Industrial Equipment Spectrum Signatures

This paper presents a survey of the radiation characteristics (spectrum signatures) of electrical and electronic equipment such as rectifiers, welders, power lines, switching devices, ignition systems, induction heaters, and electric motors. Several equipment signatures were compiled from reports on interference. The reports indicated that some industrial activities radiate strongly enough to cause interference at ranges up to a few miles and that most of the energy is concentrated in the low-frequency portion of the spectrum. The equipment was measured at very low frequencies at the Douglas Aircraft Company, Santa Monica, Calif., using Stoddart Aircraft Radio Company receivers. Graphs of the measurements show strong and unique signatures in the SLF and ULF (30 - 3000 cps) bands.