IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. EMC-20, NO. 3, AUGUST 1978 CISPR Quasi-Peak Measuring Channels with Extended Dynamic Range RYSZARD G. STRUZAK Abstract-The paper deals with instruments for radio-noise measure- ments 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. Key Words: Radio-noise meter, extended dynamic range, quasi- peak, CISPR. INTRODUCTION MEASUREMENTS are of fundamental importance in the area of electromagnetic compatibility, and great efforts are being made to improve EMC measuring techniques. Among several international organizations concerned, the CISPR1 reached the most significant results in this field. The CISPR measuring channel has been accepted officially as a legal refer- ence in radio-interference measurements by the majority of countries and international organizations interested [2]-[5]. However, although the CISPR recommendations combine the best worldwide experience from the not so distant past, the CISPR-type meters currently used are not very suitable for some specific applications. For example, recording of signals showing great magnitude variations is not possible with such an apparatus without intervention from an operator. This inconvenience results mainly from the limited instantaneous dynamic measuring range of the CISPR channel. To avoid this inconvenience, an automatic gain control (AGC) is sometimes used [6]. However, this solution leads to Manuscript received July 13, 1977; revised December 30, 1977. This is a revised version of the paper [1] which was presented at the International Symposium on Electromagnetic Compatibility, Montreux, Switzerland, June 28-30, 1977, and won the prize award there. The author is the head of the Institute of Telecommunications, Wroclaw Branch. He is also with the Technical University of Wroclaw, Wroclaw, Poland. Telex 0712 118ilpl. 1 International Special Committee on Radio Interference. results which may be entirely noncomparable with indications of the reference CISPR measuring channel. The purpose of this paper is to present new methods of improving the linearity of CISPR-type measuring channels and extending their dynamic range without AGC introduction.2 The ideas described might be applied also in non-CISPR-type meters. CLASSIC CISPR-TYPE MEASURING CHANNEL The CISPR reference channel is realized as a linear-measur- ing radio receiver, usually of the superheterodyne type, with only the manual control of sensivity, and analog-type out- put [2] - [5]. Without loss of generality, it can be represented as in Fig. 1. In this figure, local oscillators, attenuators, and other elements are omitted because they do not introduce any essential contribution into our considerations. Fig. 1 represents a broad class of radio-noise measuring instruments of different types. The CISPR reference channel differs from others by numerical values of parameters describ- ing explicitly the functional blocks shown in Fig. 1. For example, according to the CISPR specification for the fre- quency range 0.15 MHz to 30 MHz [2], the nominal band- width of the filter in Fig. 1 is 9 kHz. The electrical time- constants of the quasi-peak detector are 1 ms (charge) and 160 ms (discharge), and the mechanical time constant of the indicating instrument (critically damped) is 160 ms. The linearity of channel elements is specified in terms of overload factor. This factor shows how large a signal can be processed without noticeable nonlinear distortion. The overload factor of the HF amplifier (generally, circuits preceding the detector) is 30 dB above the level of the sinewave signal which produces the maximum deflection of the indicating instrument. The overload factor of the dc amplifier (generally, circuits between the detector and the output) is 12 dB above the dc voltage level corresponding to full-scale deflection of the indicating instrument. The linearity requirements mentioned above for the quasi-peak detector are set to accommodate the pulse response of the channel to well-defined standard pulse and pulse trains. Close tolerances are prescribed for each of these reference-channel parameters in order to ensure the repeat- ability of measurements made by different observers, at 2 The dynamic measurement range of the channel is the range spreading from the minimum to the maximum mark on the scale of the indicating instrument (without gain adjustment). 0018-9375/78/0800-0361$00.75 © 1978 IEEE 361