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RFI Shielding Limited RFI Shielding Limited
 
RFI Shielding Limited
RFI Shielding Limited RFI Shielding Limited
RFI Shielding Limited RFI Shielding Limited
RFI Shielding News

Shielding stops jamming of GPS signals

The new Raytheon Raystar 112 LP receiver offers a new dimension in antenna design. Not only does it offer outstanding GPS accuracy, it also has a remarkable low profile, mount anywhere case. RFI Shielding Limited

Such is the flexibility of Raytheon's new GPS, it can be installed on the rail, on a pole, or even directly on the deck of a boat. This robust, fully waterproof unit will withstand whatever the marine environment will throw at it, including heavy feet!

The Raystar 112 LP provides accurate GPS navigation data for Raytheon `autopilot', `chartplotter' or radar systems. It's 12-channel design enables it to track up to 12 channels simultaneously. Coupled with automatic, microprocessor controlled signal acquisition, fast Time to First fix, one second update rate and extensive choice of geodetic data, the Raystar 112 LP offers the perfect position fix for Raytheon on board systems.

The Raystar 112 LP GPS sensor is a very compact design. The mechanical arrangement forced the GPS patch antenna to be mounted on a ground plane 5mm above the circuit board. The connection to the antenna is via a turned pin, directly soldered to the PCB.

On evaluation of the first prototype units it was quickly apparent that the GPS signal at 1.57542 GHz was being jammed by noise generated from the microprocessor incident on the antenna pin. In addition there was a large impedance mismatch between the antenna and the RF input due to the pin not being a 50Omega element. This resulted in a significant loss of the signal. Initially a coaxial cable connection was considered, however this was rejected due to difficulty in connecting the short length required to the PCB.

The answer lay in a small, extruded gasket of RFI's Supershield S400. This conductive gasket is fitted along with a suitable insulator around the pin to form a coaxial connection. As the antenna is fitted to the PCB the gasket is compressed slightly providing a vibration tolerant connection. The coaxial connection formed is dimensioned so as to provide a 50Omega characteristic impedance thus reducing signal loss into the RF input. The shield also protected against the RF signal against locally produced jamming noise. This approach provided a 25% improvement in signal to noise ratio, which ultimately results in better signal acquisition and navigational accuracy.

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RFI Shielding Limited

Courtesy of Tony Adams
Raytheon Marine Europe Ltd


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