TinkerNav is available with either the PX1122R or PX1125R SkyTraq receiver. Both use RTCM corrections to calculate an RTK position in the rover mode and compute RTCM correction data in the base station mode. The PX1122R uses data from satellites operating in the L1 and L2 bands, which includes GPS, Galileo, BeiDou, and GLONASS constellations. PX1125R uses L1 and L5 bands, which are supported by GPS, Galileo, and BeiDou satellites. The complete list of supported frequencies for the two receivers and the bands supported by our multi-band GNSS antenna are shown in the table below.
More publicly available, free and paid, correction services support L1 and L2 currently. Also some RTK systems, such as on drones, that you might want to provide corrections for work in L1/L2 bands. Free Precise Point Positioning (PPP), such as Canada’s, which use hours of data to provide a very accurate receiver position, also require L1 and L2 band data. L5 satellites are also newer, so currently more satellites support L2 than L5.
As we will show in this article, there are limited if any performance differences between the PX1125R and PX1122R sensors, so if you plan to run your own base station there is no advantage to the more expensive PX1122R sensor. However, if you plan to take correction data from other sources or use PPP, then make sure you understand what bands those systems support.
To help understand the relative performance of the two receivers in a couple real world situations we setup an experiment.
In the experiments we used two PX1122R and two PX1125R TinkerNav boards. For each receiver type one board was the base station and one was the rover. The ESP32-C3 WiFi radios were used to send correction data from the base stations to the rovers using the software described on our getting started page. Any method of sending correction would work equally well. The antennas for all four boards were placed close together on a ground plane made of aluminum foil.
The experiment monitored the RTK ratio and RTK mode computed by the rover TinkerNav boards over 24 hours of operation for each location. Two antenna locations were used that represented sub-optimal locations in our suburban yard. The first location was 6 ft (2 m) from the corner of a one story section of our house, which was also about 20 ft (6 m) from a two story section of our house and just outside the drip line of two large shade trees to the North and East. The South and West were more open with large trees about 150 ft (45 m) away. For the second location the antennas were moved to within 2 feet (0.6 m) of the edge of the building such that the building blocked the western sky entirely with the two story building 12 ft (4 m) away to the Northwest and the same trees to the North, East, and South.
The TinkerNav rovers logged data every 35 seconds. The two data points logged were the worst RTK Ratio (as computed by the receivers) and the receiver’s lowest mode, with mode 1 equal to GPS, 4 RTK float, and 5 RTK fix, during the 35 second period before the data was logged. This meant that any switch from RTK Fix to RTK float was captured and logged, no matter how brief it was. This gives a worst case picture of how often the receiver entered a degraded mode or had a low RTK ratio. The over 24 hours of data collection for each location ensured that a lot of different satellite geometries were observed.
Location 1: 6 ft (2 m) from Building & Under Tree
In this slightly better of the two locations both receivers performed very well. The PR1125R receiver never left RTK Fix mode while the PX1122R receiver was in RTK Fix mode for over 99% of the time, with only 19 of the over 3000 data points recorded dropping into RTK Float.
RTK Ratio is a metric that the receivers calculate that conveys the quality of the RTK solution beyond RTK mode. Below the RTK ratio for each receiver is plotted below against time (data logging points). The PX1125R had an average RTK Ratio of 8.7 over all data points while the PX1122R had an average RTK ratio of 8.9 for the same time period.
Since the above plot is a bit hard to read with the overlapping data, below is the RTK ratio data plotted as a hysteresis plot showing the number of occurrences for each integer bin of RTK ratio values. This shows the frequency of each value.
In this location the PX1125R maintained RTK mode for the entire experiment, which was over 24 hours, but showed a slightly lower average RTK ratio than the PX1122R. Overall, the performance of the two receivers at this location was very similar.
Location 2: 2 ft (.6 m) from Building & Under Tree
This was the worse of the two locations chosen being closer to the building and having the entire western sky blocked by the building. Still both receivers maintained RTK fixes for over 85% of the time. The image below shows the times that both receivers spent in RTK Float (mode 4) and RTK Fix (mode 5). In total the PX1125R spent 87% of the time in RTK Fix and the PX1122R spent 85% of the time in RTK Fix. The remaining time for both receivers was spent in RTK Float mode.
RTK Ratio is a metric that the receivers calculate that conveys the quality of the RTK solution beyond RTK mode. The RTK ratio for each receiver is plotted below against time (data logging points). The PX1125R had an average RTK Ratio of 7.94 over all data points while the PX1122R had an average RTK ratio of 7.54 for the same time period.
Since the above plot is a bit hard to read with the overlapping data, below is the RTK ratio data plotted as a hysteresis plot showing the number of occurrences for each integer bin of RTK ratio values. This shows the frequency of each value.
For this location the PX1125R and PX1122R again had very similar performance.
Conclusion
The data from this experiment indicates that both receivers have very similar performance in typical suburban environments. If you are planning to operate your own base station the PX1125R is an economical choice that does not impact performance. If you are planning to use third party correction data ensure that it supports L1/L5 bands or purchase the PX1122R that uses the more common L1/L2 bands.