# Noise factor for a system is defined as the ratio of

**Q9. Noise factor for a system is defined as the ratio of**

**Options: **

a) Input noise power (P_{no}) to output noise power (P_{ni})

b) output noise power (P_{no}) to input noise power (P_{ni})

c) output noise power (P_{no}) to input signal power (P_{si})

d) output signal power (P_{so}) to input noise power (P_{ni})

Correct Answer: b) output noise power (P_{no}) to input noise power (P_{ni})

**Explanation :**

The noise factor of a system is defined as the ratio of output noise power (P_{no}) to input noise power (P_{ni}):

F_{n} = P_{no}/ P_{ni}, at standard room temperature 290K

= P_{no}/GKBT_{0}

The input noise power is P_{ni}= GKBT_{0},

G is the gain of the amplifier

K= 1.38 X 10^{-23} J/°K , Boltzmann's constant

B is the bandwidth of the network in hertz (Hz)

To = 290°K

Noise factor may also be defined as the ratio of Signal to Noise ratio at the output to Signal to Noise ratio at the input.

i.e., F_{n} = S_{ni}/ S_{no}