Radiated Emissions

Pre-Compliance Radiated Emissions testing evaluates a design for the unintentional release of energy via an electromagnetic field. These fields can be generated by problems with layout, grounding, enclosures, cabling, and other structures that may be acting as unintentional antennas across the frequency band. Ultimately, the goal is to make sure the design will pass a full compliance test once it is ready for production. Radiated emissions are radiated through the air, so there are two main ways to test for them:

1. A near field probe helps us visualize potential sources of error by only picking up signals close to the probe head and in the correct orientation. This helps us to identify parts of our board or product that our actually emitting the problem signals. Using a calibrated far field antenna an engineer can closely approximate a full compliance test creating reliable measurements on the amplitude of the signals in question. Comparing these power levels to the relevant compliance limits enables an engineer to understand how much headroom they have in their design and ultimately whether or not it will pass a compliance test.

2. One other aspect of radiated emissions is cable emissions testing. Connected data cables such as USB or HDMI can act as antennas as well. Current clamps and probes as well as amplifiers may be needed to fully characterize these emissions. Having these cables attached and powered up can make a significant difference in near and far field measurements. Cabling should always be considered when testing emissions.

Even the simplest sensors and communication protocols need to be characterized before sending an IoT device to market. Characterize error budgets for timing, radio power, and modulation settings in a real environment before critical baseband data errors effect performance. Use a Spectrum Analyzer’s real time bandwidth to analyze the RF signal.

Conducted Emissions

Pre-Compliance Conducted Emissions is how engineers test for unintended power that gets coupled or transmitted back into the power line. The focus these regulations is to make sure the power line remains ‘clean’ and that other devices on the circuit and the power grid won’t be effected.

To isolate the measurements from the power line noise and provide a stable impedance for these measurements a LISN or Line Impedance Stabilization Network is used. Additional hardware such as attenuators and transient limiters may be used to optimize the measurement system to test a certain device. Pre-Compliance testing of conducted emissions helps engineers avoid costly errors in their power supply design or procurement. For engineers selecting an off the shelf AC-DC power adaptor for their product, a basic conducted emissions test can make procurement decisions easier and eliminate surprises at the compliance lab.

RIGOL Spectrum Analyzers and S1210 EMI Pre-Compliance software can be configured to adjust for correction factors from LISNs, attenuators, and other devices. This enables engineers to confidently take their product to a compliance lab with high confidence of passing the first time.

Immunity

Immunity tests a product’s ability to function when in close proximity to electromagnetic fields. There are two main types of signals used to test a product’s immunity:

1.Modulated waves – Often AM modulated waves across the frequency ranges of interest. These waves test the product’s ability to ignore power at frequencies that may be coupled into the device over time. These signals may effect a product’s communication, reliability, or logic.

2.Pulsed and Burst waves – These transients affect a device immediately and can cause a number of power and functional issues. Electrostatic discharge or ESD testing is a common type of transient immunity testing. These fast pulses can have different effects on a product and need to be considered as a potential source of reliability and functional issues.

In addition to RIGOL’s other Pre-Compliance instrumentation, immunity testing requires an RF source to generate high power modulated waves. Other types of equipment may need to be purchased for transient generation.