How To log CGGTTS data with the PolaRx4TR receiver 1. Introduction CGGTTS (CCTF Group on GNSS Time Transfer Standards) is a standard defining a data format which allows accurate transfer of time and frequency using GNSS systems. Using a PolaRx4TR receiver, users are able generate CGGTTS files automatically using the GUI interface tool RxControl. This short guide is designed to help users understand how the CGGTTS files are generated and to setup both the receiver and RxControl correctly. You can obtain further information from our Support team at Septentrio by emailing: [email protected]. 2. How do I log CGGTTS files? RxControl generates CGGTTS files from RINEX data so RINEX files will be created as an intermediate product when generating CGGTTS. You can elect to save these RINEX files as well. Before starting logging, you should first ensure that the receiver is properly configured otherwise CGGTTS files may not be created. 1.1 Receiver setup with EXT REF and PPS IN signals The PolaRx4TR receiver should to be correctly set-up using an external time reference. A 10 MHz frequency reference should be connected to the REF-IN connector on the back panel of the receiver before the receiver is powered. The internal clock of the receiver will then be bypassed and the external oscillator used instead. A PPS-IN signal should also be connected before the receiver is powered in order to synchronise the receiver with the phase of the external timing reference. The receiver is synchronised using the PPS-IN only once at start-up whereas the REF-IN signal is used continuously. The behaviour of the clock bias with and without the REF IN and PPS IN is shown schematically in Figure 1. 1 of 9 Figure 1: schematics of clock bias plots When the 10 MHz and PPS IN signals are properly connected and recognised by the receiver then EXT_REF and PPS_IN will be displayed in the lower right corner of the main window of RxControl as indicated in Figure 2. If these signals are connected to the receiver but EXT_REF and PPS_IN do not appear then there may be a problem with the cabling or signal levels. F i Figure 2: RxControl showing the external 10 MHz and PPS IN signals are connected. 2 of 9 1.2 Logging of CGGTTS data using RxControl The receiver can be configured to log CGGTTS data using RxControl. On the main window select ‘Logging’ then ‘RxControl Logging’. This will open up RxControl Logger where all the necessary settings can be made. In the ‘SBF’ tab, you should select ‘Rinex’ as shown. This will automatically select all the SBF blocks necessary for RINEX and thus CGGTTS generation. In the ‘File Naming’ tab, ‘IGS 24 hours’ should be selected. Figure 3: Selecting to log RINEX data in 24hr IGS named files 3 of 9 In the ‘Post Processing’ tab shown in Figure 4, you can define what you want to happen to the data. By first clicking on ‘Add’ as highlighted below, you can then select ‘CGGTTS Conversion’ from the drop-down list. Figure 4: Defining a new post-processing action. In one of the following windows (see Figure 5), you will be asked to input certain delay values and Laboratory and Reference names that will appear in the CGGTTS data file header. The delays are setup specific and are usually determined by comparison with a calibrated reference receiver from BIPM. Some additional information on the various delay values that need to be entered is below: CGGTTS parameter Int Delay P1 BIPM notation XR1+XS1 Int Delay P2 XR2+XS2 Ant Cab Delay XC+XD Clock Cab Delay XP+XO Comments Combined receiver and antenna delays at the GPS L1 frequency (excluding cables). To be calibrated using BIPM (1) procedure. Combined receiver and antenna delays at the GPS L2 frequency (excluding cables). To be calibrated using BIPM (1) procedure. Total cable and splitter delays from the antenna connector to the RF IN connector of the PolaRx4. XP is the delay in the cable from the external PPS reference to the PPS IN connector of the PolaRx4TR. XO is the receiver internal delay from the PPS IN connector to the measurement latching. It can be measured following the instructions in section 1.1.5 of the PolaRx4 Product Family Hardware Manual. (1) Additional information and a sample calibration sheet from BIPM can be found here: ftp://tai.bipm.org/TFG/CALIB_GEO/CalibGeo_sample.pdf 4 of 9 Figure 5: Inserting parameters specific to CGGTTS data files. It is also important that the ‘True Antenna Position’ is correct. The correct value can be inserted by pressing on the ‘Info’ button as highlighted in Figure 5. This will open the box shown in Figure 6 below where, by following; File > Preferences the correct position can be entered. 5 of 9 Figure 6: Inserting the correct antenna position You can also select where you want the resulting CGGTTS files to be put. The files can be stored either locally or FTP’ed to a remote PC as Figure 7 shows. The default location is in the same folder as the SBF files. Figure 7: Selecting the destination of the logged file. 6 of 9 The newly defined process can then named and described as shown in Figure 8. Figure 8: Naming and describing the CGGTTS process Finally, you should select to use the defined CGGTTS process by ticking the ‘Enable’ box next to the process as shown in Figure 9. Figure 9: Selecting to use the newly defined process 7 of 9 1.3 Additional Information  Certain values in CGGTTS files are averaged over 13 minute measurement periods and, as the last period extends into day 2, this means that a CGGTTS file for day 1 will only appear at the end of day 2.  The CGGTTS conversion uses an application created by Pascale Defraigne from the Royal Observatory in Belgium and is based on the IGS/BIPM Time transfer procedures. Below are some links with helpful documents about CGGTTS: o http://tycho.usno.navy.mil/cggtts.html o http://www.bipm.fr/static/gpst/ o http://www.bipm.org/wg/AllowedDocuments.jsp?wg=CGGTTS  If you have RINEX files already then it is still possible to generate CGGTTS data offline. This can be done by running rin2cgg.exe (normally found in C:\Program Files\Septentrio\RxTools\bin) as a command line tool. What you will need to do to create CGGTTS data for day#1 is; 1. Have 24 hr RINEX files for day#1 and day#2. 2. Edit files ‘inputFile.dat’ and ‘paramCGGTTS.dat’. These two files should be the same folder where rin2cgg.exe is executed. Samples of these two files can provided by the support department. 3. In the inputFile.dat file, the four input RINEX file names and pathways should be correct as well as the output filename that you want for the CGGTTS file. 4. The paramCGGTTS.dat file contains the antenna position and the various receiver timing calibration parameters which should be correct. 5. The day for which you want the CGGTTS file is expressed as the ‘MODIFIED_JULIAN_DAY’ and is the day of the first RINEX file. A Julian day converter can be found here; http://www.csgnetwork.com/julianmodifdateconv.html 6. Run rin2cgg.exe in the command line as shown below. 8 of 9 References: - RxControl Manual - Calibration of dual frequency GPS receivers for TAI - G. Petit, P. Defraigne, B. Warrington, and P. Uhrich, For more information: Septentrio Support Tel +32 16 300 800 Fax +32 16 221 640 Email: [email protected] www.septentrio.com How to CGGTTS Setup v2.0 (PolaRx4 TR), April 2012 9 of 9