CISPR Publications 24 and 35 allow radiated and conducted immunity tests to be performed using I% or 4% steps. This article looks at measured radiated immunity test data to determine the typical shapes of radiated susceptibilities for multimedia equipment. The authors consider what those shapes tell us about the validity of the 4% step method.
The pressure to bring new products to the market, with reduced time to market, high quality and reduced cost, has never been greater.
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.