Hi Tom, Kevin, the JLT DROR GPSDO mentioned by Kevin in the original email may be overkill for this application, as it is designed to provide very low phase noise under extreme vibration conditions, and it is state-of-the-art technology and priced accordingly. It is designed to interface directly with a vehicle power supply, so that may help in simplifying the installation. Phase Noise doesn't seem to be a requirement here, and we do have a "standard" version that does not have the phase-noise-under-vibration cleanup loop installed to save substantial cost. It should work quite well in the application, as it has various extremely low-g-sensitivity oscillators on board that will keep drift to very small values even under very large acceleration and vibration, and temperature changes. It was designed to be essentially indestructible. If cost is an issue, we have ultra-low-g versions of our FireFly-IIA products available (our g-force product line) that are designed and tested to provide a guaranteed holdover under the conditions that Tom mentions below. They are designed to guarantee drift in "backpack" type applications without GPS, but with lot's of thermal changes and a very wide temp range, loads of acceleration (shock, vibration, and tilt), and fast warmup. To give an example, we can achieve better than 0.1ppb per g per axis acceleration sensitivity on the worst-case axis on our g-force products. So for example the FireFly-IIA g-force would have the following drift in a hypothetical high-g application: g-force on average over entire trip - 3g (this extreme acceleration would never happen in reality of course) average thermal change - 40 Degrees C allowed warmup time with GPS - 1 hour Drift over 5 hour mission: 3g x 0.1ppb/g + 40C * 0.005ppb/C + 0.1ppb initial error = 0.6ppb overall average error over 5 hours So in this extreme scenario we have 0.6ppb * 5 * 3600 = 10.8 microsecond drift over 5 hours. Aging and retrace is not taken into consideration here, but that should be more than compensated by the unrealistic constant 3g acceleration error we added to the calculation. The cost of our g-force products is only about 2x to 2.5x the price of our standard DOCXO products. bye, Said In a message dated 3/9/2011 12:11:49 Pacific Standard Time, t...@leapsecond.com writes:
Some GPSDO "learn" their hold-over parameters over time, sometime days, in which case you may be in for a surprise. Is there any way you can simulate the temperature, vibration, and g-force (or lack of) trauma that the GPSDO is going to experience during this hour of launch-to-orbit? If not, I suggest a simple test: just throw your GPSDO and battery in a backpack and go jogging. Twirl the backpack in the air every now and then. After an hour I'd be very curious by how many microseconds it's off. /tvb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.