The instruments have a precision clock calibrated against a GPS generated time-code. The GPS antenna has to be located outside, usually on an exterior wall, with a clear view of most of the sky.The antenna cable is a coax cable supplied by the seismograph vendor and has a length of 80 feet. The antenna cable length is often a critical factor when locating the seismograph at a particular facility. The cable will need to be routed from the sensor/digitizer to the outside antenna, sometimes going through a wall.
Currently, the GPS is used only for accurate time-stamping of data.
The photograph below is of a typical GPS antenna and cable system
Updated August 7, 2002
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