Abstract: A wireless, real time video system provides a low power video transmitter wherein the base band video signal generated by the video camera directly modulates a radio frequency carrier signal to produce a very narrow band transmitter signal that is transmitted through a circularly polarized patch radiating antenna to a receiving antenna at a remote receiver site. The transmitted signal is picked up by the receiver antenna to be passed through a narrow band preselector filter to a low noise amplifier. The amplified signal is then applied to a mixer along with a fixed local oscillator frequency that is demodulated to reconstruct the original base band video signal for use in operating a video monitor or recorder connected by hard wired cable to the receiver unit.

Abstract: 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 frequency on the other side. Both transmitter signals are fed separately to respective radiating antennae located adjacent to a surveillance area. The antennae are chosen to produce circularly polarized transmission of both frequencies within the surveillance area.