US Patent 9226189 Monitoring health of a predistortion system

At a current time, a current intermodulation content of a predistortion system is determined. An intermodulation ratio is determined using the current intermodulation content and a previous intermodulation content for the predistortion system. The previous intermodulation content is determined at a time previous to the current time. The determined intermodulation ratio is compared with stored intermodulation ratios. A warning is communicated in response to the comparing indicating the predistortion system is unhealthy. Apparatus and computer program products are also disclosed.