Dual frequency anti-theft system
CA 1190970 A · Owner: Deterrent Technology Corporation · Inventors: Williams, Harold B.
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
An article surveillance system employs a label or tag containing a non linear impedance element such as a, semiconductor diode, connected to a metal antenna loop configured to pick up two distinct radio frequency transmissions displaced on either side of a selected center frequency. The non-linear impedance element connects opposing sides of a closed loop section at one end of the antenna to form a tuned tank circuit having a resonant frequency twice that of the selected center frequency. A first transmitter generates a tone modulated radio frequency displaced on one side of the center frequency and a second transmitter generates a continuous wave radio frequency displaced from the center …
Read the whole patent
Listed from its CIPO record in Patent Yard's archive of Canadian patents past their term. Its claims, description and drawings are in the CIPO record and on Google Patents, and the Claude kit works from them.
Why it's free to use
- Granted July 23, 1985. A Canadian patent filed before October 1, 1989 lasted 17 years from grant, so its term ended July 23, 2002.
- We check Canadian rights only. A patent in its family in another country could still be in force: check its family on Google Patents.
Timeline
Timeline From CIPO dates
Sources & verification
Official CIPO records
Everything on this page comes from the CIPO record linked above. Contains information licensed under the Open Government Licence – Canada.