On 12/18/16 3:16 PM, Bob Stewart wrote:
One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on developing my GPSDO without a whole of thought to the user base. It was just a quest for the best result I could obtain with a particular technology. The frequency standard users was a no brainer. Everyone who wants a frequency standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good frequency standard. And then Tom prodded me a bit and showed me the shortcomings of what I was doing, and I did something about it. So, if an NTP user can get his time fix directly from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse?
Anyone who needs to trigger events at a precise time or log the occurrence of an event uses the 1 pps - the serial port (or other interface) gives you the "at the tone the time will be" message, and the edge of the 1pps is the "tone".
I've got several systems flying in space (or soon to fly in space) that use the 1pps from GPS to calibrate their internal clocks and/or to provide an absolute time reference (along with the aforesaid time message).
For example, one needs to have your carrier frequency within a certain tolerance for communications with the ground stations: you can either fly a precision oscillator with an oven (big, heavy, high power) or you can measure a not-so-precision oscillator (small, cheap, low power) against a 1pps, and adjust your frequency that way.
I grant you that this is really more like *building* a GPSDO than *using* a GPSDO.
I've used the 1pps from a GPSDO as a common trigger to synchronize timing and timestamping for separate systems.
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