WATCHMAN{3 S RADIO LOCATION INDICATING SYSTEM

• US 3,577,079 A
• Filed: 05/31/1968
• Issued: 05/04/1971
• Est. Priority Date: 05/31/1967
• Status: Expired due to Term

• Current Assignee: Douglas Colin Grahame, Horstmann Kenneth John
• Original Assignee: Douglas Colin Grahame, Horstmann Kenneth John
• Inventors: HORSTMANN KENNETH JOHN, DOUGLAS COLIN GRAHAME
• Application Number:
  US04/733,675
• Time in Patent Office: 1,068 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 has a modulator and an oscillator, but without the frequency determining components. At various points which the guard is required to visit are sets of frequency determining components carried in wall boxes, each set of components providing a different modulating frequency. The guard plugs in a lead from the transmitter at each point and the modulated carrier from the transmitter is received at a remote location, demodulated, and the point at which the modulating frequency was generated is identified.

Claims

1. A location system comprising a radio transmiTter to be carried by a watchman or security guard, the radio transmitter including an oscillator and a modulator for modulating the transmitter carrier wave but without a frequency determining element for the modulating frequency, means by which the modulator may be connected to any one of a number of frequency determining elements located at different points, each frequency determining element producing a different modulating frequency, and means to receive the transmitted carrier wave, the receiving means including filters by which particular modulating frequencies may be recognized, and indicating means by which the receipt of each particular modulating frequency is indicated.

2. A system as claimed in claim 1 comprising a jack connected to each frequency determining element, and a plug connected to the transmitter modulator by which the frequency determining element may be connected temporarily.

3. A system as claimed in claim 1 in which the transmitter is a VHF transmitter.

4. 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.