A mobile phone hand-free extension device includes a FM radio transmitter with
an active frequency searching circuitry to utilize a vehicular FM radio receiver
for reproducing the audio signals from the mobile phone. The active frequency searching
circuitry in this invention automatically detects which frequency band the vehicular
FM radio receiver is currently using and set the RF frequency of the FM transmitter
to the detected frequency. The FM transmitter relays the audio signals from the
mobile phone by transmitting the audio signals through radio wave to the vehicular
FM radio receiver to be reproduced by the speaker of the receiver.
