an analog signal the radio frequency of the fm transmitter is controlled in such a way that it starts from the lower band edge of the commercial fm band such as 88 108 mhz and increases repeatedly by a predetermined frequency step to the upper band edge the preferred predetermined frequency step can be the allocated channel bandwidth of an fm station at each frequency point the fm transmitter will send out the modulated rf carrier if the frequency of the fm transmitter matches that of the fm radio receiver 16 the signal with a particular pattern at the audio frequency will be demodulated retrieved and broadcasted from the speaker 17 that is connected to the fm radio receiver the microphone 11 picks up the audio signal from the speaker and sends it to the active frequency search unit to determine if this audio signal is the same as the particular signal that the fm transmitter originally sent out fig2 shows a flow chart for automatically searching the frequency of an fm radio receiver according to the present invention as shown in fig2 the frequency stepping process the signal emitting process and the signal comparing process are repeated over and over again until the original signal sent out by the frequency searching unit is received by it again when this condition is met the rf frequency of the fm transmitter is locked on to that.