Rover operation guidelines (SPSx61)

GPS Real-Time Kinematic (RTK) operation provides centimeter-level accuracy by eliminating errors that are present in the GPS system. For all RTK, Location RTK, or DGPS operations, you require both a rover receiver and a source of corrections from a base station or network of base stations.

This topic introduces the concept of rover operation, provides information to help you identify good setup locations, describes best practices for setting up the equipment, and outlines the precautions that you need to take to protect the equipment.

The second part of an RTK GPS system is the rover receiver. The rover is capable of receiving correction streams from different sources and by different methods to improve the precision of the position calculation. The rover receiver is mounted on a pole, vehicle, marine vessel, or construction machinery, and provides position information for the operator. The rover receiver may be connected to a base station or to some other source of corrections such as a VRS system, SBAS, Beacon, or an OmniSTAR service. The connection can be provided by:

  • an integrated radio (UHF or MSK Beacon)
  • an external cellular phone that is connected to the receiver either by Bluetooth wireless technology or by means of a cable
  • through satellite reception (SBAS or OmniSTAR)

Rover receiver components

The rover receiver has the following components:

  • GPS receiver
  • Two GPS antennas (L1/L2/Beacon/SBAS/OmniSTAR)
  • Optional integrated UHF radio receiver for RTK operations
  • Optional MSK Beacon receiver for DGPS operation

Rover receiver setup guidelines

For good rover operation, observe the following setup guidelines:

  • Place the GPS antennas in locations that have a clear line of sight to the sky in all directions. Do not place the antenna near vertical obstructions.
  • Place the two GPS antennas at least 2 meters (6.5 feet) apart and at approximately the same height.

  • Place the GPS and radio antennas as high as possible to minimize multipath from the surrounding area. The receiver must have a clear line of sight to the sky at all times during operation.

    The GNSS receiver and its cabling should be installed in accordance with all national and local electrical codes, regulations, and practices. The receiver and cabling should be installed where they will not become energized as a result of falling nearby power lines, nor be mounted where they are subjected to over-voltage transients, particularly lightning. Such installations require additional protective means that are detailed in national and local electrical codes.

  • The SPS461 can optionally track the GPS L2C modernization signal. The signal helps you to get positions at the worst times of the day and in the worst GPS locations, but does not guarantee that you will.
  • Loss of the satellite signals or loss of the radio link will result in a loss of position accuracy. The Position mode will reflect this change and depending on the correction inputs available will show one of the following modes:
    • RTK Fixed – The rover has been upgraded to Precision RTK and has initialized using a valid RTK correction stream.
    • Location RTK – The rover has been upgraded to Location RTK and has initialized using a valid RTK correction stream.
    • OmniSTAR HP/XP – The rover has been upgraded to Location RTK, has a valid OmniSTAR subscription, has locked onto an OmniSTAR satellite beam, and is decoding the XP or HP correction service.
    • OmniSTAR VBS – The rover has a valid OmniSTAR subscription, has locked onto an OmniSTAR satellite beam, and is decoding the VBS correction service.
    • Beacon DGPS –The rover is locked onto a Beacon reference station and is receiving valid DGPS RTCM correction messages (Type 1 or Type 9).
    • DGPS – The rover is decoding DGPS RTCM corrections from an external source.
    • SBAS – The rover is decoding corrections from an SBAS source.
    • Autonomous – The rover has no source of corrections and is working by itself with the available GPS signals.
  • On a vehicle or marine vessel, place the GPS antenna in a location as free from shock and vibration as possible. Use either a magnetic mount or a 5/8" thread bolt in a suitable location.
  • Do not locate the receiver or antenna within 400 meters (about 1,300 ft) of powerful radar, television, cellular communications tower, or other transmitters or GPS antennas. Low-power transmitters, such as those in cellular phones and two-way radios, normally do not interfere with receiver operations. Cellular communication towers can interfere with the radio and can interfere with GPS signals entering the receiver. This does not harm the receiver, but it can prevent the receiver electronics from functioning correctly.
  • Do not use the rover receiver directly beneath or close to overhead power lines or electrical generation facilities. The electromagnetic fields associated with these utilities can interfere with GPS receiver operation. Other sources of electromagnetic interference include:
    • gasoline engines (spark plugs)
    • televisions and computer monitors
    • alternators and generators
    • electric motors
    • equipment with DC-to-AC converters
    • fluorescent lights
    • switching power supplies
  • Trimble recommends that, wherever possible, all GPS receiver equipment is protected from rain or water. Although, the receivers are designed to withstand all wet weather conditions, keeping the receivers dry prolongs the life of the equipment and reduces the effects of corrosion on ports and connectors. If the equipment gets wet, use a clean dry cloth to dry the equipment and then leave the equipment open to the air to dry. Do not lock wet equipment in a transport case for prolonged periods. Wherever possible, avoid exposing the GPS receiver to corrosive liquids and salt water.
  • If you are using the rover receiver in open spaces, Trimble recommends that you stop work during electrical storms where the risk of lightning strike is high.
  • Where cables are involved, Trimble recommends that you use cable ties to secure the cables to the rod or other equipment to avoid inadvertent snagging while moving about the jobsite. Be careful not to kink, twist, or unnecessarily extend cables, and avoid trapping them in vehicle doors or windows. Damage to cables can reduce the performance of GPS equipment.

Internal radio setup for rover operations

The internal receive only radio of the receiver is delivered with no radio frequencies preprogrammed into the receiver. To add receive (Rx) radio frequencies to 450 MHz radios, use the WinFlash utility or web interface (see Adding UHF Internal Radio Frequencies). Network channels can be selected for the 900 MHz radios.

Once the radio frequencies are configured, use the controller or receiver to select channel frequencies during rover setup operations.