GPS Software Radio. Direct RF Sampling Research

The future satellite positioning navigation systems will provide civil signals on multiple frequencies, similar to that currently available only for the military pie. The multiple distinct frequencies will provide many advantages to users of the navigation systems. This report presents the development of a direct RF sampling front end design well suited for multiple frequency satellite navigation receiver design. No frequency down conversion is necessary, rather the particular frequency bands of interest are intentionally aliased using a wide band Maxim 104 analog-to-digital converter (ADC). The resulting samples are passed, via a buffering FPGA design, to the memory space of a host PC for storage as well as eventually processing of the multiple frequency transmission. This paper describes the design of the front-end, validates its concept with collected data. The system designed was demonstrated at Wright Labs and the developed hardware configuration/software was transferred was their use.