Spectrum Analyzers and EMI Receivers are very common in LED Lighting, home appliances, communications and power tools testing, and many tests can be completed independently. So what are the differences between them?
1. Principle differences:
Spectrum Analyzer: The main tool for spectrum analysis, sweep out-of-band is the mainstream, using sweep measurement technology, obtaining external difference signal for frequency-domain dynamic analysis through sweeping signal source.
EMI Receiver: The main tool for EMC test, based on point frequency modulation, using self-excited tuning principle to test the level value of the corresponding frequency point, the scanning mode of the EMI receiver is step-frequency tuning.
2. Different front-end processing of input RF signals:
Spectrum Analyzer: The signal input end usually has a set of simple low pass filters.
EMI Receiver: A strong anti-interference pre-selector must be adopted for wideband signals, usually including a set of fixed bandpass filters and a set of tracking filters to complete the preselection of the signal. The EMI receiver requires higher accuracy and requires an additional pre-selector in front of the ordinary spectrum analyzer.
3. Different scanning signals:
The sweeping signal source of the spectrum analyzer is usually controlled by a sawtooth or sawtooth signal to achieve, the frequency change is continuous, and the desired mixing output signal is obtained by scanning in the preset frequency span.
The frequency signal scanning of EMI receivers is discrete point frequency scanning. According to the frequency interval preset by the operator, the level measurement is carried out at each frequency point through the control of the processor, and the test results curve displayed is actually the results of single point frequency test. Now EMC measurement requires not only manual tuning search frequency point, but also Fast intuitive observation of the frequency level characteristics of the EUT. This requires that the self-excited signal can not only test the specified frequency points, but also scan in a certain frequency range.
4. Different intermediate frequency filters:
Spectrum Analyzer: The resolution bandwidth is 3dB bandwidth of amplitude frequency characteristic.
EMI Receiver: The IF bandwidth is 6dB bandwidth of amplitude frequency characteristic. According to EMC standard, civil and military bandwidth are 6dB.
5. Different detectors:
Spectrum Analyzer: There are usually only peak and average detectors, but no quasi-peak detectors.
EMI Receiver: EMC standard requires test reception with peak, quasi-peak and average detectors.
6. Test accuracy:
the EMI receiver should have higher accuracy and lower distortion response than the spectrum analyzer. On the current market, there are some receivers that are modified from spectrum analyzers such as: General Spectrum Analyzer + Pre-selector + 6dB IF Filter + Three Detectors + Point Test Power + High Precision Signal Processing to be sales as “EMI Receiver”, the modified spectrum analyzers price is about 20-30% as EMI receiver
7. Whether can pass CNAS:
Whether it is a general spectrum analyzer or a modified spectrum analyzer, because its underlying hardware design completely does not meet the basic requirements of CISPR15/CISPR16, so they can’t pass the CNAS measurement and calibration of the China Institute of Metrology or Shanghai Institute of Quality Inspection and Technical Research (SQI). But EMI receivers are different. For example, LISUN’s EMI-9KB receiver has obtained a CNAS calibration certificates. (P.S. China CNAS is membership of iLac-MAC, if the instruments have CNAS calibrate certificate, it can be accepted in the whole world other countries when your lab were ready to authenticate/pass ISO17025)
Conclusion:
The advantages of the spectrum analyzer are to observe in a very wide frequency range, quickly test, it is economical. The disadvantages are poor test accuracy, small low-frequency resolution, large intermodulation interference, poor selectivity, and only single-peak detection mode, it can’t replace EMI receivers and can’t pass CNAS measurement and calibration.
The advantages of the EMI receiver are high test accuracy, large dynamic range, high frequency resolution, high sensitivity, small intermodulation interference, four basic detection modes, and the ability to obtain CNAS calibration and measurement that fully meet the requirements of CISPR15/CISPR16; the disadvantage is that it cannot Observing in a very wide frequency range like a spectrum analyzer (currently China domestic EMI receivers are up to 1GHz), it is impossible to quickly compare to the spectrum and amplitude of the signal under test, and the price is relatively high.
Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.