Analysis of repeatability and uncertainty issues in radiated emission tests regarding HDMI ports

This paper describes repeatability problem and uncertainty which occurs in radiated emission test according to EMC standard EN 55022 while Equipment Under Test (EUT) and Auxiliary Equipment (AE) are communicating by using High Definition Multimedia Interface (HDMI). Nowadays nearly all multimedia equipment has at least one HDMI port and this port is very sensitive in terms of EMC tests, especially in radiated emission test. Emission comes out from mainly the clock line during the tests. Therefore main frequency and its harmonics have a big effect on the test results. Many EMC laboratories are coming across a catastrophic problem when they want to arrange a robust setup according to standards, since there are several ingredients which have big influence on the test results. To compare the effect of HDMI cable and AE on the emission level, the same equipment (television as an EUT) was tested with different HDMI cables and auxiliary equipment. Also effect of HDMI cable position to emission level is tested by using same EUT and AE. The same problem is occurring easily when tests are performed according to new EMC standard EN 55032 which supersedes EN 55022 and EN 55013. To eliminate the effect of cable positions and to ensure the setup remains stable, disturbance values emitted from the cable at HDMI clock frequency and its harmonics were measured by using disturbance power test setup according to CISPR 16-2-2. Whether EUT has low emission or not, the EUT can pass or fail radiated emission test. When you repeat the tests even in the same laboratory, results are in a wide range of margins with an unacceptable uncertainty budgets.