Conformity Magazine - October 2008 - (Page 45)

The SSPA needs no time to warm up, so does not need to be left on for stability. In addition, SSPAs typically have much lower thermal noise signature than TWTAs, and the harmonic and intermodulation content of solid state amplifiers is typically much less than that of tube amplifiers. Chambers and Screen Rooms The use of anechoic chambers and screen rooms, when available, can minimize both the effects of ambient electromagnetic signals on equipment and reduce the potential emissions from getting into the ambient environment. Typically, low noise work is performed in a screen room, and any power work is done outside of a screen room. High-power leakage in a screen room just creates a microwave oven. Once the environment is free of extraneous RF, it is important to keep it that way. Cell phones and other transmitting devices won’t function within a screen room, and will only contribute to the EMI, so they should be left outside. Environment Characterization In some cases, it may be difficult, expensive, or impossible to reduce or eliminate potential EMI sources from impinging on measurements. In those situations, characterization and publication of known local frequencies of interference can reduce troubleshooting time. Signals are to be expected in the AM and FM radio bands and mobile phone frequencies, and, if the location is near an airport or public safety office, additional frequencies can be expected. Researching the environment and verifying signal presence and type in a published list can save time in the future. Design Actions During the design stages, the use of various techniques can reduce interference opportunities not only during the development stage, but also when the product is complete and in production. Circuit shielding, prudent use of RF and microwave absorber material, and compartmentalization and filtering are all effective methods for containing and reducing interference. Implementation of capacitive and Pi filtering elements to reduce conducted interference are also key. The inclusion of DC-DC switching regulation adds another dimension of potential interference to be evaluated, particularly on the conducted emissions. Summary RF/microwave amplifier laboratories are among the most challenging EMI/EMC environments. RF is everywhere and, in a world dominated by electronic devices, it is not only naive but impossible to ignore the effects that both intended and unintended electromagnetic interference can have on the development and manufacture of electronic products. Fortunately, most of the issues created by interference can be easily and effectively resolved with the use of proper procedures and techniques during both the development and production stages. In most cases, these interference issues can be resolved or prevented using common sense. Take proper precautions. Communicate with team members. Identify concurrent testing. Know what to expect. Rationalize the results. If the results don’t make sense, investigate. Document anomalous performance with detail. Keep power levels as low as is reasonable. Reduce harmonics and intermodulation products. Most importantly, know the surrounding environment and know the products being developed and tested. Scott Behan is vice-president of marketing at CAP Wireless, Inc., and can be reached at scott.behan@capwireless.com. References 1. Broeders, Jan-Hein, Mark Meywes, and Bonnie Baker, “Noise and Interference,” Burr-Brown Design Seminar, (www.conformity.com/2261). RF Cafe, Noise Power & Voltage, (www.conformity.com/ 2262). Agilent Technologies, Inc., “Noise Figure Measurement Accuracy – The Y-Factor Method,” Application Note 57-2, (www.conformity.com/2263). 2. 3. FAST Link www.conformity.com/2260 oCtober 2008 Conformity 5 http://www.conformity.com/2261 http://www.conformity.com/2262 http://www.conformity.com/2262 http://www.conformity.com/2263 http://www.conformity.com/2260 http://www.okaya.com http://www.okaya.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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