Electromagnetic interference is usually described as an electrical noise that can enter electronic equipment from a radio signal or other sources. It usually shows up differently depending on what we’re talking about. If we talk about audio, electromagnetic interference can show up as a hiss or hum. In video, it shows up as scrambled pictures and static, and as errors in data networks. Although sources of electromagnetic interference are all around us, if we are careful enough with the installation and use of our equipment, we can effectively “eliminate” the trouble-causing EMI.
Sources of the EMI
The electromagnetic interference comes from the radio part of the electromagnetic spectrum. Electric equipment usually picks up such unwanted signals like television broadcasts and radio, as well as those that are produced by fluorescent lights. These signals are usually powerful enough to interfere with our audio gear, computers, TV’s and many other devices. When experts are designing equipment they spend a lot of time ensuring that electromagnetic interference will not be an issue.
Earth Ground as a key solution
One of the most common and key solutions for the elimination of EMI is the use of earth ground. A direct connection to an electrical outlet ground should do the trick. Or even a cold-water pipe. The grounding point will act like a sink in which the energy of the electromagnetic interference will drain. The EMI will usually follow “the path of least resistance”. A good reason why the more professional and electric equipment comes with a three-wire power plug, is because the grounding wire helps reduce electromagnetic interference.
Optical Link is a good solution
The optical fiber cables are totally immune to the electromagnetic interference solely because they transfer pulses of laser light instead of the standard electrical signals. Radio and EMI will have no effect on these optical signals. However, fiber optics can be expensive when compared to copper wire.
What is a Balanced Line?
Long audio cables, for example, those made for microphones or guitars, are usually very prone to picking up the buzzing noises caused by electromagnetic interference. A connection that is called a “Balanced Line” will solve this problem. If you don’t know what this is already, it’s a connection that uses two wires that both carry signals which are equally strong but they have the opposite polarity. Any electromagnetic interference that enters the cable will appear as a positive signal on both of the wires. At the receiving end, a circuit will subtract both signals and will significantly reduce if not entirely eliminate the noise caused by EMI.
A metal shield or a screen will block the interference, especially if its barrier is connected to the ground. If we look at audio and video cables, for example, they have an inner conductor that is surrounded by a braided shield on the outward layer. The electromagnetic interference will enter the shield and will flow directly to the ground instead of messing with our signals that the cable is carrying. The best protection from EMI is a box called a Faraday cage. This cage is made out of a grounded metal sheet, hardware cloth or a wire, and it completely surrounds electronic devices, blocking all of external EMI. Faraday cages are largely used in science, industry and even medicine.