Distributed Noise Emission Spectra

The amplitude of an emission spectrum which is generated by a noise modulated transmitter is properly calibrated in the power spectral density terms of power per bandwidth or watts/kHz. When a photograph is taken of the measured spectrum, it sometimes becomes difficult to determine the power spectral density at a particular point of the distributed spectrum. The relative scale is easily obtainable in dB but the absolute value is seldom if ever given correctly on measured data. The purpose of this paper is to develop a method for determining the largest absolute value of power spectral density for four most used transmission modes in communications; namely, single sideband, amplitude modulation, narrowband and wideband frequency modulation. A single equation is developed which expresses the maximum power spectral density as a function of average power, bandwidth and modulation factor. These three quantities are easily obtainable from manufacturers' information or measured data.