Sunday, October 18, 2015

Measuring Time Takes Time

Here's a little bit of data on the Denuo GPS in a REF-0 during the warm-up period.

Classic "lots of zeros" picture of the REF-0 10MHz output.
Does this shot have much meaning? Not really.

I've been collecting phase data on the REF-0 and Denuo GPS as the pair warms up. My equipment is quite limited, and it's difficult for me to collect useful frequency data in the E-13 range. So I thought I'd just measure the phase difference between the REF-0 PPS and a stock REF-1 with the Oncore GPS. Perhaps measuring the two relative to each other will provide some insight on how a REF-0 performs with a non-timing GPS.

No data was collected for the first two days. I did monitor it casually on the counter, and it was exactly as you'd expect. Lots of big swings and settling.

Below are traces showing T + 48 to 72 hours, and T + 72 to 96 hours.

Notice the "pop" of noise during day three of the warmup.

Make sure to notice the scale when comparing this plot to the first one.

It's difficult to know what's causing what in these plots. The REF-1 has a 15 year old GPS receiver. The REF-0 has a non-timing GPS with no position hold, but great sensitivity. Better references and lots more time will be required to know more.

Though, something interesting happens when you overlay the two plots.

Plots from two consecutive 24 hour periods shown together.

The consistency between them in many spots is easy to see, even though the traces are separated by exactly 24 hours from each other. Especially during the middle of the plot, which would have been the overnight hours, the two follow each other closely. I'm not sure if there's actually anything useful to glean from that.

That's all for now. There's not much data yet, but any comments are welcome. We'll see how the unit does after a week of being on, then a month, then.... 

Thanks for reading!

- Dan W.


  1. Dan

    What is the day/night temperature variation in the lab where this equipment is located? Here in California our summer days can be quite warm and nights very cool. The variation can be over 30 degrees F. I started observing my modified '12 in July and thought I noticed a slight EFC trend that followed my lab temperature. As Fall has come this variation has either disappeared with more modest temperature swings, or maybe the 15 year old (new) oscillator is just settling in?

    1. The temperature fluctuates about 4-5 degrees F throughout the day. It would be a very different story if it were mid-summer or winter. This time of year, I don't have to have the heating or air conditioning on. Those are the worst culprits of course, and cause huge swings in measurements.

      You will notice that about 3/4 of the way through the plots above, there is some noise. That corresponds to the morning hours when the sun is really beating in through the south-facing window. It's likely temperature is part of the reason there.