t is essen- tial to be sure what will constitute acceptable performance and what 23.10.1 The EMC directive is a test failure. The relaxed EMC regime that had hitherto existed throughout 23.9.3 Emissions Europe, with the exception of Germany, has now changed dramati- cally. In accord with the general objective of the single European By comparison with immunity requirements, equipment emissions market, the European Commission has put forward an EMC direc- are relatively easy to characterise. The majority of emissions from tive (89/336/EEC) (EEC, 1989) whose purpose is to remove any electronic equipment are due to either switching or other electro- barriers to trade on technical grounds relating to EMC. Thus, EC mechanical operations, or digital clock and data lines. The former member states may not impede, for reasons relating to EMC, the can be pulses at mains frequency, such as from thyristor phase free circulation on their territory of apparatus which satisfies the controllers, motor commutator noise, individual switching 'clicks' directive's requirements. or switch mode power supply harmonics, and they are generally conducted out of the equipment via the mains lead. These emissions have been regulated for many years in order to 23.10.1.1 Scope and coverage minimise interference to AM broadcast and communications ser- vices. The directive applies to all electrical and electronic equipment Digital equipment with high frequency square wave clocks gener- placed on the market or taken into service, SO that it includes ates noise into the hundreds of MHz. The system clocks and their systems as well as individual products. It operates as follows: it sets harmonics are the principal source because their energy is concen- out the essential requirements; it requires a statement to the effect trated into a narrow band, but wideband noise from the data and that the equipment complies with these requirements; and it pro- address lines is also present. The noise amplitude and spectral vides alternative means of determining w