The Naval Research Laboratory (NRL), as part of the Global Positioning System (GPS) Center of Expertise (COE) test program, performs absolute calibration of GPS receivers for time transfer. NRL did a simulation of this calibration method to verify the procedure. The simulation focused on the effects of filters, external to receiver, on receiver calibration. Two areas were investigated in this simulation. Will changes in the data from two different types of receivers track if the bandwidth of the signal source to both receivers change? If a filter is added between the antenna and a receiver, can this combination be calibrated in parts or must this combination be calibrated together? CALIBRATION METHOD The calibration of a GPS receiver is accomplished with a GPS signal simulator. The simulator generates two signals: a simulated GPS antenna signal and a one pulse per second reference . The receiver is connected to the simulated antenna signal and the time determined by the receiver is compared with the time of the simulator reference (Figure 1). An additional step of calibrating the simulator is also necessary, which is done by connecting a high-speed digital scope to both outputs of the signal simulator
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