Differences between EMC receiver and spectrum analyzer in EMC testing

When selecting EMC test equipment, we often encounter the following questions: What is the difference between an EMI receiver and a spectrum analyzer? Why should we use a receiver for EMI testing? This article analyzes the test principle of a receiver based on CISPR16-1 (GB/T6113) and GJB152, and provides a reference for the selection of receivers and spectrum test equipment - a receiver that meets the standards is the only choice for EMC conformity assessment testing. This article introduces the differences between a receiver and a spectrum analyzer.

The difference between receiver and spectrum analyzer

Spectrum analyzer is the main tool for spectrum analysis at present, especially the swept frequency heterodyne spectrum analyzer is the mainstream of spectrum analyzers today. It uses swept frequency measurement technology to obtain heterodyne signals through swept frequency signal sources for frequency domain dynamic analysis.

The receiver is the main tool for EMC testing. Based on the point frequency method, the principle of local oscillator tuning is used to test the level value of the corresponding frequency point. The scanning mode of the receiver should be obtained by step frequency tuning.

a. Basic principles

According to the working principle, spectrum analyzers and receivers can be divided into two categories: analog and digital. Heterodyne analysis is the most widely used receiving and analysis method. The following is an analysis of the main differences between heterodyne spectrum analyzers and receivers.

b. Front-end processing of input RF signal

The receiver and the spectrum analyzer process the signal differently at the input.

The signal input of the spectrum analyzer usually has a set of relatively simple low-pass filters, while the receiver must use a preselector with strong anti-interference ability for broadband signals. Usually, it includes a set of fixed bandpass filters and a set of tracking filters to complete the preselection of the signal.

Due to the influence of RF signal harmonics, intermodulation and other spurious signals, spectrum analyzers and receivers will have test errors. Compared with spectrum analyzers, receivers require higher accuracy, which requires an additional preselector at the front end of the receiver to improve selectivity.

The selectivity of the receiver is clearly defined in GB/T6113 (CISPR16).

c. Adjustment of local oscillator signal

In today's EMC measurements, people not only require the ability to manually tune and search for frequency points, but also need to quickly and intuitively observe the frequency level characteristics of the EUT. This requires that the local oscillator signal can test the specified frequency point and scan within a certain frequency range.

The spectrum analyzer realizes the swept frequency measurement through the swept frequency signal source. The swept frequency signal source is usually controlled by a ramp wave or sawtooth wave signal to scan within the preset frequency span to obtain the desired mixed frequency output signal.

The receiver frequency scan is step-by-step, discrete, and is a discrete point frequency test. The receiver scans at the frequency preset by the operator.