We present the design and implementation of a highly portable multi-antenna datalogging system which can log several minutes of multi-channel raw GPS L1 baseband. In addition, our design interleaves two serial data streams with the baseband data, allowing, e.g., inertial data to remain synchronized with the data stream. The system is FPGA-based and uses two CompactFlash cards for storage. The data is extracted by imaging the CompactFlash cards onto a PC and recovering synchronization codes interleaved with the baseband data. The resulting system is useful for multi(and single-) antenna receiver development, as it allows for simple data collection. The data files Figure 1. Multi-channel GPS L1 data collection system can then be used as inputs to software receivers for algorithm development, testing, and quantitative comparisons. Because the digital logging section is cleanly separated from the RF front-end section, it is possible to substitute any manner of RF front-end (e.g. Galileo) in place of our GPS L1 section, so long as the total data rate stays within the 250 megabit/sec capacity of the logging section.