Abstract: An FM radiowave receiver includes a diversity antenna system responsive to signal strength and noise levels. The signal strength and noise detectors generate representative signals that are compared with a threshold value for determining the input to a control for the antenna switch alternately connecting two or more antennas to the front end of the FM receiver. The present invention provides an adaptive threshold for each of the signal strength and noise signals so that the switching is limited to significant changes in signal strength and noise levels. In the preferred embodiment, the noise level threshold is adapted as a function of the modulation level of the audio composite signal delivered from the FM detector to the FM stereo decoder of the receiver.