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# EC8394 Important Questions Analog and Digital Communication

EC8394 Important Questions Analog and Digital Communication Regulation 2017 Anna University free download. Analog and Digital Communication Important Questions EC8394 pdf free download.

## Sample EC8394 Important Questions Analog and Digital Communication:

1. Define noise and noise figure.
Noise is defined as any unwanted form of energy, which tends to interfere with proper reception and
reproduction of wanted signal.
Noise figure is defined as the ratio between Signal to Noise ratio at the output to the Signal to Noise
ratio at the input
2. What are the types of external noise and internal noise? EC8394 Important Questions Analog and Digital Communication
External noise can be classified into Atmospheric noise, Extraterrestrial noises,Man –made noises or
industrial noises.Internal noise can be classified into Thermal noise, Shot noise, Transit time noise,
Miscellaneous internal noise.
3. What are the types of extraterrestrial noise and write their origin.
The two type of extraterrestrial noise are solar noise and cosmic noise Solar noise is the electrical
noise emanating from the sun. Cosmic noise is the noise received from the center part of our galaxy,
other distant galaxies and other virtual point sources.
4. Explain thermal noise. EC8394 Important Questions Analog and Digital Communication
Thermal noise is the name given to the electrical noise arising from the random motion of electrons in
a conductor.
5. Give the expression for noise voltage in a resistor.
The mean square value of thermal noise voltage is given by Vn2 = 4 K T B R where K – Boltz man
constant, R – resistance, T – Absolute temperature, B – Bandwidth
6. Explain White Noise. EC8394 Important Questions Analog and Digital Communication
Many types of noise sources are Gaussian and have flat spectral density over a wide frequency range.
Such spectrum has all frequency components in equal portion, and is therefore called white noise. The
power spectral density of white noise is independent of the operating frequency.
7. What is the need for modulation?
It is extremely difficult to radiate low frequency signals through earth’s atmosphere in the form of
electromagnetic energy.
At low frequency, the antenna size required becomes impractical.
Information signals often occupy the same frequency band. Signals from two or more sources would EC8394 Important Questions Analog and Digital Communication
interfere if they are not modulated and translated to a different frequency band.

 Subject name Analog and Digital Communication Semester 3 Subject Code EC8394 Regulation 2017 regulation