<p> ECE 342 Midterm</p><p>Name:______A. Multiple Choices (30 points, 3 points each)</p><p>1. What is the feature of analog communications? ( ) A. Transmission in continuous time and continuous value. B. Analog devices are used in both transmitter and receiver. C. The signal is transmitted through a continuous time channel. D. Noisy communication channels.</p><p>2. Which of the following is NOT a feature of thermal noise incurred by motions of free electrons in conductor? ( ) A. Flat frequency spectrum in a very wide band. B. The noise is almost independent in the time. C. The noise power is proportional to the temperature. D. It has many abrupt impulses.</p><p>3. Which of the following is a distortion for the signal transmission? ( ) A. Delay B. Scaling of amplitude C. Passing through a linear system with frequency selective response D. Demodulation</p><p>4. In a free space transmission of wireless signal, which of the following is correct for the received power (d is the transmission distance)? ( ) 2 A. Pr µ1/ d 3 B. Pr µ1/ d 4 C. Pr µ1/ d 5 D. Pr µ1/ d</p><p>5. Which of the following is correct for DSB? ( ) A. There is a carrier component. B. There is not carrier component. C. The modulation index is 1. D. The modulation index is -1.</p><p>6. Which of the following picture is D. Middletown? ( )</p><p>A. B. C. D. </p><p>7. Which of the following AM schemes may not need a coherent demodulation? ( ) A. DSB B. VSB C. SSB D. AM with a small modulation index</p><p>8. What is a benefit of carrier component in AM? ( ) A. Provide carrier for the receiver B. Save power C. Save bandwidth D. Save device</p><p>9. Which of the following angle modulation is similar to AM? ( ) A. FM of a tone B. PM of a tone C. Narrowband PM D. Wideband FM</p><p>10. Which of the following determines the gap between spectrum lines in a single tone FM? ( ) A. Carrier frequency B. Frequency of the modulating signal C. Modulation index D. Amplitude of modulating signal</p><p>B. Signal and Noise (30 points)</p><p>Consider signal being transmitted in a free space. The transmitted power is 2W and the transmission distance is 1000 meters. It has been measured that the received power at the distance of 100 meters is -95dBW. The temperature at the receiver is 300K and the resistance is 1Om. Then, what is the value of SNR at the receiver? (the Boltzman constant -23 kB =1.3806488´10 ) C. Amplitude Modulation (20 points)</p><p>(1) Explain what DSB, SSB and VSB are. (2) Signal x(t) = cos2p100t + 4cos2p 200t is transmitted using DSB with carrier frequency 5000Hz. Sketch the positive-frequency line spectrum. Repeat it when SSB is used. D. Angle Modulation (20 points)</p><p>Consider a single tone modulated FM wave with fm = 20kHz, b = 3, Ac =10</p><p> and fc = 200kHz . Write the expression for the modulated signal. Sketch the line spectrum. Repeat your solution if the modulating signal is x(t) = cos2p 5000t + 2cos2p10000t. average = 70.6, standard deviation = 16.7</p>