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| GPSDO phase between PPS and clock |
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| Johnny B Good:
--- Quote from: Solder_Junkie on January 05, 2025, 04:23:17 pm ---GLONASS has poorer stability compared to GPS and Galileo. I can’t remember the specification, but given the political situation, it makes even less sense to use GLONASS. Even with an outdoor “mushroom” antenna and a good sky view, I “see” more GPS than Galileo satellites. Ublox recommend sticking with a single constellation for timing use, which also probably applies to frequency too. With my GPSDO measurements I haven’t noticed any difference between GPS, Galileo or both together. SJ --- End quote --- That advice to stick with only one constellation for timing use is just as valid for (stable) frequency reference purposes. The 12 and 24 hour timelapse movies I posted nicely reveal that both types are long term stable frequency-wise. However, a drift in phase between the two is also a transient change in frequency (mostly that of the MK II and of the order of a few tens of μHz per hour at various times throughout the diurnal cycle). I'm currently some 11 hours into another 12 hour run I'd started just after 3 am this morning, after powering the RFS down to try a modification I'd hoped would mitigate the fan vibration issue that caused those rapid phase transients. This is for my own use, namely to see whether reducing the elevation mask from 30 down to 25 degrees in the ZED9FT's configuration would eliminate or at least reduce the weird events seen in my timelapse movies so far. Powering the RFS down for the twenty minutes or so that it had taken me to apply a couple of strips of capton tape to the plenum partition divider to reduce friction in its contact with the LPRO's polystyrene jacket to attenuate the fan vibration effect proved an ineffective strategy so, selecting a low vibration example from my NOS of these fans is now on my to do list. Anyway, I've attached a couple of screenshots (last night's and the latest one taken just now). The RFS trace has leapt some 30ns "backwards" (ahead of the reference in terms of phase) during that 11 hours. However, a not unexpected result after such a brief shutdown and the drift rate looks to have started to slow down as the daily aging drift induced drop in frequency starts to build up. |
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