2016-06-24 Sawtooth corrections
The effectiveness of the 1 pps sawtooth correction varies between GNSS receiver models. The sawtooth is typically designed to have a short period so that it can be quickly averaged out. In particular, at the averaging time of 780 s stipulated for a CGGTTS track, the smoothing afforded by the sawtooth correction is no longer distinguishable.
In the measurements below, the receiver's 1 pps has been measured against a caesium beam standard, for which TDEV is less than 0.5 ns for τ less than 10 000 s, and then sawtooth-corrected using the correction given by the receiver. The receivers are a Javad HE_GD, Trimble Resolution T and NVS NV08C. The Javad receiver has the most effective sawtooth correction.
2016-06-20 Breadboarding the prototype
A prototype system is currently under test. It comprises a Beaglebone Black, NVS NV08C GNSS receiver, Jackson Labs LTE Lite GPSDO, Opal Kelly XEM6001 FPGA board and an SSD for data storage. All device connectivity is via USB. In the production version, all OEM boards will plug into a common motherboard.