Signal transmission apparatus

Signal transmission apparatus is provided for a communications system, such as a cordless telephone system, having a plurality of transmitters (A1, B1, C1) for transmitting information signals over any one of several transmission channels, and a plurality of receivers (A2, B2, C2) for receiving the information signals over any one of the transmission channels. To establish a selected transmission channel between a particular transmitter (A,, B,, C1) and a particular receiver (A2, B2, C2), the transmitter (A1, B1, C,) selects an unoccupied transmission channel and transmits thereon a code identifying the receiver (A2, B2, C2) using a wide band signal for high speed bit transmission. When the receiver (A2, B2, C2) detects the presence of the identifying code over a particular channel, it first determines that the transmitter (A1, B,, C1) is the particular transmitter (A1, B,, C1) and, if so, establishes the transmission channel therebetween. The transmitter (A1, B,, C1) confirms that the transmission channel has been established, and then continues to transmit the identifying code repeatedly over the transmission channel using a narrow band signal with a low bit transmission rate. Both the wide band and narrow band signals containing the identifying code are included within the audio signal transmission band.