Mapa Institute of Technology - ECE 103L

1)A       interconnects LAN having identical protocols at the physical and data link layers.

1. 1. All of these
   2. bridge
   3. router
   4. Gateway

2. Basic speed rate of digital system.
   1. 144 kbps
   2. 1,544 kbps
   3. 64 kbps
   4. 2,048 kbps

3. Calculated the noise figure of the amplifier whose Req equals 2518Ω (RT=600Ω) if its driven by a generator whose output impedance is 50Ω.

A. 39.4

B. 3.94

C. 394

D. 0.394

4.                 is the advantage of the balanced transmission line compared to unbalanced line.

1. Low attenuation
2. Easy installation
3. Low radiation loss
4. Tensile strength

5. Calculate the lowest resonant frequency for a brick partition 120 mm thick, 4m by 2min area with longitudinal wave velocity of 2350 m/s. (Assume that it is supported at its edges.)

1. 10 Hz
2. 20 Hz
3. 30 Hz
4. 40 Hz

6. The noise figure of the first circuit in tandem connection is 10.5 dB while its power gain is 15, what is the overall noise figure if the second circuit has a noise figure of 11 dB?

A. 11.59 dB

B. 11.23 dB

C. 10.79 dB

D. 10.5 dB

7. Waveguide becomes compulsory above what frequencies?

1. Above 3 GHz
2. Above 10 kHz
3. At 300 MHz
4. Above 10 GHz

8. Three identical circuits having 10 dB signal noise-to-noise ratio each are connected in tandem with each other, what is the overall S/N?

A. 5.23 dB

B. 14.77dB

C. 30 dB

D. 40 dB

9. Three identical circuits having 10 dB signal noise-to-noise ratio each are connected in tandem with each other, what is the overall S/N?

A. 5.23 dB

B. 14.77dB

C. 30 dB

D. 40 dB

10. Quarter-wavelength line is used as        .

1. impedance transformer
2. lecher line
3. transmission line
4. harmonic suppressor

11. The length of a Marconi antenna to operate with 985 kHz is        .
    1. 200 ft
    2. 500 ft
    3. 250 ft
    4. 999 ft

12. What is the gain, in dB of a helical antenna with diameter of λ/3, 10 turns at pitch of λ/4, used at 100 MHz?
    1. 16

B. 41.1

C. 31.4

D. 1.25

13. The modulated peak value of a signal is 125 V and the unmodulated carrier value is 85 V. What is the modulation index?

A. 0.47

B. 0.68

C. 0.32

D. 1.47

14. What is the wavelength of a signal at 500 MHz?

A. 0.062 cm

1. 2. 6 meters
   3. 60 cm
   4. 60 meters

15. Not more than             digits make up an international telephone number as recommended by CCITT REC. E. 161.

1. 8
2. 10
3. 11
4. 12

16. If 4 kW in antenna produces 50 μV/m in a receiving antenna, a 15 kW will produce

          .

1. 1. 200 μV/m
   2. 10 μV/m
   3. 100 μV/m
   4. 20 μV/m

17. The maximum intelligibility for voice frequency is located between

A. 250 and 500 Hz

B. 1000 and 3000 Hz

C. 500 and 1000 Hz

D. 3000 and 5000 Hz

18. The frequency of free vibration
    1. Resonant frequency
    2. Natural frequency
    3. Center frequency
    4. Normal frequency

19. A transmitter operating at 30 MHz with 4 W output is connected via 10 m of RG-8A/u cable to an antenna that has an input resistance of 300 ohms. Find the reflection coefficient.

a. 0.71

b. 0.77

c. 0.97

d. 0.76

20. Cellular CDMA system uses what modulation method?

1. GFSK
2. ASK
3. QAM
4. BPSK

21. One of the following is not a bounded media.

1. Coaxial line
2. Two-wire line
3. Waveguide
4. Ocean

22. A microwave-transmitting antenna is 550ft high. The receiving antenna is 200ft high. The minimum transmission distance is

1. 20 mi
2. 33.2 mi
3. 38.7 mi
4. 53.2 mi

23. An instrument designed to measure a frequency-weighted value of the sound pressure level.
    • • i. Sound-level meter

1. 1. 2. Transducer
      3. Sound pressure meter
      4. Sound analyzer

24. 1 Angstrom (A) is equal to             .

a. 10-3 micron

b. 10-10 m

c. 10-6 micron

d. 10-6 m

25. A wide-bandwidth communications systems in which the RF carrier varies according to some predetermined sequence.

1. amplitude compandored single sideband
2. SITOR
3. spread spectrum communication
4. time-domain frequency modulation

26. If N = 250, what is the earth radius K- factor?

a. 1.23

b. 1.29

c. 1.33

d. 1.32

27. An 891 kHz carrier having an amplitude of 80 V is modulated by a 4.5 kHz audio signal having an amplitude of 45 V. The modulation factor is

A. 0.56

B. 0.65

C. 1.78

D. 1.25

28. Which one of the following emission transmits the lower sideband and half of the upper sideband?
    1. A5C
    2. J3E
    3. A3J
    4. A3H

29. What is the effective radiated power of a repeater with 200 watts transmitter power output, 4 dB feline loss, 4 dB duplexer and circulator loss, and 10 dB antenna gain?
    1. 317 W

B. 2000 W

C. 126 W

D. 260 W

30. Combination of modulator, channel, and detector.
    1. Transceiver
    2. Transponder
    3. T/R channel
    4. Discrete channel

31. An amplifier operating over the frequency range of 455 to 460 kHz has a 200 kΩ input resistor. What is the RMS noise voltage at the input to this amplifier if the ambient temperature is 17?C ?

1. 1. 1. 1. 40 μV
         2. 4.0 μV
         3. 400 μV
         4. 4.0 mV

32. What is the polarization of a discone antenna?
    1. 1. 1. 1. 1. Vertical
                2. Horizontal
                3. Circular
                4. Spiral

33. If the antenna increases 3.3 times how much does the radiated power increase?
    1. 1. 1. 1. 1. 3.3 times
                2. 10.89 times
                3. 9.9 times
                4. 6.6 times

34. The transmission of sound from one room to an adjacent room, via common walls, floors or ceilings.
    1. Flanking transmission
    2. Refraction
    3. Reflection
    4. Reverberation

35. The process of impressing intelligence on the carrier is called
    1. modulation
    2. detection
    3. mixing
    4. impression

36. A quarter wave transformer is connected to a parallel wire line in order to match the line to a load of 1000 ohms. The transformer has a characteristic impedance of 316.23 ohms. The distance between centers is 4 inches. What is the percentage reduction in the diameter of the line?

a. 85%

b. 83%

c. 86%

d. 90%

37. Quantity that do not change when a beam of light enters on a medium to another.
    1. Frequency
    2. Wavelength
    3. Direction
    4. Speed

38. What is the standard test tone used for audio measurements?
    1. 100 Hz
    2. 500 Hz
    3. 1000 Hz
    4. 2000 Hz

39. Light leaves a slab of transparent material whose index of refraction is 2 at an angle of refraction of 0 degrees. The angle of incidence is

1. 0 degrees
2. 45 degrees
3. 30 degrees
4. 90 degrees

40. What is the highest frequency that can be sent straight upward and be returned to earth?
    1. MUF
    2. Gyro frequency
    3. Skip frequency
    4. Critical frequency

41. What produces the sidebands on FM?
    1. signal amplitude
    2. carrier harmonics
    3. baseband frequency
    4. broadband frequency

42. Block calls held condition specified the held probability at a time period equal to an average holding time.

1. Erlang B
2. Erlang C
3. Erlang D
4. Poisson

43. A unit of noisiness related to the perceived noise level

1. 1. 1. Noy
      2. Sone
      3. dB
      4. phone

44. The shortest distance measured along the earth’s surface that a skywave is returned to earth.

1. MUF
2. Quarter-wavelength
3. Skip distance
4. Skip zone

SHORT QUESTIONS AND ANSWERS

1.) most commonly used microwave antenna -

2.) When the value of k increases, the effective result is          of the equivalent curvature –

3.) Unit of pitch –

4.)   Not more than          digits make up an international telephone number as recommended by CCITT REC. E. 161. –

5.) Impedance inversion can be obtained by

-

6.) Which of the following is not a common microwave application? –

7.) A waveguide is also a –

8.) Calculated the noise figure of the amplifier whose Req equals 2518Ω (Rt=600Ω) if its driven by a generator whose output impedance is 50Ω. –

9.) Sixteen different levels (symbols) are used to encode binary data. The channel bandwidth is 36 MHz. The maximum channel capacity is –

10.) Which of the following refers to the video signal amplitude that determines the quality of the picture? –

11.) Which of the following is not a low impedance microphone? –

12.) Which one of the following emission transmits the lower sideband and half of the upper sideband? –

13.) The modulated peak value of a signal is 125 V and the unmodulated carrier value is 85 V. What is the modulation index? –

14.) The noise figure of the first circuit in tandem connection is 10.5 dB while its