Excel Review Center
Intensive Final Coaching (IFC)
Instruction: Select the BEST answer. 1.
Calculate the approximate dimensions for a square patch antenna, f or a frequency of 2 GHz, on a substrate with a relative permittivity of 2. A. 50 mm * B. 40 mm
2.
C. 30 mm D. 25 mm
A taxi company uses a central dispatcher, with an antenna at th e top of a 15 m tower, to communicate with taxicabs. The taxi antennas are on the roofs of the cars, approximately1.5m above the ground. Calculate the maximum communication distance between the dispatcher and a taxi. A. 21 km * B. 10.1 km
3.
C. 12 km D. 17.3 km
Find the cutoff frequency for the TE10 mode in an air-dielectric waveguide with an inside cross section of 2 cm by 4 cm. Over what frequency range is the dominant mode the only one that w ill propagate? A. 7.0 GHz B. 15.0 GHz
4.
The GSM cellular radio system uses GMSK in a 200-kHz channel, with a channel data rate of 270.833 kb/s. Calculate the frequency shift between mark and space. A. B. C. D.
5.
135.4165 kHz * 153.4615 kHz 315.4165 kHz 351.4615 kHz
A frequency-hopping spread-spectrum system hops to each of 100 frequencies every ten seconds. How long does it spend on each frequency? A. B. C. D.
7.
C. 143 mm * D. 123 mm
0.01 second per hop 0.1 second second per hop * 0.2 second per hop 0.02 second second per hop
What length of standard RG-8/U coaxial cable would be required to obtain a 45° phase shift at 200 MHz? A. 124 mm * B. 125 mm
8.
Find the characteristic impedance of a coaxial cable using a s olid polyethylene dielectric having ∈r = 2.3, with an inner conductor 2 mm in diameter and an outer conductor 8 mm in inside diameter. A. 54 8 B. 84.5
9.
C. 142 mm D. 140 mm
*
C. 58.4 D. 85.4
Find the maximum dynamic range for a linear PCM system using 16-bit quantizing.
C. 89.88 dB D. 98.08 dB *
10. The North North American TDMA digital cell phone standard transmits at 24.3 kilobaud using DQPSK. What is the channel data rate? A. B.
48.6 kb/s * 45.9 kb/s
C. 46.8 kb/s D. 44.1 kb/s
11. A three-stage three-stage amplifier has stages with the following specifications. Gain and noise figure are given as ratios. Stage Power Noise Gain Figure 1 10 2 2 25 4 3 30 5 Calculate the equivalent noise temperature for the whole amplifier. A. 382 K * B. 364 K
C. 283 K D. 285 K
12. Find the modulation index if a 10-volt carrier is amplitude modulated by three different frequencies, with amplitudes of 1, 2, and 3 volts respectively. A. 0.374 * B. 0.473
C. 0.734 D. 0.300
13. A cell phone transmitter transmitter has a maximum frequency deviation of 12 kHz. Calculate the modulation index if it operates at maximum deviation with a voice frequency of 300 Hz. A. 45 B. 40 *
A series-tuned circuit operating at a frequency of 1 GHz is to be constructed from a shorted section of air-dielectric coaxial cable. What length should be used? A. 133 mm B. 153 mm
6.
C. 3.5 GHz D. 7.5 GHz *
A. 90.88 dB B. 97.98 dB
C. 50 D. 35
14. An FM signal has a frequency deviation of 5 kHz and a modulating frequency of 1 kHz. The signal-to-noise ratio at the input to the receiver detector is 20 dB. Calculate the approximate signal-t onoise ratio at the detector output. A. 34 dB * B. 16 dB
C. 43 dB D. 31 dB
15. A digital communication system uses sampling at 10 kilo samples per second (kSa/s). The receiver filters out all frequencies above 5 kHz. What frequencies appear at the receiver for a 1 kHz signal frequency at the input to the transmitter? A. B. C. D.
1 kHz, 17 kHz and 3 kHz 1 kHz, 13 kHz and 7 kHz 1 kHz, 15 kHz and 5 kHz 1 kHz, 11 kHz and 9 kHz *
16. Calculate the number of of levels ifif the number of bits per sample is 16 (as used in the compact disc audio system). A. 65536 * B. 66553
C. 63556 D. 63655
17. A signal at the input to a mu-law compressor is positive, with its voltage one-half the maximum input voltage. What proportion of the maximum output voltage is produced? A. 0.786Vo B. 0.876Vo *
C. 0.687Vo D. 0.781Vo
Baguio: PiRC Building, Gapuz Centrum II, 80 T. Alonso St., New Lucban CP: 0928 934 1637
FB 20 - EST 18. Convert the 12-bit 12-bit sample 100110100100 into an 8-bit compressed code. A. 11011010 * B. 01011010
C. 11011011 D. 10011010
19. A radio channel has a bandwidth of 10 10 kHz and a signal-to-noise ratio of 15 dB. What is th e maximum data rate than can be transmitted using a code with four possible states? A. 20 kb/s B. 40 kb/s *
C. 30 kb/s D. 50 kb/s
20. A modulator transmits symbols, each of of which has 64 different possible states, 10,000 times per second. Calculate the baud rate and bit rate. A. B. C. D.
5 kbaud and 50 kb/s 10 kbaud and and 60 kb/s * 20 kbaud and 40 kb/s 15 kbaud and 30 kb/s
21. A carrier with an RMS voltage of 2 V and a frequency of 1.5 MHz is modulated by a sine wave with a frequency of 500 Hz and amplitude of 1 V RMS. Write the equation f or the resulting signal. 3
A. v(t) = 2.83 + 1.41 sin (3.14 × 10 t)] 6 sin (9.42 × 10 t) V * 3 B. v(t) = 2.38 + 1.14 sin (3.14 (3.14 × 10 t)] 6 sin (9.42 × 10 t) V 1 C. v(t) = 2.83 + 1.41 sin (3.14 × 10 t)] 5 sin (9.42 × 10 t) V 2 D. v(t) = 2.83 + 1.41 sin (3.14 × 10 t)] 9 sin (9.42 × 10 t) V 22. A modem modem uses 16 different different phase angles and 4 different amplitudes. How many bits does it transmit for each symbol? A. 2 B. 6 *
C. 4 D. 8
23. A voice transmission transmission occupies occupies a channel 30 kHz wide. Suppose a spread-spectrum system is used to increase its bandwidth to 10 MHz. If the signal has has a total signal power of −110 dBm at the receiver input and the system noise temperature referred to the same point is 300 K, calculate the signal-to-noise ratio for both systems. A. B. C. D.
19 dB and -6 dB * 17 dB and and -9 dB 15 dB and and -11 dB 13 dB and and -3 dB
24. A digital communication scheme uses DQPSK. It is to transmit a compressed PCM audio signal which has a bit rate of 16 kb/s. The chipping rate is 10 to 1. Calculate the number of signal changes (symbols) which must be transmitted each second. A. 90 kilobaud B. 60 kilobaud
C. 80 kilobaud * D. 70 kilobaud
25. Find the velocity factor and and propagation propagation velocity for a coaxial cable with a Teflon dielectric (∈r = 2.1). 6
A. 0.69 and 207 x 10 m/s * 6 B. 0.69 and 209 x 10 m/s 6 C. 0.61 and 201 x 10 m/s Manila: CMFFI Bldg. R. Papa St. Tel. 7365291
Excel Review Center
Intensive Final Coaching (IFC) 6
D. 0.63 and 203 x 10 m/s 26. A local loop has a resistance of 1 kΩ, and the telephone connected to it has an off-hook resistance of 200 Ω. Calculate the loop current and the voltage across the telephone when th e phone is on hook. A. B. C. D.
zero and full battery voltage * infinite and zero voltage 10 A and -48 V 5 A and -48 V
27. An FM signal has a deviation of 3 kHz and a modulating frequency of 1 kHz. Its total power is 5 W, developed across a 50 Ω resistive load. The carrier frequency is 160 MHz. Calculate the RMS signal voltage. A. 18.5 V B. 20.1 V
C. 15.8 V * D. 21.6 V
28. A 50-Ω line is terminated in a 25-Ω resistance. Find the SWR. A. 1 B. 0.5
C. 2 * D. 0
29. What frequencies are generated by a telephone using DTMF signalling when the number 9 is pressed? A. B. C. D.
852 Hz and 1477 Hz * 697 Hz and 1477 Hz 941 Hz and 1477 Hz 770 Hz and 1477 Hz
30. Find the propagation loss for a signal at 800 MHz, with a transmitting antenna height of 30 m, over a distance of 10 km, using the free-space model. A. 110.5 dB * B. 124.1 dB
C. 115.0 dB D. 121.3 dB
31. An open-wire line uses wire with a diameter of 2 mm. What should the wire spacing be for an impedance of 150 Ω? A. 1.5 mm B. 3.5 mm *
C. 2.5 mm D. 4.5 mm
32. A resistor has a noise temperature of 300 K. Find its noise power density. A. B. C. D.
−19
4.14 × 10 W/Hz −23 4.14 × 10 W/Hz −21 4.14 × 10 W/Hz * −18 4.14 × 10 W/Hz
33. A generator sends 50 mW down a 50-Ω line. The generator is matched to the line but the load is not. If the coefficient of reflection is 0.5, how much power is reflected and how much is dissip ated in the load? A. B. C. D.
12.5 mW and 37.5 mW * 15.0 mW and 35.5 mW 25.1 mW and 56.1 mW 10.5 mW and 35.5 mW
34. A transmitter supplies 50 W to a load through a line with an SWR of 2. Find the power absorbed by the load. A. 44.4 W * B. 34.4 W
C. 54.3 W D. 64.4 W
FB 20 - EST
35. A transmission line is specified to have a loss of 4 dB/100 m at 800 MHz. Find the loss in decibels of 130 m of this cable. A. 3.2 dB B. 5.2 dB *
C. 1.2 dB D. 2.2 dB
36. A waveguide has a cutoff frequency for the dominant mode of 10 GHz. Two signals with frequencies of 12 and 17 GHz respectively propagate down a 50 m length of the guide. Calculate the difference in arrival time for the two. A. 95.5 s B. 95.5 ns *
C. 95.5 ms D. 95.5 ps
2
2
C. 76.9 nW/m 2 D. 87.1 nW/m
38. A transmitter has a power output of 150W at a carrier frequency of 325MHz. It is connected to an antenna with a gain of 12 dBi. The receiving antenna is 10 km away and has a gain of 5 dBi. Calculate the power delivered to the receiver, assuming free-space propagation. Assume also that there are no losses or mismatches in the system. A. -33.9 dBm * B. -43.3 dBm
C. -39.3 dBm D. -53.5 dBm
39. Find the propagation loss for a signal at 800 MHz, with a transmitting antenna height of 30 m, over a distance of 10 km, using the mobile-propagation model. A. 159.5 dB * B. 165.0 dB
C. 195.5 dB D. 175.1 dB
40. An AM transmitter has a carrier power output of 50W.What would be the total power produced with 80% modulation? A. 56 W B. 46 W
C. 66 W * D. 76 W
41. An automobile travels at 60 km/hr. Find the time between fades if the car uses a cell phone at 800 MHz. A. 12.1 ms B. 11.2 ms *
C. 10.1 ms D. 14.3 ms
42. A metropolitan area of 1000 square km is to be covered by cells with a radius of 2 km. How many cell sites would be required, assuming hexagonal cells? A. 83 B. 73 *
C. 93 D. 63
C. 80 mm * D. 90 mm
45. A pyramidal horn has an aperture (opening) of 58 mm in the E plane and 78 mm in the H plane. It operates at 10 GHz. Calculate its gain in dBi. A. 15.8 dBi * B. 13.9 dBi
C. 18.5 dBi D. 12.9 dBi
46. A resistor at a temperature of 25°C is connected across the input of an amplifier with a bandwidth of 50 kHz. How much noise does the r esistor supply to the input of the amplifier? A. 0.206 fW * * B. 0.206 W
37. A power of 100W is supplied to an isotropic radiator. What is the power density at a point 10 km away? A. 79.6 nW/m * 2 B. 97.1 nW/m
A. 60 mm B. 70 mm
C. 0.206 pW D. 0.206 aW
47. Citizens’ band radio channels are 10 kHz wide. What is the maximum modulation frequency that can be us ed if a signal is to remain entirely within its assigned channel? A. 5 kHz * B. 3 kHz
C. 10 kHz D. 15 kHz
48. Calculate the minimum data rate needed to transmit audio with a sampling rate of 40 kHz and 14 bits per sample. A. 460 kb/s B. 640 kb/s
C. 560 kb/s * D. 650 kb/s
49. A signal would have a bandwidth of 200 kHz and a signal-to-noise ratio of 20 dB if transmitted without spreading. It is spread using a chipping rate of 50:1. Calculate its bandwidth and signal-tonoise ratio after spreading. A. B. C. D.
10 MHz and 3 dB * 5 MHz and 1.5 dB 7.5 MHz and 7 dB 1 MHz and 3.5 dB
50. A transmitter has a power output of 10 W at a frequency of 250 MHz. It is connected by 20 m of a transmission line having a loss of 3 dB/100 m to an antenna with a gain of 6 dBi. The receiving antenna is 25 km away and has a gain of 4 dBi. There is negligible loss in the receiver feedline, but t he receiver is mismatched: the antenna and line are designed for a 50 Ω impedance, but the receiver input is 75 Ω. Calculate the power delivered to t he receiver, assuming free-space propagation. A. -51.9 dBm B. -61.9 dBm
C. -59.1 dBm * D. -69.1 dBm
< < < Nothing Follows > > >
43. Calculate the free-space path loss at a frequency of 1 GHz, for each of the following paths, to a point on the earth directly under the satellite fr om a LEO satellite at an altitude of 500 km. A. 164.1 dB B. 143.3 dB
C. 146.4 dB * D. 145.2 dB
44. A helical antenna with 8 turns is to be constructed for a frequency of 1.2 GHz. Calculate the optimum diameter.
Baguio: PiRC Building, Gapuz Centrum II, 80 T. Alonso St., New Lucban CP: 0928 934 1637
Manila: CMFFI Bldg. R. Papa St. Tel. 7365291
