Intrinsic sources of IM generation

In addition to avoidable sources of intermodulation signals introduced in manufacture or assembly of a multiplex system, there will be some sources inherent to the materials of which the system is constructed. At some point these sources must provide a lower bound to possible system sensitivity. Such a limitation will only be significant if it is reached before thermal noise becomes dominant. At 20 C and a bandwidth of 2500 Hz, the noise power becomes-140 dBm. It is potentially possible to lower either the temperature or the bandwidth by a factor of about 100, so an ultimate sensitivity limit of about-180 dBm is perhaps significant. Above these levels, a number of intrinsic IM mechanisms can be identified. This chapter constitutes a review of significant intrinsic IM sources.