Hi Tim. You wrote: <If screened mains cable is used, then surly it acts like a coax (a poor one possibly) and transfers the energy, contained within, to a point where the cables are not shielded. This would probably be at the mains wall socket - where the energy could (would?) then radiate! If the intention is not to cause interference to radiocommunications etc. then how has the screened mains cable helped? The test might seem OK but how is "due diligence" served?>
My problems have been that filters are often guilty of resonances at particular frequencies, providing substantial gain rather than attenuation. With 'white noise' things like phase angle controllers in the box, these filters put (in one instance) 32MHz out on to the mains cable, which radiated beautifully. The screen was sufficient to drop those emissions by about 15dB, thereby bringing it back into compliance. The transmission line characteristics of screened three core cable are very poor, and the conducted emissions of the 32MHz past the mains lead were clearly very much reduced by the inductance/capacitance of the cable, in that the -15dB results were perceived. The radiated emissions included those from the mains supply to the equipment. The mains cable on this thing was 3 metres long, and made up from component's, not moulded. The screen was grounded at the Supply end. Interesting stuff... Chris Dupres Surrey, UK.
