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05 - LabSat3 Record and Replay operations in detail

Replay operation

LabSat 3 uses SD card or HDD memory for storage and playback of GNSS data.  It is important to note that Class 10 or higher cards must be used to sustain the transfer speeds required.  Racelogic recommend SanDisk Extreme Class 10 cards for best performance.

 

The 1TB USB Hard Disk Drive (HDD) supplied contains a selection of pre-recorded scenarios from around the world.  These scenarios can easily be copied to the SD card for replay. The HDD supports either USB2.0 or USB3.0.  For optimum data transfer performance using a PC that supports USB3.0 for file transfer from HDD to SD card is recommended.

 

The RF OUT connector is a 50Ω output which can be connected directly to the antenna input of the GNSS receiver being tested.  The RF OUT connector of LabSat 3 is DC blocked internally so almost any device can be connected to this port. When a file is selected for replay, the LabSat will configure constellation frequencies and digital channels automatically before starting replay.  If a triple constellation file is selected for replay on a single channel LabSat, all three constellations will be displayed before replay allowing the user to select one.

 

During replay, pressing OK will show a live histogram of satellite levels detected by the internal GNSS receiver.  The internal receiver currently only supports GPS and GLONASS constellations.  This has no effect on the ability of LabSat 3 to record or replay BeiDou signals.  When displayed, the UP/DOWN keys switch between GPS and GLONASS monitor modes.  Please note that when switching between GPS and GLONASS display modes, the internal receiver will take some time to re-acquire satellite signal levels.  In the case of GLONASS signals, it may take over a minute to show the satellite signal information.

 

LabSat 3 comes with an internal 31dB attenuation capability.  To increase the attenuation press the up arrow, this will increase the attenuation by 1dB.  The down arrow will decrease the attenuation level.

 

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Record operation

LabSat 3 uses SD card and HDD memory for storage and playback of GNSS data.  It is important to note that Class 10 or higher cards must be used to sustain the transfer speeds required.  When recording two constellation types, the data rate is approximately 8.2MB (Mega Bytes) per second.  To ensure that data is collected without error, the card should be able to sustain 10MB per second. Spare cards and HDDs may be purchased from Racelogic.

 

It is important that cards are formatted as FAT32. LabSat 3 is able to format cards and HDDs in FAT32 with the optimum configuration for high speed recording.  When a card or HDD is formatted by LabSat 3, it will also carry out a performance test to determine whether or not the media can sustain the required bandwidth and inform the user if this is not the case.

 

For record capable systems, the LabSat will be supplied with a magnetic mounting GNSS antenna. The antenna is an active device with approximately 28dB of gain.  The LabSat provides a 2.85V DC bias for antenna power on the centre pin of the RF IN connector. It is also possible to use third party antennas providing they are compatible with the 2.85V bias.  If connecting LabSat to an antenna which requires a higher bias voltage (e.g. 12v), the antenna bias must be supplied by the user and an appropriate DC block (such as DCB from http://gpsnetworking.com/attenuators.asp) must be inserted at the LabSat 3 RF IN connector to avoid damage to the LabSat.

 

There are a number of GNSS systems currently in operation or in a test phase. These operate on 3 main frequency bands.

These are:-

 

Frequency Band Constellations
1575.42MHz GPS L1, Galileo E1, QZSS, SBAS
1602MHz GLONASS L1
1561.098 BeiDou B1

Depending on the model, LabSat 3 will have 1, 2 or 3 RF channels. This allows recording of 1, 2 or 3 frequency bands so, for example, a 2 constellation LabSat 3 may record the band containing GPS L1/Galileo E1 and the band containing GLONASS L1 simultaneously.  Recording of the desired constellations is configured in the CONSTELLATION menu.  In this menu, the user can tick up to three of the desired constellation groups (depending on version).  If only one constellation is ticked, then an additional option for 2bit will be available to allow 2bit quantized recording for the selected constellation.

 

Once the constellations are configured, exit the menu and press the REC button to begin recording. A new file will be created each time recording starts.  The file name used corresponds to the constellations selected.  For example, if GPS and GLONASS are selected for recording, the file created will be GPSGLO_nnn where nnn is a number that increments with each new recording.  Details of the LS3 file format are available on request from Racelogic.

 

During recording, pressing the OK button will switch the display to show satellite levels for either GPS or GLONASS satellites.  In this display mode, the up and down arrow keys will toggle between GPS or GLONASS constellations.  BeiDou constellation is not currently supported by the internal monitor but BeiDou B1 signals can still be recorded and replayed.

 

To maximize battery life during recording, LabSat 3 has a power save mode which is enabled by default I n the setup menu.  Power save mode recognizes when running from battery power and will dim the display backlight and power-down the internal GPS/GLONASS monitor after 30 seconds of user inactivity. 

 

If recording from passive antennas such as the Maxtenna M1516HCT-SMA GPS/GLONASS antenna, enabling the power-save mode will also provide the highest possible sensitivity by ensuring that unused modules within LabSat 3 are switched off.

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Last modified
12:39, 17 Jun 2015

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