### EC6501  DC 2marks-16marks

Anna University Regulation 2013 Electronic Communications Engineering (ECE) EC6501  DC 2marks & 16marks for all 5 units are provided below. Download link for ECE 5th SEM EC6501  DIGITAL COMMUNICATION Short answers, Question Bank are listed down for students to make perfect utilization and score maximum marks with our study materials.

EC6501   DIGITAL COMMUNICATION QUESTION BANK

UNIT-I 2-marks

1. Define Dirac comb or ideal sampling function. What is its Fourier Transform? Dirac comb is nothing but a periodic impulse train in which the impulses are spaced by a time interval of Ts seconds.

2. Give the interpolation formula for the reconstruction of the original signal. The interpolation formula for the reconstruction of the original signal g(t) from the sequence of sample values {g(n/2W)}.

3. State sampling theorem. (Madras Univ., Nov-97,Oct-98,Dec-06,08,09,May-07,09,12) ¾

If a finite –energy signal g(t) contains no frequencies higher than W hertz ,it is completely determined by specifying its co=ordinates at a sequence of points spaced 1/2W seconds apart. ¾ If a finite energy signal g(t) contains no frequencies higher than W hertz, it may be completely recovered from its co=ordinates at a sequence of points spaced 1/2W seconds apart. ¾ A band limited signal of finite energy, which has no frequency components higher than W Hz, may be completely recovered from the knowledge of its samples taken at the rate of 2W samples per second.

4. Define quadrature sampling. Quadrature sampling is used for uniform sampling of band pass signals.

5. Define Nyquist rate. (Madras Univ, April-97) Let the signal be band limited to W Hz. Then Nyquist rate is given as, Nyquist rate = 2W samples/sec Aliasing will not take place if sampling rate is greater than Nyquist rate.

6. What is meant by aliasing effect? (Madras Univ,April-97,Dec-05) ¾ Aliasing effect takes place when sampling frequency is less than Nyquist rate. Under such condition, the spectrum of the sampled signal overlaps with itself. Hence higher frequencies take the form of lower frequencies. This interference of the frequency components is called as aliasing effect.

A band limited signal of finite energy, which has no frequency components higher than W Hz, may be completely recovered from the knowledge of its samples taken at the rate of 2W samples per second.

7. What is meant by PCM? Pulse code modulation (PCM) is a method of signal coding in which the message signal is sampled, the amplitude of each sample is rounded off to the nearest one of a finite set of discrete levels and encoded so that both time and amplitude are represented in discrete form.. This allows the message to be transmitted by means of a digital waveform.
8. What are the two fold effects of quantizing process?
1. The peak-to-peak range of input sample values subdivided into a finite set of decision levels or decision thresholds 2. The output is assigned a discrete value selected from a finite set of representation levels are reconstruction values that are aligned with the treads of the staircase.
2. The output is assigned a discrete value selected from a finite set of representation levels are reconstruction values that are aligned with the treads of the staircase.
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