Chapter 1 Exercise: Examples of Electromagnetic Interference
These simple demonstrations can be performed in front of the class or assigned as a laboratory exercise. The goal is to provide common examples of electromagnetic interference that students may already have encountered. Students can be asked to identify the source, victim and coupling mechanism. They can also be asked to share their own experiences with similar forms of EMI.
A small, brushed DC motor interfering with a handheld AM radio
Virtually any brushed DC motor creates enough noise to be picked up by a portable AM radio. You can see a brief video demonstration by clicking here or on the image to the left.
A small digital device interfering with an FM radio tuned to a harmonic of the clock frequency.
Most electronic toys and computing devices emit power in the FM radio band that can be picked up with a nearby portable radio. This is true even when these devices meet federal radiated emissions requirements.
Some clock radio displays, scales, and electronic toys can be temporarily disabled by an ESD discharge.
Use an ESD simulator, or any other source of electrostatic discharge, to create latch-up in an electronic device. Some clock radio displays, scales, and electronic toys can be temporarily disabled by an ESD discharge. You may have to experiment a bit to find the right device for this demonstration. We suggest that you don't experiment on valuable items, because some devices can be permanently damaged by ESD.
An inconspicuous battery-powered signal generator can be used to block reception of any AM or FM radio station (or even a nearby cell phone) to demonstrate intentional EMI.
Use an RF signal generator, or a simple circuit that generates a digital clock to produce noise that drives two conductors relative to each other. Choose the frequency of the driving signal so that the fundamental or one of its harmonics falls on a frequency that is shared by an FM radio station in your area. Demonstrate that the radio station goes silent when the interfering signal is present.
