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Home Electrical and Electronics Digital Communication Identify the various Line Coding Schemes for a given data stream
Digital Communication Lab Experiments

Identify the various Line Coding Schemes for a given data stream



Objective:

Identify the various Line Coding Schemes for a given data stream.

Apparatus Required:

  1. Data Formatting kit
  2. Cathode Ray Oscilloscope (CRO)
  3. Binary Data Generator
  4. Power supply
  5. Patch cords

Theory

'1' and '0' can be represented in various formats in different levels and waveforms. The selection of coding technique depends on system band width, system’s ability to pass dc level information, error checking facility. Non return to Zero (level): The NRZ(L) waveform simply goes low for one bit time to represent a data ‘0’ and high to represent data ‘1’.For lengthy data the clock is lost in asynchronous mode. The maximum rate at which NRZ can change is half the data clock when alternate 0’s and 1’s are there. In Manchester Biphase ‘0’ is encoded low during first half of bit time & high for other half of bit & vice versa for ‘1’.There is no synchronization problem in the receiver. It is independent of DC levels, since there is a transition occurring in each bit. Its maximum frequency is equal to data clock rate. There is at least one transition per bit. Since there is midway transition, it makes clock regeneration difficult so we use special bi phase clock recovery circuit

various-line-coding-schemes

Procedure:-

  1. Make the circuit as shown in figure 2.2.
  2. Connect the power supply in proper polarity to the kit and & switch it on.
  3. Set the pulse generator output to be 2Vpp at 8 Khz.
  4. Observe waveform at output for various encoding scheme and trace on graph paper.
  5. data-formatting-kit

Observation:Figure 2.3 is the data clock. The different output waveforms shown in figures 2.4 (a) to (d) are observed with the help of CRO and are traced with the help of graph paper.

data-clock
(a)-(b)
(a)-(b)
various-coding-scheme-(a)nrz(b)rz(c)bi-phase(d)differentially-encoded

Conclusion:The study of various encoding scheme has been successfully done.

Questions:

  1. What is the use of data formatting?
  2. Compare NRZ and biphase encoding.
  3. What is the relationship between quantization levels and number of bits in a code word?
  4. Give the advantages of Manchester encoding.

Precautions:

  1. Check the connections before giving the supply.
  2. Observations should be done carefully