1. Prepared by Engr.Jawad Ali University of Engineering and technology peshawar pakistan

2. Transmission impairment  Signal travel through medium which is not perfect, the imperfection cause signal impairment, what is sent is not what is received.

3. Causes of impairment

4. Attenuation  Attenuation means a loss of energy.  When a signal travels through a medium it loses some of its energy in overcoming the resistance, which heats up the wire.  To compensate for this loss amplifiers are used to amplify the signal.

5. Attenuation (cont)

6. Decibel  To show the strength of the signal engineers use the limit of the decibel(dB).  The decibel measure the relative strength of two signals or one signal at two different points.  Decibel is negative if signal is attenuated and positive if it is amplified.

7.  dB=10log 10 (p2/p1)  dB=20log 10 (v2/v1)

8. Example 1  Suppose a signal travel through a transmission medium and its power is reduced to one half, find the attenuation or power loss.

9. Solution  As power is reduced to one half it means that p2=1/2p1.  The loss of 3dB(-3dB) is equivalent to losing one half of the power.

10. Example2(home work)  A signal travel through an amplifier and its power is increased 10 times, find the amplification or gain of power.

11. Distortion  Distortion means that the signal change its shape or form.  Signal components at the receiver have phases different from what they had at the sender.

12. Distortion (cont)

13. Noise  Several Types of noise are  Thermal noise  Crosstalk  Impulse noise  Induced noise

14. Signal to noise ratio(SNR)  High value of SNR means signal is less corrupted by the noise and low value of SNR means signal is highly corrupted by the noise.

15. SNR (Cont)  Because SNR is the ratio of two powers it is often described in decibel units  SNR dB = 10 log 10 SNR

16. Example  The power of signal is 10 mW and the power of noise is 1 µW what are the values of SNR and SNR dB.

17. Solution

18. Throughput  Throughput is the measurement of how fast data can pass through an entity (such as a point or a wall).

19. Propagation time  Propagation time measures the time required for a signal (or a bit) to travel from one point of transmission medium to another.  The propagation time is calculated by dividing the distance by the propagation speed.