Affordable RTK Capable GPS Receiver

We are pleased to announce availability of NS-HP, a $50 RTK-capable high performance GPS receiver. At 2 / 4 / 5 / 8 / 10 / 20 / 25 / 40 / 50 Hz update rate, NS-HP is a high-performance GPS receiver suitable for traditional GPS applications. At 1Hz update rate, NS-HP can accept RTCM 3.x message type 1002, 1004, 1005, and 1006, or SkyTraq raw measurement data from a base station to perform carrier phase RTK processing, achieving centimeter-level accuracy relative positioning.

When set to base mode, NS-HP output GPS carrier phase raw measurement data, the base antenna location can be set using binary command or can be self-surveyed.

Below figure show road test RTK performance of NS-HP driving on a road with clear view of the sky, back and forth on the inner lane 3 times, each time using one of three different antennas placed at the same location on the roof of a car. The antennas used are Harxon HX-CSX601A survey grade antenna, Tallysman TW2710, and a low-cost tri-band antenna. The baseline varies from 1.6Km to 2.5Km. Each color represents testing done using a different antenna. Although we tried to keep the vehicle on center of the lane, it’s not easy driving manually; the figure shows variation less than 40cm driving on the same road 9 times.



Below shows result using a popular brand normal GPS/GLONASS receiver; as expected the variation is much greater than an RTK receiver.


Static test scatter plot of 5 minutes RTK fix solution w.r.t. baseline is shown below; with centimeter-level precision.


Minimum hardware connections needed for NS-HP are:

UART1 TX1:    to output NMEA result

UART2 RX2:    to input base station data (not needed for non-RTK use)

VCC33:            3.3V power

GND:                ground

RFIN:                connect to GPS antenna


Using a Bluetooth serial module (2.1 EDR) connecting to TX1 and RX2, running NTRIP client software (Lefebure) on Internet-connected Android smartphone, setting smartphone Developer Options to allow mock locations enabling use of external GPS, one can immediately upgrade their Android smartphone GPS with high-precision RTK capability, one step toward "The Democratization of Accuracy (”, an interesting blog by Brent Jones. Mobile GIS data collection on Android smartphone using cloud-based software ( would be possible.


Connecting RX2 to wireless radio to receive base station data, the NS-HP TX1 NMEA output can be used for outdoor precision machine control in the fields.


For base station data, it can come from public/private RTK base station within 10Km retrieved using a NTRIP client, public/private RTK base station that provide virtual base station (VBS) service then distance can be relaxed, or using another locally placed NS-HP in base mode.


The only catch with NS-HP is that, it’s GPS-only, time to RTK fix (TTRF) can vary w.r.t. GPS satellite availability and orientation as below figures show. We in Asia see many GPS + BDS satellites combined, TTRF is consistently much shorter with GPS/BDS RTK receiver. For GPS/BDS RTK receiver users in the US, due to currently very few BDS satellites visible, GPS/BDS RTK will behave like GPS-only RTK; users will see performance improvement over the years as more BDS satellites are put into orbit from 2016 ~ 2020, until BDS becomes fully operational in 2020.





NS-HP uses carrier phase measurement to achieve centimeter-level accuracy. Compared to normal GPS receiver, NS-HP is much less resistant to noise, noise level that normal GPS still function reasonably well the NS-HP likely will not able to get RTK fix but will have float or single solution, giving similar accuracy as a normal GPS receiver. Thus for UAV application, unless hardware could be redesigned with shielding to minimize noise radiation, ad hoc method might be needed to get NS-HP to work on a UAV (including placing antenna at different location, using RF absorber, changing board-level module to other brands that doesn’t interfere...).


Other known issues with NS-HP for RTK applications are:
1. Single-frequency RTK works within 10Km baseline
2. Operate only under open sky
3. Require 6 or more satellites above 15degree elevation angle with good satellite geometry
4. Require signal over 38dB/Hz


NS-HP is available for pre-order on the NavSpark website. First batch of 50pcs pilot production ships out on December 15.


Thank you for your interest!


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