Ok, thanks for clarifying. In general the time constant one chooses must reflect both the intrinsic performance of the OCXO (essentially constant) and the realities of GPSDO mechanical, sky-view, and environmental conditions (possibly variable). Disabling an oven during a run is equivalent to a radical change in environment and not re-tuning the loop parameters will lead to sub-optimal or misleading results when plotted.
If you have time, it would be instructive to re-run the experiment. First with double oven enabled and do your best case ws-tuning. Then disable the outer oven and again do a best-case tuning. The phase/freq/adev plots would be revealing, as well as the (major?) difference in optimal tuning values. /tvb (iPhone4) On Jul 14, 2013, at 9:19 PM, "WarrenS" <[email protected]> wrote: > Tom > > My posting and plot was only meant to show the difference in tempcoef between > an undisciplined single and dual oven 10811 osc which in this case is clearly > => 60 to 1. > Your comments bring up a different subject which is who needs it and how > good does a controlled GPSDO oscillator need to be when not in holdover. > > As you know, the purpose of a GPSDO control loop is to make the oscillator's > long term stability relatively un-important. > The longer the measurement time the less important the stability of the > controlled osc is in a GPSDO, and as time increases past the GPSDO control > loop time constant, the osc stability matters less and less > > What you are seeing and saying when analyzing the phase and Freq errors > plots, is closed loop performance. > The phase and freq plots of the dual oven osc would pretty look the same even > if compared with a 'perfect' osc, because the dual osc plots is already near > or at the noise floor of that TBolt setup and antenna. > > One can measure the longer term stability of an oscillator different ways; > 1) Hold the EFC voltage constant and measure the change in frequency or phase > with time. > 2) Measure the scaled EFC change necessary to hold the oscillator's freq or > phase output constant > When done carefully and with the EFC voltage scaled correctly both ways can > give the same answer. > > Answer1) > The way I measured the two tempco's is by measuring the correlation between > the EFC control voltage and the temperature plot > In the case of the single oven osc, the plot gains are set so that when > overlayed the EFC DAC plot looks as close as possible to the temperature plot. > When the plot time is >24 hr and there is good repeatability, the TC is just > the ratio of the two plot gains, i.e theEffective EFC freq change divided by > the delta temp. > In the single oven case DAC plot gain = 1e-10 per division, temp plot gain = > 1.5C per division. Tempco = 1e-10 / 1.5 == 6.7 e-11 / degC. > I did the same thing for the dual oven trace by expanding the gain and zero _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
