Conformity Magazine - July 2008 - (Page 17)

configurations as the NSA method, it reduces uncertainties due to fewer number of steps in the measurement process. In many cases “prime“ sites do have a ground plane size and test setup that has an impact on the accuracy of the measurements. Therefore, the RSM method may require carrying out several measurements at different locations on the groundplane, and the determination of the result may involve an averaging technique. The advantage of RSM is that the achievable accuracy is higher compared to the NSA method, since the uncertainty introduced by the antenna factors is eliminated. That could lead to a reduction of the acceptance criterion. If this is not done then sites which have a worse performance could actually pass with RSM. The NSA method avoids the use of hybrid antennas for site validation mainly because their phase centres vary over the frequency range, leading to difficulties in keeping the uncertainties as low as for separate biconical and log-periodic antennas. The advantages of RSM will therefore lie in the reduction in the number of measurements because antenna factors are not required. In the place of multiple measurements in NSA, only one site attenuation measurement per geometric configuration is required for the RSM. Furthermore, it is conceivable that hybrid (instead of biconicals and logperiodic) antennas could be used for RSM with an acceptable uncertainty. It is important to note at this point that, while traceability for antenna calibration and site validation has been solved, emission measurements still do not define reference antennas, and this problem remains to be solved. Fully anechoic rooms (FARs) are defined as having all six surfaces treated with absorbing materials and therefore do not have a ground plane floor like their counterparts, the semi anechoic chambers. CISPR 16-1-4 describes the chamber validation method known as the Free Space NSA, or FSNSA method. The FSNSA test uses a pair of antennas to validate the FAR, but differs from NSA in that there are restrictions on the antennas that can be used. The transmit antenna is specified by the standard as having to be a small biconical, no larger than 40cm in length covering the whole frequency range of 30-1000MHz. Although the receive antenna type is not specified by the standard, it must be the same antenna that will subsequently be used for product testing and is therefore most likely to be a single antenna, combining biconical/logperiodic elements, that will also cover the range 30-1000MHz. The reference site method described in the standard results in a single free space antenna factor that can be used for all positions, and which is therefore a relatively quick and simple calibration to carry out. 901 Sheldon Dr., RTP (Cary), NC 27513 USA JULy 2008 Conformity 17 http://www.productsafet.com http://www.productsafet.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - July 2008

Conformity Magazine - July 2008 Contents Editor's Note FCC Adopts 6 Million Dollars in DTV Enforcement Orders Commission Enforcement Bureau Adopts V-Chip Consent Decree FDA Seeks 2 Million Dollars from Medical Device Manufacturer FDA Answers Questions About CFLs and UV Radiation EPA Issues Energy Star Specs for TV, Video Boxes Canada Unveils Sweeping Product Safety Legislation How the Evolution of CISPR Standards Continues to Shape the Requirements for Anechoic Chambers ESD Open Forum Reach Compliance for Non-EU Article Manufacturers The iNARTE Informer Preamplifier Considerations for Emission Measurement Systems Effective Shielding in Medical Electronics Applications Product News Focus On...Power Components Buyer's Guide Updated Standards List for the EU's ATEX Directive EOS/ESD Symposium Set for September CPSC Actions in the News Researchers Work to Develop Non-Flammable Batteries Safety Link Launches Redesigned, Enhanced Web Site IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - July 2008

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