Way back on June 30th, Stephan asked: A number of recent entries to this list have mentioned topics relating to GPS timing and environmental corrupting factors (e.g. Ionosphere, Temp., Humidity, etc.). Personally, I am very interested in setting up a very precise relative time between locations (maybe 100s of meters to 10s of kilometres apart) on time scales of (maybe 100s of seconds to 10s of minutes). I noted some members referred to dual frequency receivers for overcoming these effects. Can anyone point me to some literature, articles or links to overcome these environmental factors?
Sorry to be slow in responding. I'm just getting to the July pile of Email! You might find some tests that Rick Hambly (see [1]http://cnssys.com) and I did on a 22 km baseline across Washington, DC. See the paper "Critical Evaluation of the Motorola M12+ GPS Timing Receiver vs. the Master Clock at the United States Naval Observatory, Washington DC." at [2]http://www.gpstime.com/. You will see (in Fig.7) that we obtained ~2 nsec RMS syntonization for 6+ days despite a ~50 nsec ionospheric disturbance that happened during a major storm & aurora event. In the paper you will also see that, at least for the 4 receivers tested at USNO, the different receivers showed ~5 nsec "absolute" agreement without calibration. Of course, I would recommend that you run a zero-baseline calibration verification on the different receivers if the "absolute" offset is important. You also asked about the use of simple, single frequency receivers instead of professional, dual-frequency surveying instruments. The basic answer is cost and simplicity. The board-level single frequency receivers cost a few hundred dollars, while the professional instruments are in the $5-10,000 range. The single frequency instruments produce 1PPS pulse outputs that can be used "now" while the professional instruments require post-processing of the data {the 1PPS "now" outputs from the professional instruments are AFAIK derived from the single frequency L1 data}. You might find the other papers [especially "Low-cost, High Accuracy GPS Timing" and "Timing for VLBI (2005)"] to be of interest to see how we have used the board-level (especially Motorola) receivers. Recently Motorola has dropped the production of their ONCORE receivers; Rick and I are in the process of examining the successor iLotus M12M Timing receiver (see [3]http://www.synergy-gps.com/images/stories/pdf/m12m%20timing%20preli m%20v11.pdf) and plan to report on the tests at this December's PTTI meeting. 73, Tom References 1. http://cnssys.com/ 2. http://www.gpstime.com/ 3. http://www.synergy-gps.com/images/stories/pdf/m12m%20timing%20prelim%20v11.pdf _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts