Common ways to set up a base station

You can set up a base station in different ways depending on the application, coverage area, degree of permanence versus mobility, and available infrastructure. Before you set up a base station, please see the Setup Guidelines.

Setting up a base station for permanent or semi-permanent installation

For construction applications, where machine and site positioning operations using GPS will be carried out over a long time (weeks, months, or years), ensure that you choose the base station location carefully.

A semi-permanent or permanent base station helps to eliminate the types of error that can result from repeated daily setups, and ensures that you always use the GPS antenna at the exact original location. The requirement for a permanent base station setup increases as more receivers that use the base station as a source of corrections, increases the cost of any base station downtime.

On the largest jobsites, and on those that remain operational for the longest time, a permanent or semi-permanent installation is a popular solution. A SPS Modular receiver is typically used as the base station, located in a site office or trailer where it is easy to access (to check or configure), and where it is secure from theft and the weather. The GPS and radio antennas are normally mounted on a permanent structure on the roof of the building, where they are high and clear from obstructions and where the radio antenna can provide the maximum range of operation.

Trimble recommends that you use the Trimble Zephyr Geodetic Model 2 GPS antenna. This antenna has a large ground plane that reduces multipath, providing the best GPS performance at the base location. The antennas are connected to the receiver by high quality RF cables.

The receiver is connected to a permanent power supply (mains or generator power). The internal battery of the receiver is always being charged, and acts as an uninterruptible power supply if there is a power failure. In some cases, the receiver may also be connected by an Ethernet cable to the Internet (either through the SNM920 radio or a router), so that it can be monitored and configured from a remote location, and can warn an administrator by email or text message if there is a change to the configuration or status. In these situations, the receiver can transmit corrections to a remote radio or receiver over the Internet, for rebroadcast requirements, without using repeaters.

 

SPSx51 receiver pemanent installation

SPS Modular receiver permanent installation

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 SPS882 Smart GPS antenna is also often used. Simply mount the Smart GPS antenna on the T-Bar, and optionally connect to an external power supply 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.

System set up on a T-bar showing an external radio antenna to gain longer range

Setting up a mobile base station: Tripod and fixed height tripod

If you are repeatedly moving between jobsites, or if you are visiting a jobsite for the first time before a T-Bar or similar setup can be established, Trimble recommends that you use either a tripod and tribrach setup, or a fixed height tripod.

The fixed height tripod is quicker and easier to set up over a control point. It allows you to re-establish the antenna height exactly so that the receiver can be set up faster without using the SCS900 software or without needing to enter a revised antenna height in the receiver front panel. Take great care to ensure that the GPS antenna is set up accurately over the control point, and that the GPS antenna height is measured accurately, in the right way (vertical or slope height) to the right location on the antenna (base of antenna or to a specified location on the antenna). When you start the rover receiver, it is extremely important to check in, at one or more known locations, to check for possible position or height errors. Checking in at a known location is good practice and can avoid costly errors caused by a bad setup.

Typically, the tripod and fixed height tripod methods do not give significant height clearance above the ground, and can reduce the range of operation caused by radio limitations.

Tripod and tribrach setup

In the tripod setup, the tripod is located over the control point, and the tribrach and tribrach adaptor is mounted on the tripod and centered over the point.

  1. Mount the GPS antenna on the tribrach adaptor.

SPS882 only: If you are using a Smart GPS antenna, use the 25 cm spacer rod provided with the Base Station Accessory kit. This allows the radio antenna in the receiver to clear the head of the tripod.

  1. SPS Modular only: Clip the GPS receiver to the tripod.
  2. SPS Modular only: Connect the GPS antenna to the receiver using the appropriate cable.
  3. If required, connect the GPS receiver to an external 12 V power supply. Use the crocodile clip cable or the Trimble custom power pack.

SPS Modular with a low-grain "rubber duck" antenna

SPS Modular with an external high-gain antenna

SPS882 with an internal 450 MHz Tx radio

Tripod and tribrach setup

Fixed height tripod setup

A fixed height tripod setup is similar to a tripod setup, but is simplified by the central leg of the tripod, that is placed directly on the control point. If the central leg is leveled accurately, the fixed height tripod is quick and easy to set up, and provides an accurate way to measure the true antenna height.

  1. Set up the tripod over the control point.
  2. Attach the GPS antenna to the head of the tripod.
  3. If using an external high-gain radio antenna, mount the radio antenna to the radio antenna bracket that is attached to the head of the tripod (beneath the GPS antenna). See the figure below.
  4. SPS Modular only: Hook the receiver to the center leg of the tripod, using the tripod clip.
  5. SPS882 only: Mount the antenna using the 25 cm spacer rod (supplied with the SPS882 Base Station Accessory kit  P/N 50590-50), so that the radio antenna clears the head of the tripod.

SPS Modular with a low-grain "rubber duck" antenna

SPS Modular with an external high-gain antenna

SPS882 with an internal 450 MHz Tx radio on a fixed height tripod

Fixed height tripod setup