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Harmonics in Clocks Creating EMI Problems

Clock signals from 1 to 100MHz are usually responsible for radiated EMC problems in HF/VHF range. Harmonics are the culprits, but think in current, not in voltage.
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Harmonic Measurement for IEC 61000-4-3 and other Radiated Immunity Standards

In the rush to complete RF immunity testing on schedule, it is not all that unusual to overlook inherent test equipment limitations. While some test equipment characteristics such as power amplifier harmonics are obviously a limiting factor, the broadband characteristics of antennas, directional couplers, power meters and isotropic field probes can hardly be considered a limitation for most applications. However, when used with power amplifiers exhibiting significant harmonic distortion in Immunity test systems, the broadband characteristics of these devices can result in measurement uncertainty and unacceptable errors.