> Should the multiplier value be +1.0000000000000e-09 or +1.0000000000000e-10?

I worked with Chris off-list on this one. It turns out he was measuring his new 
PRS10 and trying to match his ADEV plots against the published plots from SRS. 
Hence the request about 1e-9 (which is ppb and should be correct) and 1e-10 
(which is not ppb, but seems to give a much closer match of the plots). It's an 
interesting mystery and I'm glad he posted his question. He's new to the list, 
but clearly has gone well down the time nuts path already.

He was using Heather to monitor the PRS10, extracted the "FC" column from the 
log file, and used Stable32 to scale and plot the ADEV. Can you spot the 
problem?

The integer FC (Frequency Control) values from the PRS10 is a pair of DAC 
settings; the DAC used to steer the internal OCXO to the rubidium resonance. 
Heather scales these two numbers by 1.5e-9 and 1.5e-12 (per the manual) [1] and 
then scales them by 1e9 (so they logged as ppb). Stable32 (or TimeLab) then has 
to unscale them back by 1e-9. So far so good.

But the actual problem is that the FC value is *not* a measurement of PRS10 
performance. It's simply telemetry that shows how the DAC is operating; how 
much steering the OCXO needs to generate a Rb-locked 10 MHz output. In order to 
actually measure the output of a PRS10 one needs a rather high-res counter as 
well as a better-than-PRS10 frequency standard as a reference. A PRS10 can't 
measure itself, and Heather is a reporting tool not a measurement tool.

I'm guessing that the reason scaling by 1e-10 looked closer to spec is that by 
tau 100 s the Rb is about an order of magnitude better than the OCXO. But let's 
find out for sure.

Two questions for time-nuts:

1) Do any of you have log files of FC values from your PRS10? I'd like to 
compare yours with Chris's to see if they are in the same ballpark. A couple of 
hours or a day is all that's needed. Either raw ascii from the PRS10 itself or 
processed values via Heather is ok.

2) Have any of you ever logged the FC values while at the same time taken 
precision measurements of PRS10 output phase? I ask because that would allow 
one to sort of back out the DAC adjustments and make ADEV plots of both the 
OCXO and the Rb. It would then nicely show the effect of the Rb disciplining 
the OCXO, similar to how we make plots of GPS disciplining a OCXO. [2].

Thanks,
/tvb

[1] https://www.thinksrs.com/downloads/pdfs/manuals/PRS10m.pdf
[2] http://www.leapsecond.com/pages/gpsdo/


----- Original Message ----- 
From: "Chris Burford" <cburfo...@austin.rr.com>
To: <time-nuts@lists.febo.com>
Sent: Wednesday, August 08, 2018 7:10 AM
Subject: [time-nuts] Stable32 Input (Multiplier)


> I'm using Lady Heather to write data from an RFS. In looking at the data file 
> it appears the values are written as ppb. My question is how to best 
> accommodate this with the correct Stable32 multiplier value. Should the 
> multiplier value be +1.0000000000000e-09 or +1.0000000000000e-10?
> 
> It seems I have thoroughly confused myself as to which value will scale the 
> data properly.
> 



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