GPS - Frequently Asked Questions
Q: What are the differences between the SGR-05U and SGR-05P?
A: The SGR-05U is a University-Grade GPS receiver, and is a modified terrestrial GPS receiver that is intended to be low cost and rapid delivery. The SGR-05U is in stock for rapid delivery, but UK export licensing can take up to 3 months.
SGR-05P is the Professional-Grade version. It uses the same core technology, but is designed for space. It has TMR protected memory to make it more robust under SEUs, an A/D converter, and non-volatile RAM to improve the Time to First Fix.
Q: Do the receivers have SAASM capability?
A: The SSTL GPS receivers have no SAASM capability, and are L1 C/A code only.
Q: In the event Selective Availability (SA) is turned on by the Department of Defense, how would the dithered GPS signal affect the PVT solution calculated by the receiver?
A: The receiver will continue to operate and produce PVT under SA (assuming the characteristics of SA are the same as previously). From past experience, if SA were to be re-enabled, the position accuracy would degrade from 10 metres typical to approx 50 metres (95% 3D). The SST algorithms have changed since SA was turned off, so we are less sure about the effects of velocity and time degradation, but would expect velocity to degrade from 0.5 m/s typical to 2 m/s, and time from 0.5µs typical to 1 µs.
Q. Is time tagged carrier phase data available to the user?
A. Yes, all SSTL GPS receivers can output time-tagged phase data on request.
Q: Is it possible to use a different interface (e.g. RS485 or SPI) with the SGR-05U and SGR-05P?
A: The SGR-05U and the SGR-05P both have a UART interface, utilizing TTL levels. It would be possible to connect this to an RS485 or RS422 channel via appropriate interface chips, but neither receiver is designed to be operated over SPI.
Q: Is an antenna supplied included with the receivers, or does it need to be purchased separately?
A: An active patch antenna is provided with each SST GPS receiver, except the SGR-05U.
Q: What testing is carried out on these modules pre-integration?
A: The baseline price includes functional performance testing according to SST test procedures and includes the following additional testing:
- Workmanship level vibration testing to verify workmanship – with pre- and post functional performance testing.
- Thermal cycling (in ambient pressure) over the operational temperature range - undertaking 3 thermal cycles with functional performance testing at temperature extremes on the final cycle.
Testing beyond the scope of that mentioned above is available and is negotiable on a case by case basis.
SGR-05U testing bypasses some standard SST QA processes (QA reporting minimized), but the unit is still inspected and tested using SST processes.
Q: Have reliability calculations been carried out on the SST receivers?
A: Reliability has been calculated for the SGR-07 (which contains the SGR-05P) and the SGR-10. Assuming single string and 5 years lifetime, reliability for the SGR-07 is 0.928, and SGR-10 is 0.907. It has not been calculated for the SGR-05P, but should be better due to this module having fewer components and no DC/DC converter.
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