150 MHz
e) None of the above

3. Why can't audio frequencies be directly transmitted through an antenna system?

a) The antenna required would be too long
b) Too much power would be required
c) The receiver would distort the information waveform
d) None of the above

4. Which of these describes demodulation?

a) Recovering information from a carrier wave
b) Placing information onto a carrier wave
c) Controlling the frequency of a carrier wave
d) None of the above

5. Why is modulation and carrier transmission necessary in radio?

a) To keep antenna lengths reasonable
b) To allow stations to be separated by radio receivers
c) Both A and B
d) None of these

6. What is the wavelength of a 1 MHz signal?

a) 100 Meters
b) 200 Meters
c) 300 Meters
d) None of the above

7. A certain transmitter's antenna is 1/4 wavelength long and measures 29.528 inches. What is the actual operating frequency of this transmitter? (1 inch = 2.54 cm).

a) 25 MHz
b) 50 MHz
c) 100 MHz
d) None of the above

8. What is the wavelength of a 600 MHz signal?

a) 1 Meter
b) 0.5 Meter (50 cm)
c) 0.75 Meter
d) None of the above

9. What frequency is two octaves above 1 KHz?

a) 2 KHz
b) 3 KHz
c) 5 KHz
d) None of the above

10. The horizontal axis of a spectrum analyzer is labeled in what units?

a) Time - Seconds
b) Resistance - Ohms
c) Frequency - Hz
d) None of the above

11. What is the frequency of the 3rd harmonic for the signal above?

a) 1 KHz
b) 2 KHz
c) 3 KHz
d) None of these

12. What is the relationship of the 2 KHz frequency component to the 1 KHz component in the figure above?

a) The 2 KHz signal is twice the amplitude of the 1 KHz signal
b) The 2 KHz is a distorted form of the 1 KHz signal
c) The 2 KHz signal is the 2nd harmonic of the 1 KHz signal
d) None of the above

13. Which of these could be classified as an external noise source?

a) Shot Noise
b) Atmospheric noise
c) Flicker Noise
d) None of the above

14. What signal to noise ratio, in dB, will result if a system has 1 mV of noise and 1000 mV of signal voltage?

a) 10 dB
b) 20 dB
c) 60 dB
d) None of the above

15. Noise can best be defined as:

a) Any undesired signal within a system
b) Pulses appearing at the output of a system
c) Distortion at the output of a system
d) None of the above

16. What noise voltage will be generated across a 100K resistor at room temperature (24 degrees Celsius) if the circuit's bandwidth is 1 MHz? (k=1.38 x 10-23 J/K)

a) 40.5 uV
b) 0.5 uV
c) 20 uV
d) None of the above

17. An AM signal was measured on an oscilloscope. The readings were Vmax=400 V, and Vmin = 100V. What is the percent modulation?

a) 33.3%
b) 60 %
c) 75 %
d) None of the above

18. What bandwidth will be required to transmit a 2 KHz sine-wave tone on an AM carrier wave if the carrier frequency is 118 MHz?

a) 10 KHz
b) 4 KHz
c) 8 KHz
d) None of these

19. An AM transmitter is operating on a carrier frequency (Fc) of 10.000 MHz, with 5000 volts of carrier (Vc). The transmitter is operating at 70% modulation. What is the voltage in the upper side band?

a) 3500 V
b) 2750 V
c) 2000 V
d) 1750 V

20. What is the information frequency in the AM signal pictured above?

a) 1 KHz
b) 2 KHz
c) 4 KHz
d) 5 KHz

21. A certain AM transmitter produces 16W of power into a 50 Ohm load with no modulation. What total power will be produced at 50% modulation?

a) 17 W
b) 18 W
c) 20 W
d) None of the above

22. A certain AM transmitter produces 10W of power into a 50 Ohm load with no modulation. What total power will be produced at 100% modulation?

a) 15 W
b) 20 W
c) 30 W
d) None of the above

23. What is the total bandwidth of the AM signal pictured above?

a) 500 Hz
b) 1 KHz
c) 2 KHz
d) 4 KHz

24. If the load resistance RL is 50 Ohms, what is the total power of the AM signal above?

a) 200 Watts
b) 204 Watts
c) 250 Watts
d) None of the above

25. An AM transmitter is operating on a carrier frequency (Fc) of 1500 KHz, with 50 volts of carrier (Vc). The transmitter is operating at 90% modulation. What is the intelligence voltage (Vm or Vi)?

a) 50 V
b) 40 V
c) 45 V
d) None of these


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