The position accuracy of Differential and RTK GPS receivers is improved when using the RT-Base.
Two models of the RT-Base exist; the RT-Base-20 can supply L1 corrections suitable for 20cm positioning and the RT-Base-2 can supply L1/L2 corrections suitable for 2cm positioning. Both models are identical in their operation.
The RT-Base is a self-contained unit that includes:
- The base-station GPS receiver
- Battery suitable for over 10 hours of operation
- Radio modem
- Mains power supply and battery charger
- GPS antenna, 15m cable and tripod
- Radio modem aerial, 5m cable and magnetic mount
The figure above gives an overview of how Differential GPS works. The information from each satellite is measured by both the RT-Base and by the GPS in the car. The RT-Base works out the error in the satellite's information and transmits it to the car using a radio link. The GPS in the car then applies the correction to each satellite's measurement before it computes position and time.
For RTK (Real-Time Kinematic) Carrier-Phase measurements the principle is the same, but the GPS in the car also has to figure out the difference in the number of carrier-phase cycles between the RT-Base and the car. The RT-Base measures the carrier-phase of the signals from each satellite and transmits it to the car.
Differential GPS works in real-time because the corrections from each satellite vary slowly and predictably. The GPS in the car uses a model to predict the error from each satellite. It can update its model when the radio link transmits new data. It is not necessary for the GPS in the car to wait until the radio has transmitted the correction before it outputs its latest value.
For Pseudo-Range (not carrier-phase) Differential GPS the corrections can be up to 60s old (depending on the GPS in the car). For RTK corrections (20cm and 2cm) the corrections can be up to 30s old (again, depending on the GPS in the car).
Different countries have different licensing laws and different frequencies for radio transmissions. Many countries have license-free frequencies that can be used for Differential GPS signals. We can supply a range of different radios that can be used, license-free, in many countries.
DGPS correction type(s)
By default the RT-Base uses the RTCA standard for transmitting its differential corrections.
For more information, please visit our website.