y the frequency components and their corresponding amplitudes. The amplitude of signal components in a time or frequency domain can be used to calculate the overall signal power. For example, signal power is calculated by averaging the square of signal amplitude over time: that is if A is the instantaneous amplitude, power is equal to the average of A2 over time. For waveforms of interest in telecommunications, power in most cases is equal to the average of A2/2. Signal power is measured in watts, in honour of James Watt (1736-1819) the inventor of the steam engine. It is an important measure Information Theory in evaluating the quality of signal in the presence of noise: a high ratio of signal power to noise power (signal to noise ratio, SNR) indicates a clear, high quality signal, and a low SNR indi- cates a poor signal, which may not be intelligible. Both signal and noise power are measured similarly and with the same unit of watts. Thermal Noise Thermal noise is a natural process and is produced in any physical device that exists in above absolute-zero temperatures, that is 0 K or -273 °C. The power of thermal noise N in watts is calculated from the following formula: N kgTB where kB is the Boltzmann constant and equal to 1.38x10-23 J/K, T is the absolute temper- ature in kelvin and B is the signal bandwidth in hertz. For example, a voice signal trans- mitted at room temperatures (27 °C or 300 K), will be received with an additive noise signal of a power N=1.38x10-23x300x4000=1.66x10-17 W or - -137.8 dBm. Signal and noise power are calculated at a telecommunications receiver. Noise power is generally produced locally and is a product of molecular friction in the receiving device. Received signal power is a function of the transmitted power, transmitting and receiving device characteristics, antennas, and the signal loss in the communications medium. Calculations are done using a technique known as Link Budget. These calculations are usually done using the decibel (dB) scale, a logarithmic operation which make