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TELECOMMUNICATIONS 1 (INEL 4301) Name: _____________________________ Section: 010 020 Final Exam Autumn 2005 Expect to receive full credit only for answers that are thoroughly substantiated. 1. (40) Assume an FM modulator with f d 8 Hz/V, a carrier 10 cos(1000t ) and the message given by 10 cos( 20t ) . The modulated FM signal is passed through an ideal band pass filter with center frequency 500 Hz, bandwidth 70 Hz. a.) What is the peak frequency deviation? b.) What is the phase deviation? c.) What is the modulation index? d.) What are the powers at the input and at the filter output? e.) Draw to scale the single-sided spectrum of the signal at the filter output. Label the amplitude and frequency axes. 2. (40) The signal 3 sin( 8000t ) is quantized and transmitted using a PCM system. If each data sample at the receiving site must be know within 0.10 of the peak value, a.) How many binary symbols must each coded word contain? Make sure to choose a practical value. b.) What is the bandwidth of the resulting PCM signal? c.) Discuss the types of noise present in the receiving system Noise from Quantization: One of the types of error introduced into an analog audio signal by encoding it in digital form. The digital equivalent of tape hiss, quantization noise is caused by the small differences between the actual amplitudes of the points being sampled and the bit resolution of the analog-to-digital converter. Noise from the Channel (word error): This error is caused by the additive probability of having an error in each bit.(p. 318-319) d.) Can the S/N ratio always be improved by simply increasing the signal (message) level? Why? If “signal (message) level” is related to the value of PT (ask the professor), then the following applies: Ver parrafo que dice “If the additive noise in the channel……”. 3. (20) Answer the following questions. a.) How many ways are there to improve SNR in an FM system? Discuss. (Hint: Table 6.1). Sec. 6.3.4 Improve output SNR Example 6.3 Preemphasis and deemphasis can be used to partially combat the effects of interference. These techniques can also be used to great advantage when noise is present in angle modulation systems Summary Chap 6 #10 b.) Describe briefly the threshold effect in the case of interference in linear modulation. Discuss separately the cases of coherent and envelope detections. Summary Chap 6 #4 -> coherent and envelope demodulation. 148-150