Conformity Magazine - October 2008 - (Page 47)

here are many types of instrumentation in a fully equipped EMI/EMC test laboratory. In this article, we’ll highlight features to look for in the most commonly used equipment. Some of these are “must have” specifications, while others are more oriented towards convenience of use. Radiated Emissions Equipment for Interference and Radiated Immunity Spectrum Analyzers and Receivers The spectrum analyzer/receiver is the best known piece of equipment in the EMC lab, occupying a central place in interference measurement. These instruments vary widely in features and price. This variation is understandable when one looks at the major and less obvious features that may be incorporated or excluded (Table 1). These features interact in a number of ways. While additional features mean increased capability, they don’t have to mean increased complexity of operation. A lot depends on the user interface details, both in hardware and software, such as grouping of controls, logical hierarchy of functions (or lack thereof), programmability, and available software. Sometimes manufacturers will use the terms “receiver” versus “spectrum analyzer” to differentiate their products. This was especially true in years past, when there was a sharp T differentiation between products optimized for sensitivity, overload resistance, regulatory detector type (i.e., CISPR quasi-peak), and those optimized for quick use and a swept frequency display. The two most important issues were the issues of pre-selection and graphical display. Preselection is concerned with the front end of the measuring instrument. All of these instruments are superhetrodyne receivers. That means they contain a local oscillator and mixer stage, which shifts the incoming signal to a fixed intermediate frequency, where it is amplified, filtered, and detected. One way to build a superhetrodyne receiver is by connecting the mixer to the RF input without any intervening amplification or frequency selective circuitry. When this is done, the mixer determines two important areas of performance: 1) noise figure, and 2) out of band overload behavior. The two are related. The ultimate sensitivity of a receiving system is limited by its noise figure, which is in turn dominated by the first stage. A “good” amplifier stage can have a noise figure in the range of 3 to 6 dB. In contrast, the noise figure of the broadband diode mixers used in spectrum analyzers up to 2 GHz is more like 30 dB. This is the reason that preamplification is generally used ahead of the mixer stage for low-level EMI (e.g., Class B ITE) measurements. The question is as to how the preamplification is done. BE CURIOUS: A NEW COMPANY IS BORN. BE AWARE: AN ESTABLISHED EMC LEADER IS GAINING STRENGTH. Teseq for EMC Test Solutions: A new company combining tradition and experience with dynamic and innovative development. Teseq continues what Schaffner created, leading EMC solutions that are better by design! As an independent, management owned company, we focus with full commitment, profound know-how and continuous research on our core business: EMC test solutions and customized client support worldwide. Give us a challenge. Test us. Teseq, Inc., USA E-mail: usasales@teseq.com Tel: (888) 417-0501 Fax: (732) 417-0511 www.teseq.com formerly Schaffner Test Systems oCtober 2008 Conformity 7 http://www.teseq.com http://www.teseq.com

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Conformity Magazine - October 2008 Contents Editor's Note FCC Releases Annual Report on National Do-Not-Call Registry Commission Cracks Down (for the Fourth Time!) On Junk Fax Marketer FCC Releases Quarterly Reports on Consumer Inquiries and Complaints Greenpeace Ranks Electronics Manufacturers Standards List For The EU’s Energy Consumption Directive Published EU Commission Publishes Standards List for Directives on Pressure Equipment, Pressure Vessels Standards List for the EU’s Medical Devices Directive Available The IEEE Product Safety Engineering Society: The First Five Years ESD Open Forum Improving Election Security and Accuracy: The Future of Voting System Certification Conformity Assessment and Accreditation: Their Role in the Global Market Design Issues in Extreme EMC Environment Focus On... Test Equipment Buyers Guide Product News Updated Standards List for EU Directive on Active Implantable Medical Devices FDA Warns of Effects from CT Scans on Electronic Medical Devices FDA Provides Report Card on Its PMA Review Process CPSC Releases Import Safety Strategy Other CPSC Actions in the News IEC Standards Update Product Reviews UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - October 2008

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