EC6503 TLWG - Waveform Distortion
- 1. Academic Year 2017-18 EC5603 Transmission Lines and Waveguides Waveform Distortion Mrs.R.Chitra, AP/ECE, Ramco Institute of Technology, Rajapalayam
- 2. WHAT IS DISTORTION? When the received signal is not the exact replica of the transmitted signal, then signal is said to be distorted. For ideal transmission, waveform at the = waveform of the original line-receiving end input signal The condition requires that all frequencies must have 1. Same attenuation 2. Same delay When these conditions are not satisfied, distortion exists.
- 3. TYPES OF DISTORTION The distortions occurring in the transmission line are called waveform distortion or line distortion. Waveform distortion is of two types: 1. Frequency distortion 2. Phase or Delay Distortion.
- 4. SOURCES OF ATTENUATION AND DISTORTION
- 5. FREQUENCY DISTORTION In general, the attenuation function(α) is a function of frequency. Attenuation function specifies the attenuation or loss incurred in the line while the signal is propagating. When a signal having many frequency components are transmitted along the line, each frequency is having different attenuation. This type of distortion is called frequency distortion. In this distortion, various frequency of the signal undergo different attenuations. When the attenuation constant is not a function of frequency, frequency distortion does not exist on transmission lines. Frequency distortion is important aspect for audio signal.
- 6. WAY TO REDUCE FREQUENCY DISTORTION In order to reduce frequency distortion occurring in the line, 1.The attenuation constant (α) should be made independent of frequency. 2. By using equalizers at the line terminals which minimize the frequency distortion. Equalizers are networks whose frequency and phase characteristics are adjusted to be inverse to those of the lines, which result in a uniform frequency response over the desired frequency band, and hence the attenuation is equal for all the frequencies.
- 7. DELAY DISTORTION When a signal having many frequency components, those frequencies will not have same time of transmission. Some frequencies being delayed more than others. This type of distortion is called phase or delay distortion. When the velocity is independent of frequency, delay distortion does not exist on the lines. It is independent of frequency when β is equal to a constant multiplied by ω. The phase distortion is not important for the audio signal due to the characteristics of the human ear. It is serious for videos and picture transmission.
- 8. WAY TO REDUCE DELAY DISTORTION In order to reduce delay distortion occurring in the line, 1.The phase constant should be made dependent of frequency. 2. The velocity of propagation is independent of frequency. 3. By using Coaxial cables
- 9. DISTORTIONLESS LINE: A line, which has neither frequency distortion nor phase distortion is called a distortion less line. Distortionless condition can help in designing new lines or modifying old ones to minimize distortion.
- 10. CONDITION FOR A DISTORTION LESS LINE The condition for a distortion less line is RC=LG. Also, 1. The attenuation constant (α) should be made independent of frequency. α= (𝑅𝐺)1/2 2. The phase constant (β) should be made dependent of frequency. β = ω (𝐿𝐶)1/2 3. The velocity of propagation is independent of frequency. ν=1 / (𝐿𝐶)1/2
- 11. CONCLUSION Transmission line will have neither delay nor frequency distortion only if 1. α is independent of frequency 2. β should be a function of frequency.
- 12. REFERENCES: John D Ryder, “Networks, lines and fields”, 2nd Edition, Prentice Hall India, 2010. E.C.Jordan and K.G. Balmain, “Electromagnetic Waves and Radiating Systems”,Prentice Hall of India, 2006. G.S.N Raju "Electromagnetic Field Theory and Transmission Lines”, Pearson Education, First edition 2005.