Reference station site selection and installation is the most important factor in the success of a permanent reference station. Failure to select a suitable location and failure to properly install the antenna will create downstream issues for the rovers relying on data generated from the stations. This is not a difficult process, but it does have a few rules that must not be ignored.
Site Selection Criteria
- Reference Antenna Location
- Visibility to the satellites. Open sky, 360°, 10° above the horizon
- No obstructions
- No nearby sources of multipath (flat and/or reflective surfaces)
- Radio interference (RFI)
- Secure facility (against theft, vandalism)
- Reliable electrical/power
- Access – maintenance etc.
Internet – level of service, reliability, etc.
Choosing a Site Location
Unobstructed view of the sky: 360°
No distant obstructions: 10° above horizon
No nearby reflective surfaces (multipath)
No nearby RF sources at or near GNSS frequencies:
- Cell towers
- Dispatch radios (police, fire, emergency, taxi, delivery) VHF/UHF
- Automated weather stations
- Microwave transmitters
- Radar (airports, or near airports)
- Television broadcast towers
- High voltage power lines
- Prior to permanently installing a reference antenna, test the location by collecting data and analyzing for the presence of multipath and/or radio interference.
- Using the receiver, antenna, and cable length to be installed, place the antenna as close as possible to the intended installation location.
- Log raw data for 6 hours at a 1 second rate.
- Analyze the raw data for multipath and RFI.
Required Installation Hardware
An antenna installation is rarely the same, and there are always subtle differences in material and location. There is a minimum set of equipment that will be needed to properly install a reference station.
- Hammer drill, rotary drill/screw gun
- Hammer, wire cutter, cable crimp/stripper tool
- Receiver, antenna mount, coaxial cable, nuts, bolts
- Serial, USB adapters, Ethernet
GNSS Antenna Installation
When considering the proper antenna mount, the key points to remember are that the antenna must be stable and plumb. Mount stability is the primary concern. Once the antenna has been positioned, any movement in the antenna will create a ripple effect on rover RTK reliability.
The standard for reference station installations is the CORS Guidelines published by the National Geodetic Survey. These guidelines are established to assist with installing the best possible reference station antenna. However, these guidelines will add costs to the installation. They are a very reliable source of information and should be the model to follow, if possible.
GNSS Antenna Installation
There are 2 basic types of antenna mounts:
- Pillar mount
- Wall mount
The most common in a Real Time Network is the wall mount. Masonry buildings are preferred. Solid brick or reinforced concrete ones are recommended. The building should have been built at least 5 years previously to increase the likelihood that all primary settling of the building has occurred. There should be no visible cracks on the outside or inside walls. Buildings taller than two stories are not recommended. No wood or simple metal frame with metal walled buildings, and metal roofs should be a last resort.
- Steel mounts are recommended for longevity (angle iron or circular pipe). Aluminum is acceptable but has approximately twice the thermal expansion of steel/concrete.
- The mount must be bolted directly to the main part of the building. A load-bearing wall near a corner is recommended.
- The use of epoxy and threaded lock adhesive fasteners (bolts/anchors/rods) is strongly recommended.
- Mounting on a chimney is not recommended unless it has been filled with concrete or if it is particularly robust.
- The mount should not interfere with the building’s replaceable roof. This will minimize the chance that the mount will be disturbed when the roof is replaced.
Attaching laterally to a load-bearing wall:
- The mount should extend about 0.5 m above the roofline and be attached to the building for a length of at least 1 m, with at least 3 anchors/bolts. The ratio of freestanding part to bolted part should be approximately 1:3.
- The bolts/anchors must penetrate directly through the mount, e.g., no u-bolts, channel lock systems, brackets with metal ties/clamps. Spacers to keep the mount from sitting flush against the wall are acceptable.
Attaching vertically to a master wall:
- A bolt or rod must be anchored into a load-bearing wall. Take care not to void a roof warranty.
- Avoid metal flashing on a parapet wall.
Typical exploded diagram
It is also good advice to ground each component of the installation.
The most challenging aspect of any Reference Station installation is the IT segment. It can present challenges from a variety of sources:
- Installers not familiar with IT
- Complex, managed IT environment
The requirements are not complicated and are relatively simple, provided you know what to ask for. Several Quick Guides are available on myTopcon to assist with familiarization.
GNSS Receiver Configuration via TRU
- Connect the receiver to the PC/Laptop. This can be done through the Serial A/B port, with the appropriate cable.
- Launch TRU.
- Once TRU is launched, verify the app is in Receiver Managing mode. This is relatively straight forward by selecting the Device menu and hovering the mouse over the Application Mode option. Receiver Managing should be selected.
- From the Device menu, select Connect.
- Once connected, the settings for the Network configuration are located in the Receiver Settings portion of TRU. Single click Receiver Settings to advance to the next screen.
- There are many options in the Receiver Settings window of TRU. To configure the receiver for a network connection, select the Network icon.
The Network icon opens the dialog box to configure the receiver with the appropriate network configuration. It is important to note that these configuration items must match the local area network in which the MR-2 will reside. If not, the receiver cannot be reached from anywhere in the network. If possible, have an IT professional onsite to assist with assigning an IP address in the LAN subnet.
There are 3 key pieces of information needed.
- This will be the unique address to the receiver.
- Defines the range of IP addresses allowed within the subnet.
- Routes unique IP address responsible for the routing of all devices in the LAN subnet.
After setting up the Network Configuration on the receiver, it is best the verify the TCP settings. From the same Network window, select the TCP tab. There are only 2 fields that need to be verified: Timeout and Password. The Timeout field needs to be set to something greater than zero, and the Password can be set to whatever is desired.
Once these steps are completed, click OK in the upper right corner. TRU will prompt for a reset. Accept and allow the receiver to reset.