The Effects of Multiple CW Interferers

When two or more CW transmitters create an electromagnetic field to which a susceptible device is exposed, the possibility that damage or performance degradation will result may, under certain circumstances, be increased by the effects of occasional phase coincidence among the transmitters. If they move into and out of phase fairly slowly, then, over finite tihe intervals of significant duration, the effective value of the combined voltage at a given point in the device can considerably exceed the long-term effective (rms) value. In this paper, an upper bound is placed on this short-term effective voltage for situations where the transmitted waveforms are sinusoidal and the susceptible device can be modeled as part of a linear circuit. It is shown that, if the separate contributions of the N transmitters have similar amplitudes and their frequencies are close together, the short-term effective value can occasionally exceed the rms value by 10 log, N dB or more for a significant time interval. In some cases, this difference might be enough to cause the device's threshold of damage or performance degradation to be exceeded.