[time-nuts] Measuring ADEV using TBolt-Tic tester
ws at Yahoo
warrensjmail-one at yahoo.com
Thu Oct 13 10:11:22 UTC 2011
I know very little about the HP58503A. Any chance it is using the old 6
channel Oncore GPS engine?
If it is like the Oncore I tested long ago, that noise was about a decade or
so higher than the Tbolt's phase noise.
Not sure what you can call single-shot resolution. The data is reported with
Pico second resolution.
The cycle to cycle max phase varation, If there is not a satellite change at
the same time, is around 0.4ns max error.
With the very high resolution that is output, averaging provides a lot of
The noise of the Tbolt's freq (PPT) output data measured about ten times
lower than it's phase output data at 1 sec.
How it does it is anyone guess, but looks to be some sort of high speed
averaging going on, taken over a one second time interval.
----- Original Message -----
From: "Azelio Boriani" <azelio.boriani at screen.it
> Your work is very interesting, now I wonder what is the Tbolt
> single-shot resolution? Does the Tbolt use the analog interpolator
> method? I don't have the Tbolt, I have an HP58503A at work as the only
> On 10/13/11, WarrenS <warrensjmail-one at yahoo.com> wrote:
>> John wrote:
>>>I'm curious where you got the noise data for the TBolt GPS engine
>> Besides the measured ADEV plot I posted at
>> Attached is another way I've measured Phase noise of the Tbolt, to
>> optimizing its antenna system.
>> This LH plot shows a total phase noise (GPS, + TBolt + Osc) of 0.087 ns
>> reading to reading variation at one second update, over a time period of
>> minutes using a one second disiplined loop. This is the same as 0.87
>> RMS freq noise if using a 1 second time base.
>> On this test, I set the Tbolt's Time Constant to 1 second and its damping
>> 10. (The Dac gain must be set right on to work right)
>> This causes the Tbolt's discipline loop to correct any phase error due to
>> noise on the very next 1 sec update by stepping the Oscillator's
>> This Is an easy way to measure the reading to reading phase difference
>> just LadyHeather.
>> The data can also be interpreted.as the average RMS frequency variation
>> 1 second, which is approximately equal to the ADEV value at a tau of one
>> second (1e-10).
>> example: If the first phase reading where zero and the next one is +1ns
>> the control loop will change the Osc freq by way of its EFC, by 1e-9 so
>> the very next phase difference is zero again. This makes it into a 1 sec
>> delayed TPLL (Tight Phase Lock Loop).
>> I ran this same test on John's Online Tbolt. Its phase noise measured
>> ns RMS.
>> Most of the difference was caused by satellites switching during the
>> Each switch causes a ns or so noise spike when the number of satellites
>> I also tried several other test including using just one bird with no
>> switching. That was more than twice as noisy depending on which satellite
>> bird I selected.
>> I'd like to see what the Phase noise is of other Tbolts using this same
>> method, especially when using a good choke ring antenna that has a good
>> ws at Yahoo wrote:
>> The noise data is my measured values which I do several different ways.
>> of which are:
>> The GPS engine value was calculated from measuring the UNFILTERED RMS
>> of the freq plot data using LadyHeather, backed up by the independent way
>> looking at the UNFILTERED 1 sec ADEV values obtained when plotting the
>> from that data using an external low noise osc.
>> The other proof that the data is unfiltered was done by black box testing
>> small near instantaneous freq changes of 1e-10 and measuring and how long
>> took the Tbolt plot to settle to the new freq value using different
>> The answer is that it knows the correct freq (within it's nose limits) in
>> the next 1 sec sample period when the filter is turned off.
>> As for the ns phase noise that is the RMS Phase noise value from LH using
>> good LPRO osc with it's Time constant set to many hrs. (Phase correction
>> was 100K sec). The RMS noise value is very insensitive to the filter
>> up to 1000 seconds because most of the phase noise is slower than 1000
>> As far as the 4 to 10 ns day to day USNO data , that has nothing to do
>> sub ns short term noise which I generally limit to more like a few
>> of sampel time, and if there is a satellite change during the test run,
>> I start the test over because I'm looking at GPS engine noise and not the
>> GPS noise causes by changing satellites etc.
>> As far as the 4 to 10 ns over a two day period, that agrees pretty well
>> what I see some times on a bad day.
>> On a good day I can get more like 2 to 3 ns, with a 500 sec filter, on a
>> day up to 5 or 6 ns.
>> For some periods lasting up to 5 to 6 hrs, I've seen numbers as low as
>> ns RMS.
>> From: "John Ackermann N8UR"
>> In that test I was just capturing the ADEV table from the TSC-5120 so
>> have raw phase data.
>> I'm curious where you got the noise data for the TBolt gps engine --
>> far better than I've seen quoted before. The Trimble data sheet that I
>> found specs the system PPS accuracy at 20 nanoseconds one sigma; they
>> separately spec the GPS engine. (The data sheet for the current
>> E data sheet says 15 nanoseconds.)
>> The USNO says that their filtered, linear fit time transfer measurements
>> over a two day period, over the entire constellation, have an RMS
>> of 4 to 10 nanoseconds without SA
>> That may not be apples-to-apples methodology, but it implies that
>> sub-nanosecond results may be difficult to obtain.
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