IDLE-BUSY SIGNALLING BETWEEN
TELEPHONE SYSTEM AND RADIOPHONE
 Inventor: John R. Barkwith, Hauppauge, N.Y.
 Assignee: RCA Corporation, New York, N.Y.
 Appl. No.: 830,856
 Filed: Sep. 6,1977
 Foreign Application Priority Data
Aug. 23, 1977 [CA] Canada 285341
 Int. C1.2 H04M 7/00; H04M 3/22;
 U.S. CI 179/2 E; 325/5;
 Field of Search 179/2 E, 2 EA; 325/2,
325/3, 5, 8, 15, 51, 55, 133, 364; 343/175, 177
 References Cited
U.S. PATENT DOCUMENTS
2,773,977 12/1956 Hale 325/364
3,105,881 10/1963 Maurushat 179/27 G
3,946,315 3/1976 Tustison 325/55
Primary Examiner—William C. Cooper
Assistant Examiner—Kenneth A. Chayt
Attorney, Agent, or Firm—H. Christoffersen; Samuel
Cohen; Carl V. Olson
An interface unit for use between a telephone system in which a single-frequency tone is transmitted in both directions when the circuit is on-hook (idle) and a single-channel-per-carrier radio system in which the radio frequency carrier is not transmitted when the circuit is idle. A transmitting portion includes a single-frequency tone detector means responsive to termination or initiation of the tone from the telephone system to turn on the radio frequency carrier. A receiving portion includes a radio frequency carrier detector means operative to switch the telephone system from the output of a local single frequency local oscillator to a voice frequency line from the radio system, and a single frequency detection means to switch the telephone system back to the output of the local single frequency oscillator.
8 Claims, 3 Drawing Figures