Nice article written by Ken Wyatt. See full article written HERE.
Snippets of text from article:
Wyatt Technical Services
As an EMC consultant, it seems that lately I’ve run into many client projects where radiated immunity has cropped up as the major issue. One reason for this may be the trend in using digital and analog circuits that are powered by 3.3 volts, and lower, which decreases noise margins significantly. Sensitive analog circuitry is also greatly affected.
The compliance testing for radiated immunity for most commercial products is based on the international standard, IEC 61000-4-3, and is usually performed from 80 to 1,000 MHz (sometimes to 2,000 MHz) at e-field levels from 3 to 20 V/m, depending on the product environment or application. Some military, vehicular or aerospace applications require testing to 200 to 1,000 V/m, and frequencies up to 18 GHz or more.
The RF signal is generally modulated by a 1,000 Hz AM sine wave modulation set to 80% for commercial testing, and short duration (as little as 1%) pulsed modulation for military and aerospace testing. The modulation is designed to test for “audio rectification” issues. For example, if the 1000 Hz modulation is rectified by semiconductor junctions, or in audio or other analog circuitry, it could cause bias upsets, or otherwise upset sensitive analog circuitry. For military applications, the pulse modulation serves to simulate radar interference.