Most electronic equipment is, in some manner, affected by electromagnetic radiation. This radiation is frequently generated by such general purpose sources as the small hand-held radio transceivers that are used by operating, maintenance and security personnel, fixedstation radio and television transmitters, vehicle radio transmitters, and various industrial electromagnetic sources.
 
 
In recent years there has been a significant increase in the use of radio telephones and other RF emitting devices operating at frequencies between 0,8 GHz and 6 GHz. Many of these services use modulation techniques with a non-constant envelope (e.g. TDMA).
 
In addition to electromagnetic energy deliberately generated, there is also radiation caused by devices such as welders, thyristors, fluorescent lights, switches operating inductive loads, etc. For the most part, this interference manifests itself as conducted electrical interference and, as such, is dealt with in other parts of the IEC 61000-4 standard series. Methods employed to prevent effects from electromagnetic fields will normally also reduce the effects from these sources.
 
 
The electromagnetic environment is determined by the strength of the electromagnetic field. The field strength is not easily measured without sophisticated instrumentation nor is it easily calculated by classical equations and formulas because of the effect of surrounding structures or the proximity of other equipment that will distort and/or reflect the electromagnetic waves.