ABSTRACT
One of the leading questions asked by people who have an EMI problem or are joining the EMI field is related to the source impedance. Several senior scientists and doctors of engineering have asked about the transfer function of a certain filter that RFI Corp. proposed for their application. They were going to measure the line impedance along with the load impedance and wanted to know the transfer function of the EMI filter that was designed in. The transfer function can be calculated, but most EMI filter manufacturers rarely measure them. If the filter manufacturer, here RFI Corp., could provide this information, this company was going to add another section between the filter and the load. The purpose would be to notch out resonant rises and other instabilities of the entire system. This procedure would work very well if they were assured that the line length, conductor spacing, or diameter of the conductor would not change much from installation to installation. These parameters require precious time to determine and could require expensive rental equipment for most companies. This would work well if their system, using the EMI filter device, were to be installed on one type of ship or aircraft, where these cable dimensions would be nearly the same. The technique would fail to work if the unit was installed on different vessels or used in various other applications. Also, they would need to have a look at all the possible load conditions, not just the peak load. If the device would go into some standby mode, the instabilities could shift and the filter along with the rest of the equipment could oscillate.
