TABLE OF CONTENTS Signals measured during radiated and conducted emission tests are often extremely complex, consisting of a mixture of individual signals from many separate sources within the equipment. Some of these may emanate from stable oscillators for example, producing a sinusoidal waveform at a single frequency. The frequency extent or bandwidth of this signal is small, perhaps less than 1 Hz, and it is clearly narrowband.
Other circuits which generate fast switching waveforms such as switched mode power supplies or digital processing circuits produce signals which contain many frequency components which may be spread across tens or hundreds of megahertz. These signals have a wide bandwidth with the highest frequency being determined by the switchinG-edge risetime/falltime, and the spacing of frequency components in the spectrum by the switching repetition frequency. Such a signal is referred to as broadband.
Measuring the amplitude of a narrowband signal with a tuned radio receiver or EMI meter is simple, as once the receiver is tuned to the signal frequency at say f 1 MHz, the measured signal strength is independent of the bandwidth used to measure it. This is because all the power in the signal is always contained within the 3 dB passband of even the narrowest IF (intermediate frequency) and post-detector filters as shown in Figure A1.1 a.
This is not the case with broadband noise or impulsive signals where the power in the signal is distributed over...
