GB1255296A - Subscriber's telephone instruments - Google Patents

Abstract

1,255,296. Radio signalling; substation circuits. INTERNATIONAL STANDARD ELECTRIC CORP. 11 June, 1970 [16 June, 1969], No. 28278/70. Headings H4K and H4L. In a cordless telephone comprising radio units in the handset and in the instrument body on which the handset rests when not in use, speech signals being conveyed from the handset to the body and from the body to the handset on first and second carrier frequencies respectively, the body includes a threshold circuit which detects when the received first carrier falls below a predetermined level and causes a special signal to be transmitted by the second carrier frequency to the handset to indicate to the user that the handset is too far from the instrument body. Such detection by the threshold circuit may operate a trigger circuit to disconnect the speech signals received from the handset from a hybrid in the body so that the resulting lack of sidetone in the handset receiver forms the special signal. Alternatively the trigger circuit may disconnect the speech signals received from the subscriber's line from the radio transmitter in the body, the resulting lack of speech signals in the handset receiver forming the special signal. In a further arrangement the trigger switches on a tone generator and connects it to the radio transmitter in the instrument body.