This is correct, to the sense that a working GPSDO has sufficient status information that you know with great probability of being right when the device operates per specification, particularly when there is a good GPS signal available from several satellites (3 minimum, 5 is good, more is better).
The actual performance may be affected by a number of factors which may not immediately generate an alarm, yet may cause the device to operate at the limits or maybe even outside the specification for a short time, and for some people or some applications, that could be a problem. That's when having more than one unit is helpful. My original comment about needing 3 or more units was a little bit tongue-in-cheek, but considering this is the Time-Nuts mailing list, maybe not completely out of place :-) That's what a lot of discussions on this mailing list have centered around recently, and I find this area very interesting and challenging. So, if you simply want a good reference for your instrumentation, a stock Thunderbolt and a well placed antenna will be great, and per specification will get you within 20nS of UTC (at 1 sigma) and within 1e-10 in a second or more (almost 1e-12 in a day) as long as there are GPS signals. More impressively (compared to other units in a similar price range), it will drift less than 1uS/hour in holdover mode (no GPS signal) once stabilized for a day or so (per specification). I think the Thunderbolt was designed for cellular base station applications and therefore is a pretty dependable and reliable unit. Mine has been running 24/7 since November and based on it's data output, has been consistently within a few nS of what it thinks UTC is. That's good enough for me. Didier KO4BB PS: when you install and power up a Thunderbolt for the first time, it will do a self-survey to determine it's position. Depending on the quality of the GPS signal, it may take from one to a few hours. Once that's done, you will know it's location with great precision. You can then save it to EEPROM using the Trimble software, which will make re-acquisition (if you loose power) faster the next time. John Miles wrote: > To answer the original question, a Thunderbolt or similar GPS standard is > MORE than capable of telling you if it is working properly. There is no > reason to use more than one of them at a single location. The Trimble > software will tell you how many nanoseconds the 1-PPS output is off, and how > many parts per billion the 10-MHz output is off, compared to what GPS says > they should be. And there are numerous diagnostic alarms that are monitored > continuously. > > It is a plug-and-forget device, except that you do want to set the saved > location and environment (trees, fixed/mobile, etc.) properties when you > install it. > > -- john, KE5FX > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts