Trimble Outdoors SPSX51 - Manual (Page 47)

SPSx51 Modular GPS Receivers User Guide 45
Setting up the Receiver 5
Setting up a base station for daily site use: T-Bar
For construction applications where a daily setup and takedown of equipment is
required for security reasons, Trimble recommends that you use a T-Bar setup.
The T-Bar consists of a post mounted in concrete (so it cannot move), which has a
solid metal T-Bar mounted to it to provide lateral and vertical separation between the
GPS antenna and radio antenna. The T piece of the T-Bar has a vertical rod at each
end. Each end terminates in a 5/8"
×11 thread to which the antennas can be mounted.
Trimble recommends that one end is clearly marked GPS and the other end is clearly
marked Radio so that at each daily setup, the GPS and radio antennas are mounted at
the same location. Switching antennas by mistake introduces a position error in all
resulting measurements. You can buy the parts you need to make a T-Bar from any
reputable hardware store. Make certain that the T-Bar cannot rotate after
construction. Rotation of the T-Bar can introduce a position error into all subsequent
measurements.
On the upright post, mount either a bracket (to which the GPS receiver can be
mounted), or a well-ventilated lockbox (in which the GPS receiver itself can be
secured).
Each day, mount the GPS antenna on the GPS end of the T-Bar and the radio antenna
on the Radio end of the T-Bar. Connect the antennas to the receiver using the
appropriate cables.The receiver uses its own integrated battery, or an external 12 V
battery through the 12 V crocodile clips cable that are provided with the receiver. If you
choose to use AC power, remember that the heat generated by the charging process
and the radio transmitter increases the need for good ventilation around the receiver.
In such scenarios, an SPSx81 Smart GPS antenna is also often used. Simply mount the
SPSx81 on the T-Bar, and optionally connect to an external battery or radio unit.
Advantages
Use of a T-Bar setup ensures that the base station is set up with exactly the same
position and height every day. This helps eliminate the errors typically associated with
daily tripod setup. For example, wrong antenna height, base not set up over the point,
base set up in the wrong location.