DATA COMMUNICATION THEORY
Report on Digital Transmission of Analogue Signals
Pulse Amplitude Modulation
The experiment uses the L.J.Electronics Modicom-1 board to investigate the sampling of signals, and the filter effects on the reconstruction of the original signal from the sampled input. The sample/Hold operation is also investigated in this experiment.
The Modicum -1 board allows an analogue signal to be sampled at a number of different rate(2kHz,4kHZ,8kHZ,16kHz,32kHz).The pulse width is varied in the steps of 0% from 0 to 90 of the sampling interval. Second order and fourth ...view middle of the document...
4 KHz and a pass band gain of 1.56. The input of the filter is attenuated by resistor chain R34 & R35 and its value is chosen in such a way to give the overall SECOND ORDER LOW PASS FILTER block a gain of unity. The final filter output appears at the terminal point TP (44).
Fourth Order Low Pass Filter:
It has a break frequency of 3.4 kHz and a pass band gain of 2.55.The input of the filter is attenuated by resistor chain R24 & R 25 and its value is chosen in such a way to give the overall FOURTH ORDER LOW PASS FILTER block a pass band gain of unity. The final filter output appears at the terminal point TP (49).
Frequency selector Push Button:
It is used to select the frequency of the internal sampling control signal. Each time the push button is pressed, a different LED is illuminated in the sampling control logic block. The LED’s are labeled as 320kHZ,160kHZ,80kHz ,40kHz and 20kHz and the frequency is divided by 10 so the resulting sampling frequencies are given by 32kHz,16kHz,8kHz,4kHz and 2KHz.
Duty Cycle Selector Switch:
It is a ten position switch which allows the duty cycle of the sampling control signal to be varied in discrete steps of 0% to 90%.0% duty cycle indicates that there is no sampling and 90% indicates that analog signal is sampled 90% of the time.
Sampling Control Switch:
The sampling control switch allows a sampling control signal to be provided by an external source through the SAMPLING CONTROL UNIT. The sampling control switch must be in an external position in order to use an external sampling control signal. If on-board sampling control signal is going to be used then the sampling control switch must be in internal position.
(commonly abbreviated to scope or O-scope) is a type of electronic test equipment that allows signal voltages to be viewed, usually as a two-dimensional graph of one or more electrical potential differences (vertical axis) plotted as a function of time or of some other voltage (horizontal axis). The oscilloscope is one of the most versatile and widely used electronic instruments. Oscilloscopes are widely used when it is desired to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can measure the frequency, show distortion, and show the relative timing of two related signals. Oscilloscopes are used in the sciences, medicine, engineering, telecommunications, and industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for such purposes as adjusting an automotive ignition system, or to display the waveform of the heartbeat.
To investigate the principals of sampling to give Pulse Amplitude Modulation (P.A.M) and its characteristics.
Equipments used in this Experiment are as follows: