New-Tech Europe | Sep 2017 | Digital Edition

conformance parameter limits in the display to simplify EMC compliance testing. Preliminary testing for radiated emissions can be accomplished with a spectrum analyzer and an appropriate antenna. The spectrum analyzer should have the capability to make measurements from 30 MHz through at least 900 MHz. The ability of the spectrum analyzer to perform quasi-peak measurements and display conformance parameter limits in the display will make the preliminary testing tasks easier to perform. The antenna used for preliminary radiated emissions testing should have a bandwidth similar to the spectrum analyzer and the gain versus frequency characteristics needing to be known. It is preferable to be able to perform the radiated emissions testing in an electrically quiet room with at least three meters (10 feet) between the radiated emissions EMC antenna and the EUT. An initial measurement in the room with the EUT powered off will provide information regarding the ambient RF noise present during the testing. Most management teams appreciate projects completed under budget and ahead of schedule. Unfortunately, EMC compliance issues can be a common source of last minute budget and schedule increases for projects. Performing pre-compliance EMC testing during the system assembly phases of a project can help to eliminate those last minute changes to a design that impact budgets and schedules. Pre- compliance EMC testing also helps to ensure no issues arise during final compliance testing. Full service power supply vendors, such as CUI, have the equipment and experience to assist in power supply design and selection, including pre-compliance and final EMC testing.

Figure 3: Conducted emissions test set-up

Figure 4: Radiated emissions test set-up

impedance test port to monitor the conducted emissions from the EUT (Equipment Under Test). The spectrum analyzer used for conducted emissions testing can be a basic model with the ability to perform measurements from 150 kHz through 30 MHz. Many vendors of spectrum analyzers include the ability to perform quasi-peak measurements and incorporate

pre-compliance testing themselves the tests can be performed in a room with a minimal amount of test equipment. The equipment required for conducted emissions testing is an LISN (Line Impedance Stabilization Network) and a spectrum analyzer. The LISN is a passive network used to minimize the noise conducted from commercial power lines and also provides a controlled

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