Subject : Principle of Communication Engineering

Topic : Introduction to Electronic Communication

Difficulty : Low

1) Signal-to-noise ratio (SNR)

• Signal to noise ratio is defined as the ratio of the signal power to the noise power at the same or equivalent point in the system.
• It is a measure of signal strength relative to the background noise.
• It is often denoted as SNR and expressed in decibels.

• Signal to noise ratio is given as

  SNR = Ps/Pn (unit: W)

Where,

Ps = signal power,

Pn= noise power.

SNR in dB is given as:

SNR in dB = 10 log⁡(Ps/Pn) (unit: dBW)

Noise factor

Noise factor is defined as the ratio of the SNR at the input to the SNR at the output. It is given as:

F = (SNR at input)/(SNR at output) =Psi/Pni×Pno/Pso

Noise factor is always greater than one, and has unity as the ideal value.

b) Noise temperature

Equivalent noise temperature is defined as the absolute temperature at which a perfect resistor, of equal resistance to the component, would generate the same noise as the component at room temperature.

Equivalent noise temperature given in terms of noise figure as:

Te = T0(F-1)

Where T0= 290K

c) Noise figure

Noise factor expressed in decibels is called as Noise figure.

Noise figure is given as:

Noise figure = F dB = 10 log F

= 10 log⁡(SNR at input) - log⁡(SNR at output)

The ideal value of noise figure is 0 dB.