[time-nuts] Measuring ADEV using TBolt-Tic tester

bg at lysator.liu.se bg at lysator.liu.se
Thu Oct 13 18:45:00 UTC 2011

Hi Tom,

>> 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.
>> ws
> The short-term frequency values could be aided by carrier phase
> while the longer-term timing from code phase. I am trying to dig
> out the work I did on packets 0x8F-AC and 0x8F-A7 some years
> ago.

I propose to also look at packet 0x5A Raw measurements, especially the
doppler measurement. The Tbolt actually does not output carrier phase
measurements, it gives the related doppler measurement.

Is it established that the 0x8F-AC and A7, 10 MHz and PPS offset
measurements are not the output from some internal filter estimation?

It would be interesting to relate the 0x5A individual doppler measurements
to the individual 0x8F-A7 SV clock biases.

> In those runs I recorded all the raw data from a TBolt (not from
> LH) at the same time as comparing the 10 MHz output against
> a stable reference. That helped separate internal tracking effects
> from actual 10 MHz performance.

I propose an experiment with two Tbolts running from the same antenna and
sharing the same oscillator, ie at least one of the Tbolts modified to
accept external 10MHz. This would take out most/all GPS system errors,
leaving receiver measurement noise.

When speaking of 1-shot resolution I think a dual-Tbolt configuration,
with one driven by the DUT and the other by the house standard, is closer
to a fair comparison with a TIC instrument. Since this configuration will
eliminate the GPS system and propagation errors and the TIC is always
limited by the house standard.

Does anyone have two working Tbolts modified for external oscillator
available for testing?  I have one Tbolt and a loaner unit from a friend.
I am not very keen on modifying the two I have in my lab right now.

kind regards,


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