FM radio transmitter is being widely used in portable devices as a convenient way to output audio contents to ubiquitously available FM radio receivers in cars or homes. However, the signal from the FM radio transmitter may be interfering with the signal being broadcast by an FM radio station. A scan system is incorporated into the FM radio transmitter to quickly and reliably identify a vacant channel for the FM radio transmitter to use. The scan system measures on-channel and out-of-channel signal quality and selects a best channel for transmission based on the measured on-channel and out-of-channel signal quality. The scan system is also incorporated into an FM radio receiver to quickly and reliably tune to a valid channel. The scan system selects the valid channel based on the measured on-channel and out-of-channel signal quality.