The HD CSAC GPSDO is based on the Jackson Labs Technologies, Inc. CSAC (Chip Scale Atomic Clock) GPSDO platform, but optimizes size, weight, and power (SWAP) by removing some of the generic features of the CSAC GPSDO. The HD CSAC was designed for mobile applications such as man-pack, airborne, and vehicle applications. The HD CSAC GPSDO provides an RS-232 serial port for command and control, and operates from a +12V power supply. It includes CMOS and LVDS 10MHz outputs, and an LVDS 1PPS output. It is function compatible to the FireFly-II board, and shares the same IO connector while drastically reducing power consumption and improving performance, especially during GPS holdover. The HD CSAC GPSDO supports a mobile-mode GPS receiver with 50 channels and SBAS (WAAS/EGNOS/MSAS) support, and better than -160dBm tracking capability. The HD CSAC supports industry-standard NMEA output sentences, and an SCPI control and command interface. The board is available in standard temperature versions, as well as extended temperature versions with -10C to +70C temperature range.