[time-nuts] Multiple OCXO (topic changed from E1938A )

[Glen English VK1XX]

Hi  Bob, and Achim . thanks for the comments. I've change the subject 
line to fit more in line we the morphed discussion.

Good discussion, and like Bob said, there will be lots of common mode on 
the GPSs. The diurnal GPS derived clock errors due to the ionosphere are 
well described .   Bob thats a good point about picking and choosing, 
and long term effects.

My initial obs on two devices, tell me there IS  significant 
non-correlated noise between two of them, but this is on low cost GPS  
and also I have not yet established how much noise is purely my edge 
point sampling errors and nothing to do with the actual device, and the 
two in question have different views of the sky....

Acbom, you have clearly thought about this. As for the IDELAYS etc, 
IDELAYS yes have been used for this sort of thing since the mid 90s.  
Enough of them and enough inputs and some known waveform to compensate 
against, and some differential means,  should be enough to mitigate the 
temperature/process effects. If rising and falling edges are worked, 
delay will affect both and compensate. While 1pps source might usually 
be only accurate on one edge, nothing an external ECL / GaAs flip flop 
won't fix to provide 1/2 pps.

One can also use PCB delay...150ps per inch... being careful of FR4 
weave , zig zags etc.....although once the rise time of the signal gets 
amongst the delay we want, thats uncertainty.

**** ***
Assuming we end up with a single, nice clean compensated and as good as 
possible timebase (from 1pps etc) (sounds like your territory, Bob), and
With multiple OCXO ( ALL being simultaneously inter-dependently 
disclipined ) , there may be the opportunity to try different parameters 
(or even algorithms) on the different OCXOs and pick the one with the 
minimum squared error (or something like that) . What might kill that is 
that the OCXOs vary quite alot even on the same model.

The goal of this is

a) to learn something- precision instrumentation is hard.

b) have a 1e-13 accurate long term (weeks on) frequency reference

c) have short term 1000 second stability <= 1e-12

****

glen




On 7/07/2019 6:56 PM, Achim Gratz wrote:
> Glen English VK1XX writes: