CISPR Quasi-Peak Measuring Channels with Extended Dynamic Range

Abstract

The paper deals with instruments for radio-noise measurements according to the CISPR recommendations; however, the ideas described can be applied also in non-CISPR-type meters. A limited instantaneous dynamic measurement range is a common drawback of the classic CISPR (and non-CISPR) meters currently used. One of the most important factors limiting this range is a nonlinearity of the measuring channel. The paper describes two new methods of improving the channel linearity and extending its dynamic measurement range. The first of them is based on application of a precision quasi-peak detector, whereas the second method is founded on splitting the measured signal into several separate subehannels, and synthesing the resulting output. A simplified theory is outlined, and experimental results are presented. The precision quasi-peak detector application results in a linear input-output relation, whereas the signal-splitting/synthesizing technique makes this relation logarithmic. An increase of dynamic range by 20 to 40 dB has been demonstrated practically in experimental models built.