Devices Which Switch Faster Than 200 Hz
- Computers and other digital electronic equipment. These devices create and use signals which are switched on/off at great speed. It is the case that any repetitive signal can be reduced down to a Fourier series of sine waves. It so happens that a perfect square wave is
E = Eo sin (ωt) - {Eo sin (2ωt)}/2 + {Eo sin (3ωt)}/3 ......
As the term goes on for ever to higher and higher frequencies the square wave contains harmonics of the fundamental which go on upwards in frequency for ever, these harmonics are responsible for much of the interference created by computers. Always remember that a modern PC is a device which is operating in the VHF/UHF using square waves. As the cases on many computers are not perfect shields, some of this radio frequency energy can leak out and cause interference to radio (and sometimes TV) reception.
- Switch mode power packs can be a source of interference. These are used in consumer electronic/electrical products and in some lighting systems.
Read more about this topic: Television Interference
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