Inexpensive Radar-Responding Relocation Device for Drifting Oceanographic Instruments

摘要

The instrument described was designed to provide sufficient data to relocate a floating object at sea. It provides a line of bearing to the object from the tracking ship. Cost and power consumption were the major driving concerns. There is a minimum of microwave circuitry. The package is reproducible for under $2,000. Our system, which requires no special, wideband receivers 'Answers' 3-cm ship radar with a VHF signal. This signal is received on the ships VHF radiotelephone and correlated to the target bearing by the observer. A short (one-quarter second) tone is heard whenever the rotating radar search beam sweeps over the drifting buoy. The observer, while watching the PPI scope display of the ships radar, observes the bearing cursor at the moment that he hears the tone. Bearings to +/-2 to 3 degrees are readily obtainable. The most critical part of the system, as well as the most expensive (almost $300) is the X-Band antenna system. This component is used on Motorola's own radar transponders. It is an array of slot dipoles tuned to the 3 cm marine radar band. The assembly is weatherproof and used as is in the surface unit. It provides the function of antenna and tuned 'front end' for the responder. A low-noise detector diode is mounted directly to the antenna assembly and connected by coax to the 2N5031 preamplifier stage.