SECURITY SYSTEM WITH INDUCTIVE TO RF COMMUNICATIONS LINKS

• US 3,573,620 A
• Filed: 05/31/1968
• Issued: 04/06/1971
• Est. Priority Date: 05/31/1967
• Status: Expired due to Term

• Current Assignee: Ashley John Raymond, Douglas Colin Grahame
• Original Assignee: Ashley John Raymond, Douglas Colin Grahame
• Inventors: ASHLEY JOHN RAYMOND, DOUGLAS COLIN GRAHAME
• Application Number:
  US04/733,693
• Time in Patent Office: 1,040 Days
• US Class Current: 340/525
• CPC Class Codes: G07C 1/20 Checking timed patrols, e.g. of watchman

Abstract

In a location system a radio transmitter carried by a security guard or watchman includes a loop aerial and a loop demodulator, and loop carrier frequency generators each generating a loop carrier frequency modulated by a different modulating frequency are installed at different points to be visited by the guard, so that as the guard reaches each point the loop carrier is demodulated and the modulating frequency is used to modulate the transmitter carrier. The transmitted signals are picked up at a distant monitoring point, demodulated, and the modulating frequency is identified with the point visited.

Claims

1. A security system comprising signal receiving and transmitting means to be carried by a watchman or security guard, a plurality of inductive frequency generating means for generating a loop carrier frequency and a predetermined location frequency for modulating the loop frequency, said generating means being located at selected points in the area to be patrolled by the watchman or security guard, said signal receiving and transmitting means comprising a loop aerial for receiving both the loop carrier frequency and the location frequency generated by said generating means as the said guard nears said generating means and a loop demodulator for demodulating the received signal, said signal receiving transmitting means being adapted to transmit the said demodulated signal to a second receiving means for receiving said signal, said second receiving means including a plurality of filters by which the particular location frequencies may be recognized, and indicating means for indicating the receipt of each particular location frequency by said second receiving means.

2. A system as claimed in claim 1 in which the radio transmitter is a V.H.F. transmitter.

3. A system as claimed in claim 1 in which the indicating means comprises an indicator panel having a number of windows each corresponding to one of the locations, a lamp behind each window, and means responsive to the recognition of the respective modulating frequency to cause the lamp to be illuminated.