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Technology Stocks : Trimble Navigation -- Ignore unavailable to you. Want to Upgrade?

To: David who wrote (1967)	12/9/1997 1:26:00 AM
From: Petz	Read Replies (1) \| Respond to of 3506

David, <quart-assisted GPS or GPS-assisted quartz?> I'm not sure what the distinction is. Wasn't the accuracy spec 50 nsec? The very best quartz clocks could only hold this accuracy for a couple of minutes, but a good GPS receiver should be able to correct the clock accurately several times per minute. The biggest problem I see for a GPS-corrected crystal clock is the military SA (accuracy degradement to civilian receivers). It may add 100 nsec RMS or more of error to the GPS time. There are several ways the Trimble clock may be getting around this: 1. Use surveyed location for clock or very long term averaging (days) of clock location (setup difficulties) 2. Use long term averaging (longer acquisition time) 3. Use publicly available WAAS (full land coverage not in place yet) 4. Use paid differential correction service. 5. For cell phone applications, absolute time accuracy may not matter if nearby base stations have the same time bias. My guess is that Trimble almost certainly uses (2), and possibly some combination of the others. I have no doubt that TRMB is ahead of HP in tackling this kind of problem. BTW, even a Rubidium clock on its own couldn't maintain 50 nsec accuracy with respect to UTC time for longer than about a week (for a GPS satellite-quality clock). Petz