09 - LabSat 2 Recording GNSS Data
NB: Applicable to RLLSC02-GNL1 and RLLSR02-GNL1 LabSat 2 Models Only
The GNSS antenna supplied with the LabSat 2 is a 3 V active antenna with 28 dB gain. For the best possible signal quality, it is important to maintain a good RF connection between the antenna and the LabSat. Before fixing the antenna to the LabSat, ensure that there are no dust particles in either connector. Replacement antennas are available by contacting your LabSat distributor.
The antenna is a magnetic mounting type for quick and simple mounting to the vehicle roof. For optimum GNSS signal reception, make sure that the antenna is fitted to the highest point of the vehicle away from any obstructions that may block satellite reception. The GNSS antenna works best with a metal ground plane underneath (a metallic vehicle roof is perfect for this).
Please also note that when using any GNSS equipment, a clear view of the sky, without physical obscuration, is important. Objects in the surrounding area such as tall buildings or trees can block the GNSS signal causing a reduction in the number of satellites being tracked, or introducing reflected signals that can decrease the accuracy of the system. Note that clouds and other atmospheric conditions do not affect the LabSat’s performance.
GNSS antennae require a ground plane to operate correctly. This helps to reduce unwanted reflections of the GNSS signals caused by nearby objects, and usually the metal roof of a vehicle performs this function. However, if a test requires an antenna to be placed either off the vehicle, or on a vehicle that does not have a metallic roof, a special ground plane antenna must be used. This has an internal ground plane and can operate perfectly without the need for mounting on a metal surface. Ground plane antennas are available from your LabSat distributor.
The LabSat 2 is set up according to the diagram below.
- Connect the Active GNSS antenna to the RF IN port of the LabSat 2.
- Connect the high speed USB cable to the computer on which the Scenario data file is to be recorded. It is possible to connect an external USB drive to the computer and stream the recorded file directly onto this drive.
- Connect power to the LabSat 2.
- Start the LabSat software.
Before recording Scenario data it is important to observe certain criteria, failure to follow these precautions may result in satellite data dropouts or corrupt data contained within the recorded file.
Very Important: Running Background Applications if Logging to Computer
The LabSat 2 has a two second USB buffer, but due to the exceptionally high data rates and processing power utilised by the LabSat 2 USB bus when recording GNSS data, it is important to have no other applications running on the computer and not to start any other applications whilst the LabSat 2 is recording data. Also make sure you do not start to move windows around, or do anything which takes processing power away from the LabSat 2 application, as Windows can occasionally stall for more than 2 seconds when launching/running other applications. Even though you may have multiple USB ports on your computer, in most cases they all share the same bus. Therefore try to limit any activity using additional USB devices.
Recording Data to an External Drive:
It is recommended that any external drive used to record scenarios is formatted in the NTFS format. The FAT32 format has a file size limit of 4 GB, which is equivalent to about 34 minutes of recording. The USB drives supplied with the LabSat 2 are pre-formatted using the NTFS file format.
- Once the LabSat software is running, LabSat 2 is now ready to record data.
- Click the Browse Button. The user will be prompted to enter the filename and choose the location of the recorded file.
- Click the Record Button. The REC Light on the front panel of LabSat 2 will start to flash, indicating that LabSat 2 is recording GNSS RF data.
- As the LabSat 2 begins to record data the Duration timer will indicate the length of scenario recorded and file size will begin to increase.
- During Record, the Buffer display may be selected, to show that the buffer is not becoming overloaded. The illuminated bar graph indicates buffer level and there is also a moving line graph showing buffer level over time. The LED display on the LabSat 2 front panel also indicates the status of the buffer.
- The Advanced Recording Control allows users to pre-select either a fixed recording time or a fixed recording file size. The default option is continuous recording. In the example, below, a fixed scenario time of 2 minutes 10 seconds has been selected. The scenario record time may also be limited by selecting a maximum file size, for the recorded scenario. The Description box allows for a detailed description of the recording to be entered.
- The channel mode selector determines which channels are used and the quantisation level.
- GNSS Monitor displays the NMEA Output from the internal GPS Receiver within LabSat 2. Connect the GNSS Monitor Port (USB Mini ‘B’) to a spare USB Port on your PC. The GPS data being recorded is simultaneously displayed by LabSat 2’s internal GPS receiver engine, on the GNSS Monitor display, as shown below.
- Click Stop, to halt recording GNSS RF data.
Note: Satellite Lock
There is no ‘acquisition time’ as such when recording data with the LabSat 2 as it is recording the complete RF signal rather than tracking individual satellites. However, when recording data, we recommend that you allow around 5 - 10 minutes of stationary recording in an open location with good unrestricted visibility of the entire sky before moving off. In this way any GNSS engine receiving the LabSat scenario data will have plenty of time to lock onto satellites and begin storing almanac data.
Note: LabSat 2 Data Rate
LabSat 2 records RF data over high speed USB at a data rate in excess of 8 MB/sec, this means the data files created by LabSat 2 become large very quickly. It is important to ensure that there is sufficient space on the computer or USB hard drive where the recorded data file is to be stored.