A Codeless Ionospheric Calibrator for Time Transfer Applications

D. Davis, H. Weiss, H. Vidmar

Abstract:	With solar activity near maximum, the single largest error in the use of GPS for "common view" time transfer is correction for ionospheric delay. This paper describes the hardware and software development of a "codeless" ionospheric calibration receiver that recovers the P code clock on L1 and L2 and uses the phase difference to compute the L1 ionospheric delay. Major features of the hardware include dual-volute antennas on a choke-ring ground plane, very low-noise front end, and alternate L1--L2 phase sampling through a common IF channel. S/N of the recovered P code clocks is typically positive by several decibels in a 100 Hz bandwidth. Signals are processed as 8 bit data, with all satellites in view individually (and simultaneously) tracked in real time to recover the ionospheric delay values. All processing is with an internal 8 bit CMOS microprocessor. The normal mode of operation of the ionospheric calibration receiver is in parallel with a GPS C/A time transfer receiver, with the measured ionospheric data automatically replacing the modeled ionospheric data transmitted by the SV, In this way, the ionospheric calibrator operation is transparent to the time-transfer user. Data will show that the performance of the ionospheric calibrator is 1-4 ns for 15 s averages, with the ultimate limitation being multi path.
Published in:	Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989) September 27 - 29, 1989 The Broadmoor Hotel Colorado Spring, CO
Pages:	451 - 459
Cite this article:	Davis, D., Weiss, H., Vidmar, H., "A Codeless Ionospheric Calibrator for Time Transfer Applications," Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989), Colorado Spring, CO, September 1989, pp. 451-459.
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