Types
Depending on the intended application area, several types of measuring receivers can be distinguished:
- Spectrum analyzers are intended to graphically display the amplitude spectrum of a radio signal on a logarithmic scale.
- Modulation analyzers are intended to accurately measure not only the signal power level, but also the degree of modulation (such as AM depth, FM/PM deviations), and modulation distortions.
- EMI receivers are designed to comply with the detailed equipment requirements of measurement standards for radio interference, such as the civilian specification CISPR 16-1-1 or the military specification MIL-STD 461. The EMI receiver has defined IF-Bandwidths (typically 200 Hz, 9 kHz, 120 kHz, 1 MHz) and standardized detector modes (peak, quasipeak, average, rms, CISPR-AV and CISPR-RMS, RMS-Average). They use a preselection for an improved dynamic range. Rohde & Schwarz holds the German Patent DE10126830B4 for RMS-Average Detector, which describes a implementation that allows to fulfill CISPR 16-1-1.
- Time-domain EMI Measurement systems are systems that perform a baseband sampling and simulate all the IF-Bandwidths and detectors digitally. Typically this is done via Short Time Fast Fourier Transform (STFFT). Such measurement systems emulate several thousand EMI receivers digitally in parallel. The most advanced instruments allow to speed up the measurement by a factor of 4000. Measurements can be performed according to the standards CISPR 16-1-1, MIL-STD 461 and DO-160. The benefit are extremely fast full compliance measurements. The measurements are performed with defined IF Bandwidths according to CISPR or MIL-STD 461F as well as DO160 and the detector modes (peak, quasipeak, average, rms, CISPR-AV and CISPR-RMS, RMS-Average). They use a preselection for an improved dynamic range.
- TEMPEST receivers are designed to comply with the requirements of measurement standards for compromising-emanations such as SDIP-27 or NSTISSAM TEMPEST/1-92. For example, their frequency range extends down to acoustic frequencies (typically 100 Hz), their bandwidth can be adjusted in 1-2-5 steps from a few hertz to more than 100 MHz, and their sensitivity and noise figure aims to be close to what is technically feasible.
Some measuring receivers (such as Agilent’s N5531S and MXE or Rohde & Schwarz's FSMR and ESU) also include a signal analyzer, power meter, and a sensor module to allow the instruments to be used together or individually for general-purpose measurement tasks.
The time-domain EMI measurement systems TDEMI of Gauss Instruments show additional features like weighted spectrogram mode, oscilloscope mode as well as measurement of discontinuous disturbance according to CISPR 14-1.
Read more about this topic: Measuring Receiver
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