An apparatus, method and computer program product is disclosed. The apparatus may comprise means for transmitting and receiving radio frequency signals using a radio system coupled to an external antenna via an additional combiner or diplexer, means for receiving one or more reference signals usable for measurement of passive intermodulation from one or more nodes provided in a signal path external to the radio system, a first one of said nodes being associated with a signal path between the additional combiner or diplexer and the external antenna, and means for performing passive intermodulation cancellation based on the received one or more reference signals, including a first reference signal from the first node.