Thermal noise

This is sometimes called Browian or Gaussian noise and is noise that is associated with the random movement of electrons at tem­peratures above absolute zero.

For the FDM range of frequencies the noise power that is gener­ated is given by Equation 20.3, where P is noise power in watts, k is Boltzmann's constant, T is the absolute temperature in degrees Kelvin, and B is bandwidth in Hz.

If T = 310°K and B = 4000Hz then the available noise power is -137.5dBm.

The absolute thermal noise power at the output of a circuit element of gain GdB and noise figure FdB within a 4kHz channel is given by Equation 20.4.

If the absolute power at the transmission level point T is known (TL in dBm) then the thermal noise contribution to the noise power in a 4kHz channel can be calculated in dBmOp (or pWattOp) as in expressions 20.5 and 20.6, where 3.6dB is the weighting factor for a 4kHz bandwidth. Definitions of the noise factor F are found in Connor, 1973.