Different vehicle, same statistical transfer function?

Products containing electronics must generally be tested for electromagnetic susceptibility at the end of their development cycle. However, the earlier that the product as a whole, or the components and electronic sub-systems that might form part of the product, can be tested for susceptibility, the more benefit can be gained from such a procedure. One way in which this can be achieved is to test the individual components and sub-systems early in the design process of the product. For example in the automotive industry, individual systems can be tested using a bulk current injection (BCI) bench test. The difficulty in the correlation of these test results with those that are found when the system is installed in the finished product has previously been overcome by the use of a statistical technique. However, at present, the described approach has only been used and verified with transfer function data from vehicles of the `large car´ class. Since any recommended test procedure has to cover all sizes of vehicles, it is necessary to examine transfer function data for these vehicles. It is important to find out whether the same statistical data set can be used for all classes of vehicle. The aim of this work is to compare the statistical interpretation of transfer functions for different classes of vehicle. The authors earlier study (1991) was based on data exclusively from vehicles in the `large car´ class. This has now been compared with data for small cars (such as Rover 100) and 4×4 vehicles (such as Range Rover). The data considered is restricted to that recorded over the frequency range of 25 to 400 MHz, i.e. the applicable range for the bulk current injection (BCI) test