CISPR standard up for a vote

EMC standard CISPR 16-1-1 Ed. 3 is open for voting by the national committees until November 20, 2009.

Martin Rowe, Senior Technical Editor -- Test & Measurement World, 10/8/2009 11:17:31 AM

The international EMC standard CISPR 16-1-1 Ed. 3 preview is now available. If approved, the standard for will allow EMI engineers to make compliance measurements below 1 GHz with a spectrum analyzer that lacks a preselector. The current Edition 2 requires you to use an EMI receiver that meets the standard's requirements. Edition 3 is open for voting by the national committees until November 20, 2009. If approved, CISPR 16-1-1 Ed. 3 should be published on or about December 31, 2010 (Ref. 1).

Werner Schaefer of Cisco Systems, who is project leader for Revision 3, explained that spectrum analyzers have advantages over EMI receivers and usually are less expensive, which is one reason that EMC engineers want to use them. But, spectrum analyzers must have certain features. "If a spectrum analyzer has the proper average and quasi-peak detector (down to 20 Hz) and meets all other stated requirements, then you can use it below 1 GHz," he said. "In addition, you must also demonstrate that the EUT [equipment under test] doesn't emit signals with repetition rates of 20 Hz or less to use a spectrum analyzer. Otherwise, you must use a fully compliant EMI receiver."

Schaefer explained that EMI receivers were required because they have preselectors (filters) on their front ends because they provide adequate dynamic range for quasi-peak measurements of low repetition rate signals and they prevent broadband signal overload to a large degree. You can, though, get results with a spectrum analyzer similar to those from an EMI receiver if you use the spectrum analyzer properly. You must take care when using spectrum analyzers on high amplitude signals and on signals with bandwidths that are wider than the instrument's IF frequency to avoid overloading the analyzer's front end.

Schaefer also noted that spectrum analyzers may sweep across a frequency spectrum more rapidly than traditional EMI receivers, which scan a spectrum in discrete frequency steps. Thus, emissions tests take less time with a spectrum analyzer, especially if you can use prescan measurement results to perform the final measurements only at frequencies with amplitudes close to or above the applicable limit.

"Spectrum analyzers let you see the entire swept-frequency range and they let you see how the EUT behaves," said Schaefer. "EMC engineers typically use a spectrum analyzer anyway to find the settings and cable layouts that produce the highest emissions. So, why not use it for compliance measurements?"

Reference
1. CISPR 16-1-1 Ed. 3.0, Specification for radio disturbance and immunity measuring apparatus and methods - Part 1-1: Radio disturbance and immunity measuring apparatus - Measuring apparatus. International Electrotechnical Commission, www.iec.ch.