Test & measurement
a common instrument of choice to quickly build an overall understanding of the emissions and interference sources, typically using a near-field probe. Typical checks include looking for obvious sources of noise including switching regulator noise or high-frequency PWM signals such as display and backlight drivers, harmonics of system clocks, noise coupled into ground planes or I/O lines, and unintentional antennas such as long PCB traces and cables. Less obvious problems include periodic spikes or broadband bursts, conducted emissions, and noise resulting from poor layout or split ground planes. On the other hand, intermittent or sporadic interference triggered by specific conditions can be difficult to find and special features like advanced triggering or real-time analysis are needed to capture time-correlated events. Some EMI issues like ground loops or cross-system coupling only emerge when multiple subsystems interact and may not be visible when probing individual boards. Overall, “sniffing around” the assembly with an old spectrum analyzer can be time consuming and may fail
Instrumentation Monthly May 2026
to discover certain types of problems. Sometimes, this approach needs a seasoned engineer’s experience to reveal elusive sources of unwanted noise.
EFFICIENT EVALUATION
A test receiver can detect and characterise diverse types of interference with ease. Equipped with CISPR-16 EMI detectors as standard and modern EMI debug features, it can detect time-varying or intermittent emissions that simple peak detection on an old spectrum analyzer would underestimate or miss entirely. Typically used in formal radiated and conducted emissions testing, this type of instrument is well suited to capturing standardised measurements and can accurately assess emissions to provide precise, full-compliant results. The test receiver can offer even greater help to engineers when equipped with tools such as real-time spectrogram, time- domain analysis, and click analysis for assessing discontinuous disturbances from electromagnetic switches such as relays and contactors. Although mandatory only for certain products as covered by CISPR 14, typically home
appliances, click testing can give valuable insights for debugging other categories of equipment that may not be subject to compulsory testing. Automotive systems are an obvious example, where motor-driven mechanisms such as fans and pumps, heaters, lighting, and others are constantly activated and deactivated during normal operation of the vehicle. Identifying and minimising these emissions can improve coexistence between the many systems on board. Clicks, which are short emissions and can be either sporadic or burst-like, are often difficult or impossible to detect using ordinary continuous scans. Analysis requires a test receiver that supports automated click counting and timing. This combines well with user-interface graphics that let developers zoom in on individual clicks, measure timing and amplitude, and correlate the clicks with specific operations in the equipment being tested. Automated analysis like this is faster and easier than checking raw EMI data, making debugging more efficient, and helps find intermittent signals that could otherwise be missed. By performing standard-compliant click rate
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