Chapter 13 – EMI to Consumer Electronics

This chapter introduces the term “Consumer Electronics” and analyzes interference to audio equipment, whether stereo high-fidelity equipment or the intercom is used to announce front-door visitors. Audio interference is probably the only form of interference where the equipment owner is totally responsible for the fix. The source of the problem of audio rectification is that there are PN junctions in the circuit, or that the amplifier may be driven into nonlinearity by the RF signal, detecting the AM signal as if it were a diode. It is the interconnecting wires that form the basis of EMI problems in stereo systems. The input wires are shielded, but often not to RF standards. The speaker leads are usually not shielded and are often far too long. That makes them act like an antenna for any frequency, where they are a substantial fraction of a wavelength. The key to troubleshooting this problem is to note whether the volume control has an effect on the interference signal. Also, common-mode and differential mode filters should be used to get rid of the interference. Shielding and grounding of equipment, as methods of avoiding EMI, are also discussed in this chapter.