EET 412 2017-1 1. The number of different possible binary PCM values that can be encoded with 5-bit words is (a) 16 (b) 5 (c) 64 (d) 32 2. An analog signal is to be encoded with at least 2000 values. The minimum number of bits for each word is (a) 12 (b) 11 (c) 10 (d) 9 Problems 3, 4, and 5 refer to a 10-bit ADC with unipolar encoding, rounding, and a full-scale voltage of 20 V. 3. The closest value to the step size (in mV) is (a) 40 (b) 20 (c) 10 (d) 5 (c) 20 (d) 10 4. The closest value to the maximum error (in mV) is (a) 5 (b) 2.5 5. The closest value to the maximum quantization level (in volts) is (NOTE: Higher accuracy is required.) (a) 19.98 (b) 19.99 (c) 19.96 (d) 19.97 Problems 6 and 7 refer to a 10-bit ADC using bipolar encoding, rounding, and a range from -10 V to 10 V. 6. The closest value to the step size (in mV) is (a) 5 (b) 10 (c) 20 (d) 40 (c) 20 (d) 2.5 7. The closest value to the maximum error (in mV) is (a) 10 (b) 5 8. The peak-to-peak value of an analog signal to be converted to binary PCM is 10 V. Determine the minimum number of signal bits required in each word if the peak error cannot exceed 15 mV and rounding is employed. (a) 7 (b) 8 (c) 9 (d) 10 9. A D/A converter in a digital communication system processes the 4-bit digital word 1001. If 1 LSB represents a value of 0.5 V, determine the analog value (in volts) corresponding to the word. (a) 9 (b) 11 (c) 4.5 (d) 2.5 10. A mu-law compression CODEC has a maximum output voltage of 10 V, a maximum input voltage of 10 V, and = 255. Determine the output voltage (in volts) when the input voltage is 5 V. (a) 1.24 (b) 5 (c) 2.5 Page 1 of 7 (d) 8.76 11. The acronym for the line code in which a space causes a change in the pulse level, but a mark does not cause a change in the level is (a) RZ (b) NRZ-L (c) NRZ-M (d) NRZ-S 12. The acronym for the line code in which a transition occurs at the beginning of each bit interval and a second transition occurs in the middle of the pulse interval when the data value is a mark is called (a) Biphase-L (b) Biphase-M (c) Biphase-S (e) NRZ-M 13. The acronym for the digital modulation method in which a mark and a space are encoded as two separate frequencies is (a) FSK (b) DPSK (c) QPSK (e) QAM 14. The acronym for the digital modulation method in which a mark and a space are encoded as two different phase shifts is (a) BPSK (b) QPSK (c) FSK (d) ASK 15. The acronym for the digital modulation method in which the data train is first converted into either NRZ-M or NRZ-S prior to modulating a carrier is (a) DPSK (b) ASK (c) FSK (d) ASCII Problems 16 through 20 refer to a baseband NRZ-L baseband signal having a data rate of 8 Mbits/s. In each case the baseband signal modulates an RF carrier and the objective is to determine the theoretical RF bandwidth. 16. The minimum transmission bandwidth (in MHz) for ASK is (a) 4 (b) 8 (c) 16 (d) 32 17. The minimum transmission bandwidth (in MHz) for BPSK is (a) 8 (b) 4 (c) 2 (d) 16 18. The minimum transmission bandwidth (in MHz) for FSK if the two frequencies are 1 GHz and 1.005 GHz is (a) 1000 (b) 8 (c) 5 (d) 13 19. The minimum theoretical transmission bandwidth (in MHz) for DPSK is (a) 4 (b) 8 (c) 16 (d) 32 20. The minimum theoretical transmission bandwidth (in MHz) for QPSK is (a) 4 (b) 8 (c) 16 Page 2 of 7 (d) 32 A baseband channel has a bandwidth of 10 kHz. It will serve as the basis for Problems 21 through 25. The values in all cases are based on theoretical bounds. 21. Determine the maximum symbol rate (in kbaud) if the channel is noise free. (a) 5 (b) 10 (c) 20 (d) 40 22. Determine the channel capacity (in kbits/s) for binary encoding if the channel is noise free. (a) 40 (b) 5 (c) 10 (d) 20 23. Determine the channel capacity (in kbits/s) for 16-level encoding if the channel is noise free. (a) 20 (b) 40 (c) 80 (d) 160 24. Determine the channel capacity (in kbits/s) for 32-level encoding if the S/N ratio is 11.761 dB. (a) 20 (b) 40 (c) 80 (d) 100 25. Determine the channel capacity (in kbits/s) for 32-level encoding if the S/N ratio is 40 dB. (a) 133 (b) 40 (c) 80 (d) 100 A baseband digital communications system is to be designed to transmit 40 kbits/s. The baseband channel bandwidth is 4 kHz. Problems 26 through 28 deal with this system. 26. Determine the minimum number of bits per baud (bits per signaling element) required. (a) 1 (b) 2 (c) 5 (d) 20 (c) 10 (d) 5 27. Determine the number of possible levels required. (a) 32 (b) 64 28. Determine the minimum signal-to-noise ratio (in decibels). (a) 1023 (b) 30.1 (c) 15.1 (d) 60.1 29. A coding scheme for a QAM system has 8 possible phase values and the amplitude at each phase state may assume 8 possible amplitudes. Determine the possible number of distinct code words that can be generated. (a) 8 (b) 64 (c) 16 (d) 88 30. For the scheme of the preceding problem, determine the number of bits per baud. (a) 8 (b) 64 (c) 16 Page 3 of 7 (d) 6 31. A data system in which transmission can take place simultaneously in both directions is called (a) half-duplex (b) simplex (c) full-duplex (d) bipolar 32. A data system in which transmission is always in one direction is called (a) unipolar (b) full-duplex (c) half-duplex (d) simplex 33. A data system in which transmission can be in either direction, but not simultaneously is called (a) full-duplex (b) simplex (c) half-duplex (d) synchronous 34. When you perform word processing on your computer, the mode of transmission could be characterized as (a) synchronous (b) asynchronous (c) unipolar (d) bipolar 35. When talking with a friend are engaged in an exciting conversation on the telephone, the mode of transmission could be characterized as (a) full-duplex (b) half-duplex (c) simplex (d) synchronous (c) 1000111 (d) 1110110 36. The ASCII code for the number 7 (MSB first) is (a) 0111001 (b) 0110111 37. Determine the letter, number, or symbol for the ASCII value 1001011 (MSB first). (a) G (b) I (c) ; (d) K 38. Assume that the character of Problem 37 is to be transmitted in the normal serial form with start bit, 7-bit character with LSB first, an odd parity bit, and a stop bit. Indicate which of the bit patterns below describes the process, with the start bit being the first one, the stop bit being the last one, and positive logic. (a) 0110100101 (b) 0110100111 (c) 0110100011 (d) 0110101111 39. The old Bell 202 FSK standard utilizes 1200 Hz for a space and 2200 Hz for a mark. Determine the required transmission bandwidth (in Hz) based on a data rate of 1200 bits/s. (a) 1000 (b) 1200 (c) 2200 (d) 3400 40. An old format used with the baudot code for some teletype machines was a start bit, the five-bit baudot code, and a stop bit for each character. All bits were 22 ms in length except that the stop bit was 1.42 times the width of the other bits. A word is considered as 5 characters plus a space equal in length to a character. A rule-of-thumb was that the data rate was X words per minute. Determine the approximate value for X. (a) 20 (b) 60 (c) 6 Page 4 of 7 (d) 100 41. The two inputs to an ideal mixer are cos(6283t / 2) and 2cos(6283t / 2) , both expressed in volts. The output of the mixer is applied as the input to an ideal low-pass filter with a cutoff frequency of 1500 Hz. Determine the output of the low-pass filter (in volts). (a) 1 (b) 0 42. The two inputs to an ideal mixer are (c) cos(3142t ) (d) cos(6284t ) cos(6283t / 2) and 2sin(6283t / 2) , both expressed in volts. The output of the mixer is applied as the input to an ideal low-pass filter with a cutoff frequency of 1500 Hz. Determine the output of the low-pass filter (in volts) (a) 1 (b) 0 (c) (d) cos(3142t ) sin(6283t ) 43. An advantage of DPSK over BPSK is (a) DPSK requires fewer bits for encoding a word than BPSK (b) The bandwidth required is less for a given data rate. (c) The error rate is less than that of BPSK. (d) DPSK acts as its own reference for demodulation. 44. For a given transmission bandwidth, the theoretical data rate for QPSK compared with BPSK is (a) the same (b) half as great (c) twice as great (d) four times as great 45. For a given data rate, the theoretical bandwidth required for QPSK compared with BPSK is (a) the same (b) half as great (c) twice as great (d) four times as great 46. MP3 is a patented digital audio format using a form of lossy data compression. It reduces the data storage by a factor of about 1/11. The standard for most regular commercial music CD's is a sampling rate of 44.1 ksamples/s for each of two channels (stereo) and each sample has 16 bits. Determine the approximate data rate (in kbits/s) for MP3. (a) 128 (b) 64 (c) 256 (d) 1024 47. Several years ago, the Virginia Symphony led by Conductor JoAnn Falleta gave a magnificent performance of Mahler's Symphony #2 (Resurrection). Let's assume that the performance lasted 75 minutes and that it was digitally recorded in stereo using a sampling rate of 44.1 ksamples/s for each channel and that each sample was represented by 16 bits. Neglecting any error detection and correction bits, determine the total number of bytes required to encode the complete concert. Note: G = 1e9, M = 1e6, 1 byte = 8 bits. (a) 794 Mbytes (b) 6.35 Gbytes (c) 50.8 Gbytes (d) 397 Gbytes Problems 48, 49, and 50 refer to a 5-M resistance in a bandwidth of 200 MHz at a temperature of 290 K. 48. Determine the available one-sided power spectral density (in W/Hz) for the resistance. (a) 1.38x10-23 (b) 16x10-21 (c) 800x10-5 49. Determine the available noise power (in W) contained in the resistance.. Page 5 of 7 (d) 4x10-21 (a) 4x10-21 (b) 20x10-15 (c) 16x10-6 (d) 800x10-15 50. Determine the rms open-circuit noise voltage (in mV). (a) 4 (b) 0.016 (c) 16 (d) 20 51. Two resistances of equal value and at equal temperature are connected in series and the net rms noise voltage across the combination is 2 V. Determine the rms noise voltage (in V) across the combination if the resistors are connected in parallel, assuming that the bandwidth and temperature remain the same. (a) 0.5 (b) 1.414 (c) 0.707 (d) 1 52. A noise generator has an equivalent noise temperature of 50,000 K. Determine the available noise power spectral density (in W/Hz). (a) 0.5 (b) 4x10-21 (c) 690x10-21 (d) 50,000 53. A noisy receiver has an effective noise temperature of 1000 K. A preamplifier having a gain of 20 dB and a noise temperature of 50 K is added to the receiver at the input. Determine the new effective noise temperature (in kelvin) referred to the input of the preamplifier. (a) 100 (b) 50 (c) 60 (d) 1000 54. A receiver has a noise figure of 3.01dB. A coaxial cable having a loss of 6.02 dB and a physical temperature of 290 K is connected between the receiver input and an antenna. Determine the noise figure (in dB) of the receiver referred to the input of the cable. (a) 3.01 (b) 2 (c) 8 (d) 9.03 55. A signal has frequency components from dc to 10 kHz. It is to be sampled and each sample is to be converted to 8-bit digital words. Determine the theoretical minimum data rate (in kbits per second) that would permit recovery. (a) 10 (b) 80 (c) 160 (d) 20 56. The signal of the preceding problem is to be sampled at a rate that would be sufficient to provide a guard band of 5 kHz. Determine the minimum sampling rate (in samples per second) (a) 25 (b) 5 (c) 20 (d) 40 57. Consider the 8-bit NRZ-L stream 10110101. Assume that the preceding bit prior to the first bit in the output stream is a zero. Indicate the resulting bit stream based on NRZ-S encoding after the initial bit. (a) 11011001 (b) 01110011 (c) 10001100 (d) 01010110 58. For the bit stream of the preceding problem (10110101), determine the resulting bit stream based on NRZ-M encoding after the initial bit. Again, assume that the initial bit prior to the first bit in the output stream is a zero. (a) 01110011 (b) 10001100 (c) 11011001 (d) 10110100 59. Which one of the following is the major source of external noise in the AM broadcast band in a very rural area? (a) atmospheric (b) galactic (c) thermal (d) shot 60. On my honor as an ODU student, I certify that in completing this examination, (a) I have received help from one or more students enrolled in the class. Page 6 of 7 (b) I have given help to one or more students enrolled in the class. (c) I have neither given nor received help from any other person. (d) I have received help from one or more persons not enrolled in the class. Reminder: Please transfer all answers to the special answer sheet provided and send it as an attachment to wstanley@odu.edu . Please do not alter the spacing on the answer sheet. You need not return this document. Page 7 of 7