are commonly used in the art for various types of receivers including amplitude modulated signal receivers and frequency modulated signals receivers it is common for the threshold level of the squelch signal to be adjustable by means of a potentiometer not shown or other similar control adjustment of the squelch threshold adjusts the threshold signal strength of an active signal frequency that will be received by the scanner audio frequency circuit 10 amplifies the aforementioned audio signal and drives speaker 11 audio frequency circuit 10 also receives a muting signal mute from controller 12 which enables and disables the output of audio circuit 10 thereby enabling and disabling the audio signal reproduced by speaker 11 controller 12 may comprise an 8 bit central processing unit together with memory including ram rom and eeprom and peripheral input output circuitry the hitachi model h8 338 is suitable for example in fig1 a separate channel memory 13 is shown however the channel memory may be a part of the aforementioned memory circuits comprised within the controller 12 in the preferred embodiment eeprom is used because of its non volatile attribute channel memory 13 is shown as a separate entity in fig1 for clarity only a keypad 14 is coupled to the controller 12 in the preferred embodiment the keypad serves as an input device.