ABSTRACT
A stray field will not cause electromagnetic interference (EMI) if it is very weak compared with the desired field, which might be the field of a broadcast signal. The permissible strength of the stray field depends on the strength of the desired field; the stronger the desired field, the more stray field can be tolerated. Unlike most electrical engineering topics, EMI control is not precise because of the complexity of practical hardware. It is virtually impossible to predict interference more precisely than within a factor of three, and usually the margin of error is even worse. Measurements can vary significantly between two supposedly identical samples, due to slight variations in physical dimensions. If one measures the EMI resulting from two different designs, the design that exhibits less EMI is probably better, but not always. An engineer can often judge if an EMI problem exists, but one must never rely on the accuracy normally expected in other branches of electrical engineering.
