7.1 Noise Fundamentals

Any object capable of allowing the flow of any electric current will generate noise. The noise is generated by random vibrations of electrons in the material. The vibrations, and hence the noise power, are proportional to the physical temperature in the material. This noise is referred to as ‘thermal noise’.

7.1.1 Thermal Noise

Thermal noise is ‘white noise’; white noise has its power distributed equally throughout the total RF spectrum, from the lowest frequency all the way to the highest microwave frequency.

Spectral Noise Density

In other words, the power spectral density of white noise is constant over the RF frequency spectrum; hence the noise power is proportional to the bandwidth. If the bandwidth of the RF channel is doubled, the thermal noise power will also double (+3 dB).

Thermal Noise Level

In order to be able to calculate the noise power of a given bandwidth, you need to establish the ‘base noise’, that is, the noise in 1 Hz bandwidth. Knowing this level, you can simply multiply the noise power in 1Hz by the bandwidth in Hz. Thermal noise power is defined as

Where P is the noise power at the output of the thermal noise source (dB W), K is Boltzmann's constant , T is temperature (K) and B is the bandwidth (Hz).

Reference Noise Level per 1 Hz

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