Electromagnetic Test Engineering (Code 549.3)

Introduction

Two shielded/anechoic testing facilities are available for conducting EMC tests. These facilities meet electromagnetic performance requirements specified by MIL-STD-461, and support the performance of EMC tests specified by MIL-STD-461; the GSFC "Goddard Environmental Verification Specification" (GEVS); and numerous other EMC testing specifications. Both facilities provide very low interior noise level ambient electromagnetic environments; excellent earth grounding; and have the ability to contain internally-generated, radiated electromagnetic waves. The ambient electromagnetic noise level is verified to be at least 6 dB below test specification limits prior to testing. Both facilities feature ventilation and other apertures designed as waveguide-below-cutoff to prevent either ingress or egress of electromagnetic waves. All electrical power, communications, and other facility wiring are filtered, and the facility structures are bonded to earth ground, to minimize the introduction of external electromagnetic noise. Both facilities are equipped with electromagnetic energy-absorbing panels allowing optimized anechoic performance. Each facility also features wall-mounted ferrite tiles for absorption of incident energy at frequencies from 20-MHz to 1-GHz and the Small facility has ceiling-mounted tiles as well. The Large facility has only a 10-ft x 10-ft anechoic target mounted on the ceiling. It is typically used for the absorption of intentionally generated, highly directional test article microwave signals.

Integral Instrumentation

Hewlett-Packard (HP) and Rohde & Schwarz spectrum analyzers/receivers systems are used for generated interference data acquisition, processing, and data reduction. Peripheral equipment includes electric field and magnetic field antennas and line conduction transducers for testing in the frequency range 20 Hz to 40 GHz. The Receiver/Analyzers are controlled by an ISO9000 controlled, Windows-based EMI measurement software package.

Susceptibility tests are performed using a composite electric field, power, and signal line susceptibility system consisting of signal generators, amplifiers, and transducers for injection and radiation of electromagnetic energy. The test frequency range is 30 Hz to 400 MHz for signal injection, and 10 kHz to 40 GHz for signal radiation

Data Acquisition

All emissions test data are recorded in a swept spectrum analog format at specified receiver bandwidths. The data is then converted to a logarithmic amplitude versus frequency printout, including a specification limit when applicable, by an ISO9000-compliant software package. The measurement and analysis system is used for both radiated and conducted emissions measurements. All susceptibility data are acquired manually during the injection or radiation sweep. During testing, if the experimenter notes frequencies at which the test item is susceptible, these frequencies and threshold levels are recorded manually on data log sheets.

Auxiliary DC Electrical Power

Two auxiliary power systems are available which have the following capabilities. These DC systems are normally used to provide very low noise power to the test article to insure that any measured emissions are, in fact, generated by the test article and not the test equipment.

Low Power DC System - 50 amp maximum, 100 amp-hour portable battery system, 28 VDC, ±4 VDC

High Power DC System - 100 amp maximum, 600 amp-hour semi-portable battery system, 28 VDC, ±4 VDC; also contains special connections for 24 to 36 VDC in 2-volt increments.