公开(公告)号：KR880000627B1

公开(公告)日：1988-04-18

申请号：KR820002057

申请日：1982-05-11

Applicant: MOTOROLA INC

Inventor： EOKLUND LAWRENCE M

IPC: G01R19/00 ,  G01R19/165 ,  G01R23/177 ,  H04B1/16 ,  H04H1/00 ,  H04H20/49 ,  H04L27/00 ,  H04H5/00

Abstract: The received signals are filtered to eliminate all signals at frequencies apart from the predetermined frequency. The filter output is coupled to a latching circuit which provides one output signal when a given number of cycles having a given amplitude have been detected in sequence, and a second output signal when a given number of cycles is lacking or of insufficient amplitude. If the filter output includes one or more cycles of the given amplitude followed by a longer series of cycles having less than the given amplitude, a timer is enabled to that any subsequent pulse of the given amplitude will block any detect signal for a predetermined period.