Products > Test Equipment
Thunderbolt® E GPS Disciplined Clock
branadic:
Hi to the community,
I have a Thunderbolt® E GPS Disciplined Clock at lab and I'm confused by what I get.
The first module that I received obviously had some defect as amplitude was of compared to datasheet. After some weeks I got a replacement last friday, with amplitude okay right now (1.32Vpp into 50?).
I had run the gpsdo over the last weekend together with Lady Heather's Disciplined Oscillator Control Program. It turned out, that parameters and specifications on real device seems to differ from datasheet and also from what is shown on the web.
First of all the parameters
ParameterMy DeviceUser’s Guide (Factory Default)webTC:60sec10sec100sec.DAMP:1.0001.0001.200GAIN:1.707Hz/V8.830Hz/V-5.000Hz/VINIT: 2.500V2.000V0.000V
Second, after the weekend the stability is also different from what the datasheet suggests.
Maybe someone can help me to understand how to set the oscillator in the right way to get good stability results. Thanks.
branadic
Dr. Frank:
Hi branadic,
I got the Thunderbolt, it contains FW 3.0 and the better OCXO, labelled originally from Trimble.
Description of versions here: http://www.ke5fx.com/tbolt.htm
I have chosen:
TC = 1000sec (before used 500sec)
Damp = 0.7
Gain = -5Hz/V (for the OCXO!!)
Init = 0.787V (dependant on OCXO, and I stored that parameter recently into the TB, to have a faster startup)
Concerning TC and damp, there were long discussions on the time-nuts lists, but less than 100sec was not recommended, afaik. My settings work quite well.
Additionally, related to the location of our house and the surrounding, I have chosen EL (Elevation) = 20°, and AMU = 5.50
The 10MHz Signal is 2.56Vpp @ 50 Ohm, and 5.08V open.
As you see half of my amplitude only, make sure, that there is no hidden 50 Ohm, already..
1pps has TTL level, i.e. 4.96V, 10µs pulse.
Have you already determined and fixed your position by a 24h survey?
That is required, otherwise, you'll get no stable time at all.
(Currently, your coordinates are on the Stuttgart Campus, obviously your lab @ work, nice glass building )
The gain parameter has to fit your type of OCXO, that may also be the root cause of your problems.
You should open your unit and have a look inside, maybe a photo, what's contained.
Frank
- sent from my basement lab -
rf-loop:
--- Quote from: branadic on September 05, 2016, 11:30:56 am ---Hi to the community,
I have a Thunderbolt® E GPS Disciplined Clock at lab and I'm confused by what I get.
The first module that I received obviously had some defect as amplitude was of compared to datasheet. After some weeks I got a replacement last friday, with amplitude okay right now (1.32Vpp into 50?).
--- End quote ---
Bit low but...
In my unit +11dBm (Version 3.0 T.Thunderbolt)
For best result it is best to keep it running example 2-4 weeks continuously. (Inside OCXO XTAL retract and running it back to slow ageing curve take some time)
After then you can adjust better values for discipline.
Also for good result it is best to find your individual unit V/Hz value.
For this you need good frequency counter (abd accuracy not important) then you manually adjust Trimple OCXO frequency control voltage and measure how many Hz it change when you change.
Initial voltage is just voltage what is set for start. It can be what ever but startup/stabilization is more fast if it is near right value. This also change when OCXO ageing go forward.
In my case I use TC 750s and damp 1.1 but I have quite good well aged OCXO and also thermal sensitivity is not so bad.
These default values, example short TC and so on, they are for perhaps better for new units and when purpose is more like time accuracy than frequency. With original settings it accept more frequency error for drive time error out quite fast.
Dr. Frank:
branadic,
I just scanned through time-nuts, and there is a discussion about the new ROHS E type of Thunderbolt.
The new type should be compatible to the old Thunderbolt, but it was a cheaper type, maybe with a different OCXO or piezo.
There was also an old Thunderbolt with FW labelled "E", which may not be mixed up.
So, if you got the new E version directly from Trimble, and not an old TB, that would explain the different TC, damp and gain parameters.
All these are valid and stable, when the GPSDO has a fixed position, and did run for at least 2-3 days.
That's completely sufficient for the OCXO to stabilize, and for the GPS processor to "learn" the behavior of the whole set, concerning hold-over mode, i.e. T.C. (temperature coefficient) of the OCXO, and DAC value.
I think, whenever I let my unit power up again, it will meet the stability / Alan parameters after about 2 days.
It also depends on, whether you monitor the 10MHz, or the 1pps signal. Latter one is more stable, in most cases.
Ah, one further hint: LH probably does not measure the Allan statistics of the TB correctly. That's because she can only compare the OCXO against the jittered GPS signal.
If you want to reconstruct the Allan diagrams coming from Trimble, or from the other Time-Nuts, you better have to measure that, using an external T.I. counter, and a similar or better reference, like another free-running OCXO (in the counter), or a Rb clock. I recommend TimeLab for these measurements, also available from KE5FX.
So you may measure <1e-10 StD @ 1s for the 10MHz already, instead of about 2e-9, what LH usually displays.
Frank
rf-loop:
--- Quote from: Dr. Frank on September 05, 2016, 03:41:10 pm ---branadic,
All these are valid and stable, when the GPSDO has a fixed position, and did run for at least 2-3 days.
That's completely sufficient for the OCXO to stabilize, ...
Frank
--- End quote ---
Yes if think minimum and accept that all are not optimal for start finding optimal parameters. Also ok if think typical Trimble all other instabilities, poor temp stability and cheap OCXO. For normal use 2-3 days is enough. But, very important is that also positioning is well done.
But if talk more deep...
Yes and no. It depends...
Also different xtals are different and so on.
If think ageing curve, retrace etc bit more accurately 2-3 days is "nothing".
But I do not want start more about interesting frequency-nut here (time-nut is boring because after there is more than one clock, no one know exact time)
Who is more intersted can start studying example with this quick lesson:
http://www.oscilent.com/esupport/TechSupport/ReviewPapers/IntroQuartz/vigtoc.htm
There is also sketchy story about XTAL thermal hysteresis and retrace
http://www.oscilent.com/esupport/TechSupport/ReviewPapers/IntroQuartz/vighyst.htm
"Figure 24. Oven-controlled crystal oscillator (OCXO) retrace example, showing that upon restarting the oscillator after a 14 day off-period, the frequency was about 7x10-9 lower than what it was just before turn-off, and that the aging rate had increased significantly upon the restart. About a month elapsed before the pre-turn-off aging rate was reached again. (Figure shows Df/f in parts in 109 vs. time in days.) "
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