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.