Abstract: An apparatus for communicating using multiple channels. The apparatus includes a first radio receiver and a controller. The first radio receiver is configured to produce a first receive signal in response to a first radio frequency signal in a first frequency band. The controller has a first receive input for receiving the first receive signal, an audio input for receiving an audio in signal, a selector input for receiving a selector signal, an audio output for producing an audio out signal and a first transmitter output for producing a first transmitter signal. The first transmit output is configured for communication with a radio transmitter operable to transmit a second radio frequency signal in a second frequency band different from the first frequency band.

Abstract: An apparatus and method for detecting the presence of a signal component in an arbitrary signal, where the signal component has a desired frequency. The apparatus includes an error signal generator and a detector. The error signal generator has an input for receiving a reference signal having a reference frequency, a second input for receiving the arbitrary signal having the signal component and an output for generating a difference signal dependent upon a difference in frequency between the reference frequency and the desired frequency. The detector has an input for receiving the difference signal and an output for producing a detector signal when the magnitude of the difference signal is greater than a threshold magnitude. The detector signal indicates the presence of the signal component in the arbitrary signal.