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OXTS GPS-Base, User Manual

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OXTS GPS-Base User Manual Download Page 30

 

 

30 

Oxford Technical Solutions

 

Differential correction format details 

There are different messages within each differential correction type and these can lead 
to incompatibilities between different GPS products, even though they claim to support 
the family of differential corrections. For example the RT2004 only supports its RTK 
Integer positioning mode when using the RTCA2 format of the GPS-Base. 

Table 10, Table 11 and Table 12 list the messages output by the GPS-Base for each 
correction type. These are the corrections required for OxTS products. When using the 
GPS-Base with other products check that the other GPS receiver supports these 
messages and can operate in the desired mode using them. 

Table 10. RTCA messages output by GPS-Base 

Message  Period 

Purpose 

RTCAREF 

10s 

Information about the base-station, for example the position of the base-station. 

RTCA1 

1s 

Differential or pseudo-range corrections. These are suitable for the differential 
positioning mode. 

RTCAOBS 1s Carrier-phase 

corrections. 

These are suitable for the RTK Float and RTK 

Integer positioning modes using GPS only. GLONASS is not supported, so the 
RT2004 does not work optimally with this message. 

 

Table 11. RTCA2 messages output by GPS-Base 

Message 

Period 

Purpose 

RTCAREF 

10s 

Information about the base-station, for example the position of the base-
station. 

RTCA1 

1s 

Differential or pseudo-range corrections. These are suitable for the differential 
positioning mode. 

RTCAOBS2 

1s 

Carrier-phase corrections. These are suitable for the RTK Float and RTK 
Integer positioning modes using GPS and GLONASS. This format is required 
so that the RT2004 will work optimally. The older RT3000 products (serial 
numbers below about 150) cannot use this new message. 

 

Summary of Contents for GPS-Base

Page 1: ...Confidently Accurately GPS Base GPS Base Station GPS Base User Manual ...

Page 2: ...present a commitment on the part of Oxford Technical Solutions Limited This publication supersedes and replaces all information previously supplied Oxford Technical Solutions Limited products are not authorised for use as critical components in life support devices or systems without express written approval of Oxford Technical Solutions Limited All brand names are trademarks of their respective h...

Page 3: ... notices 13 Regulatory testing standards 13 Operation and configuration 14 Choosing a suitable location 14 Connections 14 GPS Base software 16 Choosing the connection 16 Choose port 17 Scan ports 17 Remember this port selection 18 Configuring the GPS Base 18 Average position 19 Restore position from file 19 Enter antenna position 20 Leave unchanged 20 Advanced 20 Status page 21 Status 22 ...

Page 4: ...titude 23 Base Station ID 23 Logging Novatel binary 23 Logging RTCM V3 24 Save position to file 24 Start logging 25 LED status 26 SATEL radio status 26 Freewave radio status 26 Discussion on repeatability 28 Differential correction format details 30 Revision history 32 ...

Page 5: ...d L1 GLONASS corrections suitable for 20cm positioning Some RT products can achieve 2cm accuracy using this model GPS Base 2 L1 L2 GPS corrections suitable for 2cm positioning GPS Base 2G L1 L2 GPS and L1 L2 GLONASS corrections suitable for 2cm positioning The GPS Base is available with several different radio options Different radios are required for license free operation in different countries ...

Page 6: ...s from each satellite vary slowly and predictably The GPS in the car uses a model to predict the error from each satellite It can update its model when the radio link transmits new data It is not necessary for the GPS in the car to wait until the radio has transmitted the correction before it outputs its latest value Correction types The GPS Base can transmit differential corrections in different ...

Page 7: ... different formats is given at the end of the manual in the section called Differential correction format details File logging The GPS Base software can log data on to the hard disk of the PC Files can be logged in Novatel binary format and in RTCM V3 format Features The GPS Base is a self contained unit that includes The Base Station GPS receiver External Radio Modem GPS Antenna 15m Cable and Tri...

Page 8: ...bands available for many European countries Radio will typically cover 8 bands with 25 kHz channel spacing SATEL 869 MHz band up to 500 mW typically 2 km License free across most of European Union Freewave 900 MHz band up to 1 W typically 10 km License free in USA Brazil Canada Futaba 2 4GHz band 10mW typically more than 1km License free in Japan ...

Page 9: ...S Base Oxford Technical Solutions cannot be held responsible for using this equipment illegally without the correct radio license Table 4 Summary of the GPS Base components with SATEL radio Qty Description 1 GPS Base Unit 1 GPS C006 15m GPS Antenna Cable 1 GPS 702 GG GPS Antenna 2 SATEL Satelline 3ASd Radio Modem 2 Radio Modem Aerial Antenna with 3m cable and Magnetic Mount 1 Tripod 1 Power cable ...

Page 10: ...ntenna cable 1 GPS 702 GG GPS antenna 2 Freewave FGR 115RC 900 MHz radio 2 14C0044B Freewave radio cable 1 Car antenna short with 20ft cable 1 Base station antenna long with 20ft cable 1 Lightweight tripod 1 Power cable 1 Radio modem cable 1 PC USB cable 1 GPS Base user manual 1 GPS Base quick guide Figure 2 GPS Base components with SATEL radios ...

Page 11: ...it is shown in Table 6 below Table 6 Technical specification except radio modem Parameter Specification Power 6 18 V DC 2 W Operating temperature 40 C to 75 C Environment Dry environments Relative humidity 95 non condensing Corrections RTCA Differential L1 L2 RTCA2 RTCM V3 Frequency 1 Hz Format RS232 ...

Page 12: ... repair at an authorised location only Determination of replacement or repair will be made by Oxford Technical Solutions Limited personnel or by personnel expressly authorised by Oxford Technical Solutions Limited for this purpose In no event will Oxford Technical Solutions Limited be liable for any indirect incidental special or consequential damages whether through tort contract or otherwise Thi...

Page 13: ...n accordance with the instructions may cause harmful interference to radio communications However there is no guarantee that interference will not occur in a particular installation If this equipment does cause harmful interference to radio or television reception which can be determined by turning the equipment off and on the user is encouraged to try to correct the interference by one or more of...

Page 14: ... should not be left in the rain or other wet conditions Figure 3 GPS Base location away from buildings trees and reflective objects Connections Connect the GPS antenna to the tripod or to a secure pole The mounting should ensure that the antenna does not move including in wind or gusts such as when a car drives past Connect the GPS antenna cable to the GPS antenna and to the GPS antenna input on t...

Page 15: ... damage the GPS antenna Locate the radio modem aerial at least 2m away from the GPS antenna Clip the radio modem aerial on a metal object such as the roof of a car Connect the radio modem aerial to the radio aerial connector on the GPS Base unit OxTS has alternative aerials that are suitable for attaching to buildings and do not require a ground plane under the aerial Figure 4 GPS Base connections...

Page 16: ... after power is removed and restored e Set the base station identifier in to the GPS Base f Change the format of the corrections g Monitor the status of the GPS Base h Save differential correction data to disk The GPS Base software is organised as a wizard that will guide you through the operation of the GPS Base Choosing the connection Figure 5 shows the software when it is first run The left han...

Page 17: ...M ports for the GPS Base COM5 COM6 and COM7 Any of these can be used If these ports are taken by other software drivers then other ports will be used and it will be necessary to search until the correct port is found The GPS Base automatically scans all the available ports on start up and only lists the ports where a valid GPS Base has been detected Scan ports If the GPS Base was not connected whe...

Page 18: ...that has been saved it can be restored from the GPS Base it can be entered by the user or the GPS Base can average its position for a period of time to find an approximate location for the antenna There is some discussion at the end of the manual describing the benefits of each technique In general it is sufficient to average for 3 minutes For repeatable work save the averaged location and then re...

Page 19: ...rate to 2cm compared to other data obtained during this average If you re average you will end up in a different location and the data from the new location will not overlay the old location Use the Save Restore features so that future data will overlay the current data Restore position from file If you have saved the location of the GPS antenna to a file then you can restore that file using this ...

Page 20: ...ed in EGM96 not WGS 84 Leave unchanged Use this option if the GPS Base already knows its location and you do not want to change it If the GPS Base has a location stored internally or a location has already been acquired during the session this option will be selected automatically Advanced Using the Advanced Settings the correction type and the Base Station ID can be set This is an identifier that...

Page 21: ...s is available in the section called Differential correction format details By default the GPS Base will transmit OxTS as the Base Station Identifier Status page The Status page is used to monitor the GPS Base The GPS Base does not need the PC software to be running continuously once the GPS Base is configured then the PC can be disconnected Figure 8 shows the Status Page ...

Page 22: ...22 Oxford Technical Solutions Figure 8 GPS Base status page Status The status parameter shows the status of the GPS Base and the software Valid values for this parameter are listed in Table 7 ...

Page 23: ...cate and establish the mode of the GPS Base This mode should not last long Integrity Warning This occurs when the GPS receiver disagrees with the position that is being used Check that the antenna location corresponds to the position that has been entered or that the file used to save the GPS antenna location is correct Error There is some error It is probably best to restart the software and the ...

Page 24: ...ntial correction format When using this feature it is necessary to replace the GPS antenna in exactly the same position each time Only one antenna location can be stored on the GPS Base if a new location is stored it will overwrite the old one To find out which antenna location is stored in the GPS Base it must be connected to a computer and the software must be used If there is a location stored ...

Page 25: ...this option to start logging the raw GPS measurements from the GPS Base Once started the Start Logging button will become Stop Logging which will stop the logging of the raw GPS measurements when pressed While logging it is not possible to change page or quit ...

Page 26: ...e as shown in Table 8 Table 8 SATEL radio LED states and meanings LEDS Description RTS CTS TD RD CD Off Red Off Off Off Idle Off Red Red Off Red Transmitting a packet Off Red Off Off Orange Noise or other transmission on this frequency Off Red Off Green Green Receiving a packet Freewave radio status This section only applies to the Freewave radio option When operating the radio modems it is sensib...

Page 27: ... Green Green Green With the Freewave modems if the CD LED is red then the radio has not detected any other radios and it will not transmit or receive from them This can be seen on both the base and the mobile units since the Freewave radios use their bi directional communication to form a more secure link It can be difficult on the mobile unit to know if data is being received since only a transmi...

Page 28: ...e base station antenna is moved then the remote GPS receivers move too It is important to put the GPS antenna in a location where it cannot move or be moved See Figure 9 2 The base station has to measure its own position If the base station gets this position wrong then the remote GPS receivers will also be wrong They will be correct relative to the base station but they will have the same error o...

Page 29: ...rrors that all GPS receivers have and can only average its position to about 1 8m CEP If the user is prepared to wait a long time typically more than 24 hours then GPS is able to improve the accuracy of the base station antenna so it is accurate to 2cm or better However since the timescale for this is long it is not usually practical except for permanent installations Even when you have a permanen...

Page 30: ...Purpose RTCAREF 10s Information about the base station for example the position of the base station RTCA1 1s Differential or pseudo range corrections These are suitable for the differential positioning mode RTCAOBS 1s Carrier phase corrections These are suitable for the RTK Float and RTK Integer positioning modes using GPS only GLONASS is not supported so the RT2004 does not work optimally with th...

Page 31: ...e Period Purpose RTCM 1003 1s GPS differential corrections including carrier phase and pseudo range corrections RTCM 1006 5s Base station parameters information RTCM 1007 10s Antenna information RTCM 1011 1s GLONASS differential corrections including carrier phase and pseudo range corrections ...

Page 32: ... 090917 Added Advanced Settings for Base Station ID Added GLONASS options 100812 Added RTCM V3 logging RTCA2 and RTCM V3 correction outputs Changed to new radio modem cable 120111 Updated images and drawings to match new enclosure and connectors Added compatibility with RT2002 and RT2004 131025 Update image showing connections minor formatting and new products ...

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