Skytraq s1315f-raw (under the magnifying lens)

Hi,

Lately I have been working with one of the few mass market receivers which outputs raw observables: the Skytraq S1315F-RAW. The only other "low cost" alternative to it is the uBlox LEA-4T, LEA-5T, and LEA-6T.

My purpose was to assess its capabilities, to understand if there are applications in which this device can really be useful. I don't know the answer yet, but I can publish some preliminary results obtained with RTKLIB.

So, I assembled a few of these on a board together with a FT232RQ UART-to-USB transceiver and run Cutecom on my Linux machine.

Figure 1: Yuan10 20-Hz raw measurements GPS receiver.

To my surprise, this does not work like the uBlox chips, which can output both NMEA and binary. The S1315F-RAW only outputs binary data. The news you don't read anywhere else is that the observations are taken at 20Hz, and do not include a PVT solution. Also, the clock bias is let running free and therefore the measures can be quite far off (tens of milliseconds) the real GPS time.

Ultimately I wanted to know what is the quality of the carrier phase, since this will tell if the receiver is fit for low-cost RTK applications.


Scenario 1: Zero Baseline, Open Sky

Figure 2: Zero baseline track results in 1 hour.

Figure 3: Zero baseline ENU results in 1 hour.

Scenario 2: Short (known) Baseline, Open Sky
To be done still :)

Comparison 1: Orcam GPS-26 OEM (SiRF Star II)
Using the board below I collected RAW observables (pseudorange, carrier phase, Doppler, and C/N0) from two SiRF Star II receivers.

Figure 4: Dual SiRF Star II receiver board assembly

I wrote a simple SiRF binary to Rinex3 parser and the observations look like:


but unfortunately RTKLIB refuses to process the raw measurements and I am still trying to work out why!

Anyway, the first results with the S1315F-RAW seem promising enough, showing 2-3 cm errors in Kinematic mode. More will come on this post soon.

Cheers,
Michele