Subject : Principle of Communication Engineering

Topic : Introduction to Electronic Communication

Difficulty : Medium

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

Where,

PS = signal power,

PN= noise power.

SNR in dB is given as:

SNR in dB = 10 log⁡(PS/PN )

1. Noise Power

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.

1. 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.

4. Equivalent 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