I need a relatively stable timebase against which to calibrate my own *local* timebase.
Assume *my* environment is reasonably well controlled (temp, etc.).
Also, assume I can make measurements over VERY long periods of time (24/7/365 duty).
Ideally, I would like the choice of reference to be something that user could trade cost/convenience/performance.
To that end, I've got a few basic ideas:
- local XTAL (too easy to "pull", no real advantage over TCXO)
- local TCXO (overkill -- hard to make this "optional")
- external PPS input from GPS (requires view of sky, expensive)
- network time service (hole in firewall, latency issues)
- LFC (low accuracy but dirt cheap, LONG integration periods)
To be clear, I am calibrating *time* -- beyond that is my own concern.
Any other ideas I should entertain?