Calibration of a Semi-Anechoic Chamber for FCC Open Field Site Radiated Emissions Measurements

In 1981, Tandem constructed a semi-anechoic chamber with the goal of testing small systems and peripheral devices for compliance with the FCC limits for Class A (Commercial) computing equipment. This chamber, provided by Scientific Hardware, is 15.24 meters (50 feet) long, 9.92 meters (.26 feet) wide and 3.66 meters (12 feet) high (steel dimensions). RF absorber cones, provided by Advanced ElectroMagnetics Inc., ranging in length from .61 to 1.22 meters (2 to 4 feet), are mounted on the walls and ceiling with the 1.22 meter cones mounted in the center of the chamber (point of maximum reflection) and shorter cones at either end. The chamber saw little use other than for conducted emissions testing for some period of time due to a lack of knowledge about its correlation to an open field test site.