ForewordANSI C63.4@ American National Standard Methods of Measurement of Radio-Noise Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 10 W to 1 GHz@ has undergone several revisions since the original document@ covering methods of measurement@ was produced in 1940. While many improvements were made in the standard from time to time@ the reproducibility of measurements of radiated interference from one test site to another has not been completely satisfactory.In 1982 a concerted effort was organized in Subcommittee 1 of American National Standards Committee C63 to determine how the technique could be improved. Evidence showed that the variability was due@ in part@ to inadequate (1) control of site ground plane conductivity@ flatness@ site enclosures@ effects of surrounding objects@ and certain other site construction features; (2) accounting for antenna factors@ associated cabling@ and balun and device under test characteristics; and (3) consideration of mutual coupling effects between the device under test and the receiving antenna and their images in the ground plane. Accordingly@ ANSI C63.4 was revised@ and C63.5@ C63.6@ and C63.7 were prepared to provide additional information. This standard provides guidance information on the calculation of the errors incurred in making tests on an open-area site.ScopeThis guide shows the basis for the acceptability criterion of ??4 dB for the site attenuation measurements required in ANSI C63.4 1992.