Transmission Media -Cont

Transmission Impairments Transmission media are not perfect What is sent is not what is received

Attenuation o    Attenuation means loss of energy o    Some of electrical energy is converted to heat    Decibel (dB) Relative strengths of two signals or a signal at two points dB = 10 log  10 (P  2/P  1) P  2 and P  1 are signal powers Negative dB means attenuation Positive dB means amplification Example 7.1 Imagine a signal travels through a transmission medium and its power is reduced to half. This means P  2=(1/2)P  1. Calculate Attenuation? Solution: -10log  10(P  2/ P  1)= 10log  10(0.5 P  1/ P  1) =10(-0.3)= -3 dB    Distortion o    Distortion means that the signal changes its form or shape o    Distortion occurs in a composite signal