Question 20.12: The diagrams in Figure 20.12 show a digital signal at the st...
The diagrams in Figure 20.12 show a digital signal at the start of a long cable and at the end of the cable. Both diagrams are drawn to the same horizontal scale (time) and vertical scale (voltage).
a Explain what feature of the top diagram shows that the signal is digital.
b State and explain two advantages of digital transmission over analogue transmission of data.
c State and explain two reasons why the signal at the end of the long cable differs from the signal at the start.
a The value on the vertical axis (the voltage) has only one of two values, 0 or 1.
b Digital signals can be more easily regenerated, can be stored and processed more easily, errors in transmission can be detected and digital electronic systems are more reliable.
c Noise is introduced, e.g. by random thermal motion of electrons. The signal is attenuated due to energy loss (I²Rt) in the wires