IEEE Std ANSI-C63.22-2004 pdf download American National Standard Guide for Automated Electromagnetic Interference Measurements
The transducer and signal conditioning section of the system consists of all elements that are placed in front of the input connector of the EMI receiver. The function of this section of the system is to intercept the maximum signal levels emitted from the EUT, and transmit this energy to the receiver in a measurable form. These elements can include antennas or line impedance stabilization networks (LISNs), cables, the antenna selection RF switch (if multiple antennas are used to cover the appropriate frequency range), and any preamplifiers or attenuators (external to the EMI receiver) necessary to bring the signal levels to be measured to within the dynamic range of the receiver. In addition, included in this section is the antenna tower, and the EUT turntable, which are used to determine the maximum emission levels based on antenna height and polarization as well as EUT orientation relative to the measuring antenna.
Verification section The verification section of the emissions measurement system is necessary to ensure that data is collected with a functioning test system and the required tolerances, as per the applicable test specification, are met. The verification section consists of a stable signal source, which should be traceable to national calibration standards (e.g., NIST or other local standards reference organization), the associated cabling, and a dedicated manual or automated procedure. The verification procedure presents a means of quickly demonstrating that most elements of the measurement system, from the transducer output port to the data presentation, perform within previously defined tolerances that are acceptable by the standard to which testing is being performed. It should be noted that this process is not intended to be a detailed true test of the performance characteristics of the receiving system, but merely a means to check the tolerance of the frequency and amplitude calibration. It does not address many additional and important EMI receiver parameters.
A verification signal can be generated by a stand-alone signal generator, a receiver’s tracking generator, or a calibrated impulse generator. Verification, in its most simplified form, is performed by disconnecting the RF coaxial cable from the system’s receiving transducer, and connecting it to the verification signal source. The generator’s output frequency shall be tuned over the measurement frequency range of interest and its signal amplitude is measured by the EMI receiver. By comparing the current results with previously recorded and verified data, test system malfunctions can be identified quickly and a determination made if the resultant data still meets required tolerances. Once the verification process has been completed, the signal source is disconnected, and the system’s receiving transducer reconnected.