Said at JLT isn't currently on the list so I'll forward his input: ---------------------- . It looks like you are measuring the output of the OCXO or TCXO inside the LN Rb. That unit has a tempco spec of 20ppb over its operating temperature, the Rubidium is much much better of course (up to 0.07ppb on the Ultimate unit!). With a spec of 20ppb, the unit will react to sudden and large temp changes.
. The OCXO does get disciplined by the Rubidium, however the time constant is user-selectable, and thus the speed it takes to recover frequency/phase errors after a temperature change depends on the user settings inside the unit. Time constants can vary up to many 100's of seconds, and this may be the reason why your unit reacts the way it does . These units are designed to provide down to 4E-013 performance from 0.1s to 10+ seconds just sitting on a bench typically. You cannot achieve that if you thermal-shock this unit due to the single oven OCXO inside. However we do achieve that performance just sitting on a bench here without any special shielding, with normal AC cycling. So something is potentially not working properly or not set up correctly with your unit. To debug, we would need to get a GPSCon log file, see below. . If you require very stable frequency/phase over temperature, then you should use the direct ("unfiltered") 10MHz and 1PPS outputs from the Rubidium oscillator, and not their filtered versions from the SOCXO. The manual describes how to switch to the Rb direct 1PPS and 10MHz outputs via the command line. You should get up to 0.07ppb over temperature on those outputs if you have the Ultimate version and the unit is properly configured. . If you ordered the lowest cost version, then you only have a good TCXO as the noise filter. That has a tempco of 75ppb(!) but the time constants are only 10's of seconds for that unit. It is only used to improve the phase-noise of the Rubidium. Please put this into perspective: the TCXO has > 1070x the thermal sensitivity of the Ultimate Rubidium oscillator itself . Please provide log files using the free JLT GPSCon application that can be downloaded from the JLT website, otherwise it is very hard to figure out what is happening Unfortunately there are no DOCXO's on the market that would a) fit into the 1.00 inch high enclosure, and b) have even anywhere near as good an ADEV or Phase Noise performance of the SOCXO we use in the LN Rb module. It's simply physics. We opted for the incredible stability and phase noise performance this oscillator provides, but that does have drawbacks. If we had used a DOCXO, the thermal stability would have been 100x better than the 20ppb we have now, however the ADEV and Phase noise would have been an order of magnitude and more than 10dB worse. So in summary, if you need great phase and frequency performance over thermal shocks, then please use the unfiltered, Rb-direct output option, that is why they are available via software command. Hope that makes sense, Said ---------------------- -- john, KE5FX Miles Design LLC > -----Original Message----- > From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of > AC0XU (Jim) > Sent: Sunday, February 03, 2019 6:52 PM > To: time-nuts@lists.febo.com > Subject: [time-nuts] Behavior of a disciplined rubidium oscillator? > > Time Nuts- > > Here is a reference to the LN RB spec sheet: > > http://jackson-labs.com/index.php/products/ln_rubidium > > It doesn't seem to give a temperature coefficient. It does say the baseplate > temp range is -20 to +70C. > > Again, my issue is that a slight change in temperature leads to a huge, if > short term, time shift. That seems to me like very strange behavior. I will > contact JL to see if they have an explanation. It does suggest that the unit > should be installed in a temperature-controlled enclosure. > > Jim _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.