Base station operation guidelines

This topic introduces the concept of base station 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.

Real-Time Kinematic (RTK) operation provides centimeter-level accuracy by eliminating errors that are present in the GNSS 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.

A base station consists of a receiver that is placed at a known (and fixed) position. The receiver tracks the same satellites that are being tracked by the rover receiver, at the same time that the rover is tracking them. Errors in the GNSS system are monitored at the fixed (and known) base station, and a series of position corrections are computed. The messages are sent through a radio link to the rover receiver, where they are used to correct the real time positions of the rover.

Base station components

The base station has the following components:

  • GNSS receiver

  • GNSS antenna

  • Base station radio

  • Power source

GNSS receiver and GNSS antenna

The base station GNSS receiver can be one of following types:

  • A GNSS smart antenna, such as the SPS985/SPS986, that incorporates a GNSS receiver, GNSS antenna, power supply, and radio into a single compact unit. A GNSS Smart antenna can be rapidly set up on a tripod, fixed height tripod, or anywhere that is convenient on the jobsite.

  • A modular receiver, such as the SPS855, that incorporates a GNSS receiver, power supply, and radio in a single unit. The GNSS antenna (and, optionally, the base station radio antenna) is separate from the receiver. Because the GNSS antenna is separate, you can use the following optimized components:

    • a geodetic antenna with large ground plane, to eliminate multipath (the major source of GNSS errors) at the base station

    • a high-gain or directional radio antenna, to increase broadcast range and to provide maximum coverage

      You can also place an SPS modular receiver in an easily accessible and secure location, safe from theft and the weather, while the antennas are placed high on a tower or building, clear of obstructions and able to deliver maximum performance.

You can use either type of receiver in a permanent, semi-permanent, or daily quick setup configuration. If semi-permanent or permanent operation is required, however, the modular receiver delivers significant advantages.

Base station setup guidelines

For good performance, observe the following base station setup guidelines:

  • Place the GNSS receiver in a location on the jobsite where equal range in all directions provides full coverage of the site. This is more important on larger jobsites, where the broadcast range of the base station radio may limit the operations of the system.

  • Place the GNSS antenna in a location that has a clear line of sight to the sky in all directions. Do not place the antenna near vertical obstructions such as buildings, deep cuttings, site vehicles, towers, or tree canopy.

  • Place the GNSS and radio antennas as high as practical. This minimizes multipath from the surrounding area, and enables the radio to broadcast to the maximum distance.

    The GNSS antenna must have a clear line of sight to the sky at all times during operation.

  • Choose the most appropriate radio antenna for the size and footprint of the site. The higher the gain on the antenna, the longer the range. If there is more focus on the transmission signal, there is a reduced coverage area. A 3 db or 5 db gain antenna provides a mix of good range and reasonable directional coverage.

  • Make sure that the GNSS receiver does not lose power. The GNSS receiver has an integrated battery that must be charged. To operate continuously for more than a day without loss of power at the base station, provide external power. Sources of external power include:

    • AC power

    • 12 V vehicle battery

    • Trimble custom external battery pack

    • Generator power

    • Solar panel

      When you use an external power supply, the integrated battery provides a backup power supply, enabling you to maintain continuous operation through a mains power failure.

      When the GNSS receiver is connected to a power source that can support the power drain, the integrated battery is continuously charged from the connected power source. This helps to ensure that the battery stays charged (SPS Modular only).

  • Do not locate a GNSS receiver, GNSS antenna, or radio antenna within 400 meters (about 1,300 feet) of:

    • a powerful radar, television, or cellular communications tower

    • another transmitter

      Cell phone towers can interfere with the base station radio broadcast and can stop corrections from reaching the rover receiver. High-power signals from a nearby radio or radar transmitter can overwhelm the receiver circuits. This does not harm the receiver, but can prevent the receiver electronics from functioning correctly.

      Low-power transmitters, such as those in cell phones and two-way radios, do not interfere with receiver operations

  • Do not set up the base station directly beneath or close to overhead power lines or electrical generation facilities. The electromagnetic fields associated with these utilities can interfere with GNSS 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

  • Place the GNSS receivers in a protected and secure location. If the base station is in the center of a jobsite where heavy machinery is operating, place flags around the base station to warn operators of its existence.

  • If you place the receiver in a lock box on the jobsite to protect the receiver from theft or from the weather, shield the lock box from direct sunlight and provide ventilation for the receiver through an inlet and extractor fan. A receiver that has a broadcast radio generates significant heat. Do not allow the temperature in the box to exceed 50 °C (122 °F).

    If working in a cold climate, you may need to provide heat to the receiver. Do not operate the receiver below –40 °C (–40 °F)

  • Trimble recommends that, wherever possible, you keep GNSS receiver equipment dry. The receivers are designed to withstand wet weather, but keeping them dry prolongs their life 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. Avoid exposing the receiver to corrosive liquids and salt water wherever possible.

  • Trimble recommends that you install lightning protection equipment at permanent base station locations. Equipment should include a gas capsule lightning protector in the GNSS and radio antenna feed line and appropriate safety grounding. A static dissipater near the antennas can reduce the likelihood of a direct lightning strike. Also protect any communications and power lines at building entry points. For more information, contact your local Trimble dealer, or go to the Huber and Suhner website (www.hubersuhnerinc.com).

  • Trimble recommends that you use surge protection equipment on all permanently installed equipment.