Conformity Magazine - July 2008 - (Page 37)

ith an increasing number of EMI standards that require emission measurements above 1 GHz, more and more EMC test laboratories are confronted with the specific measurement difficulties encountered in this frequency range. One of the most common issues is the system sensitivity of the measurement system which effectively determines the minimum signal amplitudes that can be measured with a given system. Some standards like ANSI C63.4-2003, clause 8.2.4, require that the system sensitivity be determined before testing commences. In clause 4.1.5.4 of the same standard it is stated that the system noise floor has to be 6 dB lower than the applicable limit in the frequency range above 1 GHz. In order to meet this requirement, many test houses add a preamplifier to the test system to improve the system noise floor. However, the use of a preamplifier has a direct impact on the dynamic range of the test system and requires some considerations to ensure that a suitable amplifier is selected. Instrumentation Sensitivity The limitation of measuring radiated emissions, particularly in the frequency range above 1 GHz, is very often the noise floor of the test system. One contributing factor to this noise floor is the noise generated within the spectrum analyzer or EMI receiver itself. This noise, generated by the random electron W motion in various circuit elements, is amplified by multiple gain stages in the instrument and appears on the display as a noise signal. With spectrum analyzers and modern EMI receivers, this noise is commonly referred to as the displayed average noise level, or DANL. This noise power ultimately limits the ability to make measurements of low-level signals. If a 50 Ω termination is attached to the instrument input to prevent any unwanted signals from entering, then this passive termination generates a small amount of noise energy equal to kTB, where: k = Boltzmann’s constant (1.38 x 10-23 Joule/°K) T = temperature (°K) B = bandwidth in which the noise is measured (Hz) Since the total noise power is a function of measurement bandwidth, the value is typically normalized to a 1 Hz bandwidth (i.e., equivalent noise bandwidth). Therefore, at room temperature, the noise power density is 174 dBm/Hz. When this noise reaches the first gain stage in the analyzer, it gets amplified and the instrument also adds some of its internally generated noise. As the noise signal passes on through the system, it is typically high enough in amplitude that the noise generated in subsequent gain stages adds only a small amount to the total noise power. The input attenuator and one or more mixers may be placed between the input R Magnetic Shielding That Works! MuShield is a small company that tackles big problems. Our team is a talented mix of engineers with extensive experience in the field of magnetic shielding. This enables us to build, test, and deliver a product that works within a reasonable time frame. Visit us online at www.mushield.com. EMI Shielding & Design Magnetic Shielding Materials Sheet Coil Seamless Tubing R MuMetal2 Permalloy R HyMU80 R Manufacturing Capabilities Heat Treatment Design Capabilities Performance Testing Production Capabilities Shielding Consultation Prototyping Custom Electronic Components Shielding The MuShield Company 9 Ricker Avenue Londonderry, NH 03053 Toll Free: 888.669.3539 Email: info@mushield.com JULy 2008 Conformity 37 http://www.mushield.com http://www.mushield.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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.