Task Sheet - Single Base and VRS Rebroadcast

September 2005
Using a Trimble® SNB900 to reduce the need for GPS
base stations.
Remote Base Station and Virtual Reference Station Rebroadcast
Learning Objectives
Learn to configure the SNB900 for use with Remote Base Station (RBS) or Trimble Virtual
Reference Station (VRS)
Understand the different communication options and the features and benefits of each configuration.
Name the equipment used for different configurations
Name the 3 Configurations of the base stations that can be used.
Understand the base authentication methods
Understand the status information displayed by the SNB900
Basic Troubleshooting
VRS and 2 Way data
Trimble Construction Division, 5475 Kellenburger Road, Dayton, OH 45424, USA
© 2005, Trimble Navigation Limited. All rights reserved. Trimble and the Globe & Triangle logo are trademarks of Trimble
Navigation Limited, registered in the United States Patent and Trademark Office and in other countries. All other trademarks are the
property of their respective owners. PN 022482-270 (09/05)
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Configuration of the SNB900 using WinFlash
1) On the computer, run the WinFlash utility. The Device Configuration dialog appears,
1. Select SNB900
2. Select the appropriate computer serial port (COM port).
3. Select SNB900 and then click Next. The Operation Selection dialog appears:
4. Select the Configure Modem option and then click Next. The Settings Review dialog appears.
Note: The SNB900 must be configured, via the front panel, to be in Easy IP mode before select Configure
Modem. Rebroadcast is only available when the base station operates in Easy IP mode. Easy IP base
broadcast is compatible with V1.44 or higher.
The SNB900 should be configured as a BASE station
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2) The Configure Modem Operation dialog will appear.
3) Select the Dial Out radio
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4) In the Modem Init Strings box,
initialization strings for circuit
switched operation with your
1. The initialization strings
used for circuit switched
operation with SCS900
should be used here.
2. For dial out operation init
strings are most often not
Nextel cell phones often
need an Init String of
If you are unsure what strings should
be entered, contact the modem
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Note: The Trimble SNB900 does not directly support internet based connections, an Airlink Raven or
Redwing modem is used for cellular connections. A Lantronix UDS-10 is used for Wired connections
5) In the Phone Numbers box, enter
the phone number that the
modem should dial.
1. The SNB900 can dial up to 4
numbers in a round robin
operation. Which is makes
operation with a computer
with multiple modems easy.
If using an internet modem (Airlink
or Lantronix UDS-10) then the
phone number should start with a T,
enter the port number after a /.
Eg T
Note that the Airlink and
UDS-10 need to be
configured to operate in
the modem emulation
ii) Not all modems will
autodetect the baud rate
correctly. When using
these modems, make
sure that the baud rates
Note: The SNB900 only supports
rebroadcast of CMR+ messages
The base station can be any system
that supports modem connections
Modem directly connected to the
Base GPS Receiver
Modem connected to the modem port on a SNB900. The SNB900 is connected to the base GPS
The GPS receiver is connected to the Trimble GPSBase software. GPSbase allows for support of
more than a single rover.
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6) To use a Trimble VRS, Check
the Send Position box in the
VRS Position section.
1. Check the Send Position.
2. Enter the WGS-84 Latitude,
Longitude and Height for the
desired position of the VRS.
The position does not have
to be the position of the
radio, you should choose a
position that is in the center
of the operational area
3. The height entered does
need to be within 10m of the
correct value.
7) Getting the Lat, Long, Height
1. Using a MS-750, the front
panel displays the Lat, Long,
2. With SCS900, the easiest
way to get a Lat, Long,
Height. Is to start the
receiver as a base station.
The Lat/Long/Height will be
displayed at the end of the
8) Select the Meters or Feet radio
button to indicate what units the
height is given in.
Note: If you connect to a VRS and do not configure the SNB900 to send the position then the VRS will
drop the connection after approximately 60 seconds. The behavior of incorrectly sending a position
outside the VRS coverage area depends on the VRS server configuration.
Sending positions to a Non VRS system will not cause problems.
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NTRIP is a method for providing user names and passwords for internet based connections, for circuit
switched connection caller ID is used. NTRIP is often used for VRS connections, but can also be used
for Single base line operations
The Trimble SNB900 does not directly support internet based connections, an Airlink Raven or Redwing
modem is used for cellular connections. A Lantronix UDS-10 is used for Wired connections
9) If the Server requires NTRIP,
select the Use NTRIP box.
The SNB900 can be used to
connect to remote bases using
10) Enter the Username, password,
and correction stream for the
NTRIP server.
11) Click Set. The configuration is
updated. A status dialog shows
when the configuration is
The SNB900 will now automatically attempt to dial out when a modem is connected.
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SNB900 Modem Connection information displayed
The Modem status information on the SNB900 is accessed by pressing the up or down arrows.
From the main status screen, press the down arrow twice to see the status information. Modem status
information follows the CMR reception stats
Note that if pressing the down arrow twice displays the firmware version number, then the Trimble
SNB900 is not configured in Easy IP mode. Change the mode of operation by using the Next button.
The SNB900 will display the following information when connecting to a RBS or VRS.
Note: The phone number to be dialed alternates with the modem status
1) Idle:
The modem is not currently in use. This is normal between connection attempts. If the
SNB900 does not change to one of the other states within 60 seconds this indicates a cabling
problem. The SNB900 will not attempt to dial unless a modem is connected to the unit. (A full 9 pin
modem connection is required)
2) Initializing: The SNB900 is sending the initialization commands to the modem, if Initialization is
successful the SNB900 will dial next. If the SNB900 does not move to dialing check the
configuration and baud rates of the modem.
3) Dialing:
4) Dialed:
The SNB900 is sending the phone number to the modem
Modem has dialed and the SNB900 is waiting for the remote to answer.
5) Connected: The remote has answered.
6) Disconnect: The modem has disconnected for some reason, the SNB900 will automatically attempt to
Connection Methods
There are 5 major options for connections
1) Cellular Circuit Switched Connections
2) Internet Based Cellular Connections
3) Land Line Circuit Switched connection
4) Lease Line connections
5) Internet Based wired connections
These methods all have different advantages and disadvantages.
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Cellular Circuit Switched Connections
Generally the easiest system to get working with the least amount of field infrastructure.
Often highest cost, although some cellular providers allow unlimited cell to cell calling
Medium level of Latency and variability in latency.
Internet Based Cellular Connections
Not directly supported by the Trimble SNB900 at the moment, requires an Airlink Raven or
Redwing modem.
Generally low cost
High variance in latency.
Land Line Circuit Switched connection
Generally the easiest system to get working when there is an analogue phone on site.
Costing depends on local calling area and plan.
Low level of Latency and variability in latency.
Lease Line connections
Requires special installation by the telecom company.
Costing depends on local provider and distance between locations. Can often be very cost
Low level of Latency and variability in latency.
Internet Based wired connections
Not directly supported by the Trimble SNB900 at the moment, requires a Lantronix UDS-10
Generally low cost, the connection can also be used for other services.
A medium variance in latency depends on connection.
VRS and 2 Way Data
At this time there is not a cabling solution that support modem connection and 2 way data. Both
of these solutions use the 26 Pin port.
Generally on sites that 2 Way data is being used, a local base station solution would be a better
solution. A VRS rebroadcast solution does have a PPM error from the VRS position in use.
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