GPS Receiver Calibration by BIPM Aimin Zhang National Institute of Metrology(NIM), China APMP/TCTF 2012 in Wellington, New Zealand

Calibration Procedure BIPMLab under calibration (1)Provide guidelines and the travelling receiver (3) Compute the total (internal + antenna) delay of the receiver and send the result to the lab (5) Modify the type B uncertainty in Circular T if needed (2)Get the travelling receiver and perform the measurements according to the BIPM Guidelines Send original data and report to BIPM (4) Get calibration result from BIPM and revise the receiver values for CGGTTS file

Guidelines and operational procedures using the travelling BIPM receiver 1. Description of the equipment travelling receiver: Z12T, PolaRx2, GTR50 2. General information Hardware connection and Data acquisition 3. Relating the internal reference to the laboratory reference 4. Measurements for differential calibration of total (internal + antenna) delay 5. Data report

Traveling receiver to NIM: GTR50 (BP0U)  Equipment supplied: - Dicom GTR50 (serial number ) - Antenna Novatel GPS-702 GG (serial number NAE ) - Antenna cable about 50m long (number C134)  Non-supplied necessary equipment: - Computer screen and keyboard

Traveling GTR50 (BP0U) hardware connection

Relating the internal reference to the laboratory reference  It should be carried out at the beginning and the end of the experiment  The delay between 1 PPS input and 1 PPS output is equivalent to the delay measured in set-up (2) minus the tare delay in set-up(1)  the delay of the receiver reference vs the 1PPS-in : For Septentrio PolaRx is the 1PPS-out, delayed by 8.7 ns. (1)tare measurement before and after operation(2)delay measurement during operation NIM receiver under calibration: Septentrio PolaRx2(IMPR)

Measurements for differential calibration of total (internal + antenna) delay  The two systems are set-up independently (2 antennas). The input frequency and the 1 PPS in for the two systems are derived from the same reference.  Four days to one week of measurements are taken with a 30s data interval and stored in daily Rinex files.

Data report  The information provided to BIPM: ① A figure describing the actual set-up with indication of all measured delays. ② Results of delay measurements. ③ Precise coordinates for the phase centers of the two antennas. ④ A log of events.  The data from the two receivers are to be provided in daily RINEX files.  The BIPM receiver data are stored on the traveling PC.

NIM report: PolarX2 set-up Phase micro stepper Total ant delay = Ant cable delay+Splitter delay+cable delay = = ns Clock cable delay = 22.4 ns (before operation) Clock cable delay = 23.3 ns (after operation) UTC(NIM) PPS Distribution f Distribution splitter XP = 22.4 ns XO = ns XC+XD = ns XP: From external reference to 1PPS in XO: From 1PPS in to internal reference XC, XD: Cables etc... from antenna to receiver XR: receiver internal delay; XS antenna delay

NIM report: BIPM GTR50 set-up Phase micro stepper Clock cable delay = 28.8 ns (before operation) Clock cable delay = 29.4 ns (after operation) UTC(NIM) PPS Distribution f Distribution XP = 28.8 ns XO = 0 XC+XD = ns REF DLY = 28.8 ns CAB DLY = ns

Results of differential calibration  Measurement period: , doy (23-29 December 2009) Delta (-XP-XO+XR1+XC+XD+XS1) (IMPR - BP0U) = 84.3 ns Delta (-XP-XO+XR2+XC+XD+XS2) (IMPR - BP0U) = 84.3 ns Therefore: IMPR: XR1+XS1 = ns IMPR: XR2+XS2 = ns

Uncertainty  The standard uncertainty on such a link calibration is taken to be 5 ns (1 σ).  NIM calibration result was introduced in circular T 265

Thank you for your attention!