This document contains 40 multiple choice questions about communications concepts like amplitude modulation, frequency modulation, noise, and signal processing. The questions cover topics such as calculating modulation indices, bandwidth requirements, transmitter power levels, and noise figures of amplifiers. They assess understanding of fundamental electronics and signal processing principles as applied to radio communications systems.
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This document contains 40 multiple choice questions about communications concepts like amplitude modulation, frequency modulation, noise, and signal processing. The questions cover topics such as calculating modulation indices, bandwidth requirements, transmitter power levels, and noise figures of amplifiers. They assess understanding of fundamental electronics and signal processing principles as applied to radio communications systems.
This document contains 40 multiple choice questions about communications concepts like amplitude modulation, frequency modulation, noise, and signal processing. The questions cover topics such as calculating modulation indices, bandwidth requirements, transmitter power levels, and noise figures of amplifiers. They assess understanding of fundamental electronics and signal processing principles as applied to radio communications systems.
Copyright:
Attribution Non-Commercial (BY-NC)
Available Formats
Download as DOC, PDF, TXT or read online from Scribd
This document contains 40 multiple choice questions about communications concepts like amplitude modulation, frequency modulation, noise, and signal processing. The questions cover topics such as calculating modulation indices, bandwidth requirements, transmitter power levels, and noise figures of amplifiers. They assess understanding of fundamental electronics and signal processing principles as applied to radio communications systems.
Copyright:
Attribution Non-Commercial (BY-NC)
Available Formats
Download as DOC, PDF, TXT or read online from Scribd
Download as doc, pdf, or txt
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Problem Solving (Communications) 6.
Compute for the noise voltage
applied to the receiver input in 1. In the equation of the instantaneous Problem 5. voltage as a function of time a. 5.4 mV e(t ) = 5sin(5000t + 30) , what is the b. 5.4 μV amplitude of the wave in rms? c. 5.4 nW a. 5 volts d. 5.4 pV b. 30 volts 7. A diode noise generator is required c. 3.54 volts to produce 10 μV of noise in a d. None of the above receiver with an input impedance of 2. What is the frequency of the signal 75 Ω, resistive, and a noise power in Problem 1? bandwidth of 200 kHz. (These values a. 5000 Hz are typical of FM broadcast b. 5 Hz receivers.) What must be the current c. 30 Hz through the diode be? d. 796 Hz a. 0.133 μA 3. Calculate the wavelength in free b. 276 mA space corresponding to a frequency c. 7.5 μA of CB radio band. d. 13.3 nA a. 300 m 8. Two resistors (R1 and R2) are in b. 11.1 m series at two different temperatures c. 7.5 cm (R1 = 300 K and R2 = 400K). Find d. 3 cm the total noise voltage produced at 4. A receiver has a noise power the load (RL=300 Ω), over a bandwidth of 10 kHz. A resistor that bandwidth of 100 kHz. matches the receiver input a. 779 mV impedance is connected across its b. 779 μV antenna terminals. What is the noise c. 779 nV power contributed by that resistor in d. 779 pV the receiver bandwidth, if the resistor 9. Find the noise power produced by has a temperature of 27ºC? the circuit in Problem 8. a. 4.14 x 10-17 W a. 0.605 μW b. 4.14 x 10-18 W b. 5.06 nW c. 4.14 x 10-16 W c. 0.6 pW d. 4.14 x 10-15 W d. 0.506 fW 5. A 300 Ω resistor is connected across 10. A receiver produces a noise power of the 300 Ω antenna input of a 200 mW with no signal. The output television receiver. The bandwidth of level increases to 5 W when a signal the receiver is 6 MHz, and the is applied. Calculate (S+N)/N as a resistor is at room temperature. Find power ratio. the noise power applied to the a. 25 receiver input? b. 0.10 a. 24.2 nW c. 0.04 b. 24.2 pW d. 5.2 c. 24.2 fW d. 24.2 μW 11. The signal power at the input to an a. 145.99635 MHz amplifier is 100 μW and the noise b. 146.00219 MHz power is 1 μW. At the output, the c. 146.01542 MHz signal power is 1 W and the noise d. 145.98654 MHz power is 30 mW. What is the 17. Find the minimum transmit amplifier noise figure, as a ratio? frequency for Problem 16. a. 100 a. 145.99635 MHz b. 33.3 b. 146.00219 MHz c. 3 c. 146.01542 MHz d. None of the above d. 145.98654 MHz 12. The signal at the input of an 18. Sine-wave signals with frequencies amplifier has an S/N of 42 dB. If the of 10 MHz and 11 MHz are applied amplifier has a noise figure of 6 dB, to a square-law mixer. What what is the S/N at the output (in dB)? frequencies appears at the output? a. 48 dB a. 22 MHz and 20 MHz b. 7 dB b. 21 MHz and 1 MHz c. 36 dB c. 10 MHz and 11 MHz d. None of the above d. All of the above 13. An amplifier has a noise figure of 2 19. A PLL has a VCO with a free- dB. What is the equivalent noise running frequency of 12 MHz. As temperature? the frequency of the reference input a. 169.6 K is gradually raised from zero, the b. 156.6 K loop locks at 10 MHz and comes out c. 126.7 K of lock again at 16 MHz. Find the d. 196.7 L capture range of the PLL. 14. An RF amplifier has a tank a. 8 MHz consisting of L=25 μH and C = 50 b. 4 MHz pF. Find the operating frequency. c. 14 MHz a. 300 kHz d. 16 MHz b. 4.50 MHz 20. Find the lock range of the PLL in c. 1.50 MHz Problem 19. d. 600 kHz a. 8 MHz 15. What is the bandwidth needed for b. 4 MHz Problem 14, assume the Q is 15? c. 14 MHz a. 300 kHz d. 16 MHz b. 4.50 MHz 21. Find the modulation index if a 10 V c. 1.50 MHz carrier is amplitude-modulated by d. 600 kHz thee different frequencies with 16. A portable radio transmitter has to amplitudes of 1 V, 2V and 3V operate at temperatures from -5ºC to respectively. 35ºC. If its signal is derived from a a. 0.1 crystal oscillator with a temperature b. 0.2 coefficient of +1 ppm/degree C and c. 0.374 it transmits at exactly 146 MHz at d. 0.3 20ºC, find the maximum transmitting frequency? 22. Calculate the modulation index if the 28. An AM broadcast station operates at maximum voltage is 150 mV and the its maximum allowed total output of minimum voltage is 70 mV. 50,000 W and at 85% modulation. a. 0.364 How much of the transmitted power b. 2.75 contains the intelligence? c. 0.47 a. 36.73 kW d. 2.14 b. 13.3 kW 23. CB radio channels are 10 kHz apart. c. 6.65 kW What is the maximum modulation d. None of the above frequency that can be used if a signal 29. For an AM DSB-FC transmitter with is to remain entirely within its an unmodulated carrier power of 500 assigned channel? W that is modulated simultaneously a. 10 kHz by four tones, m1=0.1,m- b. 5 kHz 2=0.2,m3=0.4, and m4=0.5, determine c. 270 kHz the total modulation index? d. None of the above a. 0.91 24. An AM broadcast transmitter has a b. 1.2 carrier power output of 50 kW. What c. 0.68 total power would be produced with d. 0.86 80% modulation? 30. Determine the total sideband power a. 66 kW of Problem 29. b. 75 kW a. 615.6 W c. 80 kW b. 115.6 W d. 16 kW c. 57.8 W 25. What is the modulation index for an d. None of the above AM having Vmax and Vmin of 2.6 31. Determine the total transmitted amd 0.29, respectively? power of Problem 29. a. 0.1115 a. 615.6 W b. 0.7793 b. 115.6 W c. 8.9655 c. 57.8 W d. 1.2511 d. None of the above 26. Determine the bandwidth of an AM 32. An antenna current of an AM signal modulated by a 5-kHz tone. transmitter is 11 A when a. 5 kHz unmodulated but increases to 14 A b. 10 kHz when modulated. Find the c. 15 kHz percentage of modulation. d. 20 kHz a. 111.34% 27. An AM transmitter radiates 100 W at b. 89.56% 100% modulation. How much power c. 65% is required for the carrier? d. 50% a. 66.67 W 33. An AM transmitter has a carrier b. 150 W voltage of 50 Vrms at a carrier c. 33.33 E frequency of 10 MHz. it is d. None of the above modulated at 75% by a 1-kHz sine wave. How much is the total rms voltage transmitted? a. 66.67 Vrms deviation is 50 kHz while its audio b. 150 Vrms frequency is 10 kHz? c. 56.6 Vrms a. 5 d. 96 Vrms b. 0.2 34. An Am transmitter must transmit c. 0.66 39.9-kW PEP. It maintains an d. 1.5 average current of 1.5 A and an 80% 40. Determine the approximate plate efficiency. Determine the bandwidth of an FM signal average output power at 100% modulated by a 15-kHz tone whose modulation. frequency deviation is 45 kHz. a. 15 kW a. 120 kHz b. 10 kW b. 180 kHz c. 39.9 kW c. 240 kHz d. 50 kW d. 60 kHz 35. Determine the unmodulated carrier 41. For a shorted coaxial transmission power of Problem 34. line with the following a. 15 kW characteristics: Zo = 75 Ω, Єr = 0.7, b. 10 kW f = 1.5 GHz, and Zin = -j70 Ω, c. 5 kW determine the length of the d. 50 kW transmission line. 36. Determine the audio power present a. 38 cm in the transmitted power of Problem b. 11.9 cm 34. c. 23.9 cm a. 10 kW d. 9.1 cm b. 15 kW 42. A 75-Ω transmission line is c. 5 kW terminated with a load equal to 25- d. 50 kW j50Ω, determine the reflection 37. Calculate the percentage power coefficient of the line. saving when the carrier and one of a. 0.362∠108.43 ° the sidebands is suppressed in an b. 0.132∠ 54° AM signal if the modulation index is c. 0.632∠ − 108.43 ° 25%. d. None of the above a. 83.3% 43. Determine the distance the quarter- b. 98.5% wave transformer must be placed c. 75% from the load to provide matching of d. 25% Problem 42. 38. A SSB transmission drives 110-Vpeak a. 0.0994λ into a 75-Ω antenna. Calculate the b. 0.3494λ PEP. c. 0.1234λ a. 161 W d. 0.2314λ b. 125 W c. 80.67 W d. 65 W Answer: C 39. What is the modulation index of an FM transmitter whose frequency