Ultra-fast real-time spectrum analysis for investigation of communication signals

Measurements of electromagnetic interference in time-domain allow to reduce the scan time by several orders of magnitude, in comparison to automated scans performed by the tuned selective voltmeters, which are known as EMI receivers. Spectrum analyzer are used for fast sweeps to get an overview. Such analyzers can perform fast sweeps or scans over large bands. With the update of CISPR 16-1-1 Ed 3.1 the requirements for time-domain EMI measurement systems have been described. These time-domain EMI measurement systems are using the short-time fast Fourier transform to simulate a set of up to 4000 receivers simultaneously. A major requirement is the gapless aquisition during the dwell time. In this paper the requirements and solutions for time-domain measurements are discussed. A major requirement is the gapless processing of the input signal. In this paper implementation and application of short-term FFT based spectrum analysis for the use of measurements of communication signals is discussed. The short-term FFT represents a set of superheterodyn receivers. The output signal is extracted at each processed frequency. At each frequency the emulation of the analog video filter as well as of the detectors is performed. By the parallel implementation the sweeptime is reduced by at least three orders of magnitude. Further the observation time is increased allowing to perform fast and precise measurements of fluctuating signals. Examples on measurements of typical communication signals are presented.