Touch-Tone encoder unit for mobile radio transmitter

Abstract

A Touch-Tone encoder unit for a mobile radio transmitter, or the like, is provided, which includes a keyboard and an encoder generator connected thereto which generates two distinct tones whenever a particular button on the keyboard is depressed and which identify the particular button. The dual tones are transmitted to appropriate receiving equipment where they are decoded, so that by depressing a number of pushbuttons on the keyboard in a particular sequence, a call may be placed. The unit of the invention may include a timing circuit which limits the length of each dual tone generated by the encoder generator to make the duration of each dual tone independent of the length of time the individual pushbuttons are depressed, the actual duration of the individual dual tones being sufficiently short so as to reduce the error rate substantially, especially where the radio transmission path is poor. In addition, the encoder unit of the invention may include an amplifier for raising the level of the dual tones generated by the encoder generator sufficiently to permit the tones to be reproduced by a speaker for monitoring purposes, so that the user can determine whether or not the tones are being correctly generated as the pushbuttons of the keyboard are operated. Easily adjustable level controls are also provided in the unit to permit the level of the dual tones introduced to the monitor speaker and to the transmitter to be individually and easily adjusted without any necessity for the encoder itself to be disassembled.

Dependencies are inferred from the claim text.