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

Azelio Boriani azelio.boriani at screen.it
Thu Oct 13 20:49:21 UTC 2011


OK, so the Tbolt hardware resolution is 100pS. If you have a hardware
resolution of 100pS and do an average over the data, yes, you can obtain
greater resolution but your data has to cross the 100pS boundary to have any
variation. If your phase moves under the 100pS window your averaging can
only say that the phase has not crossed the 100pS boundary by an arbitrary
lower resolution obtained with averaging. Of course all must be stable.
Maybe the trick is to use a sampling oscillator that is not so stable so
that it can move the 100pS window to reveal if the phase is near one edge or
the other and "feed the average" with numbers that are not all the same.

On Thu, Oct 13, 2011 at 10:06 PM, WarrenS <warrensjmail-one at yahoo.com>wrote:

> Good ideas, That's more to put on my to do list, But not near the top.
>
> I've got two external Tbolts (one is a loaner) plus an internal one.
> Right now I'm limited because of some long term testing I doing.
>
> Something to be careful about when doing what you suggest is that the two
> Tbolts will not switch birds at the same time, so need to not use that part
> of the data if you want to remove the effect of the GPS. Treat that part
> like outliners.
>
> To check for Tbolt noise floor, Good idea to use just one external one and
> an internal one as long as it has a good low noise Osc in it.
> Can using the 10 MHz output of the internal one to drive the input of the
> external one.
>
> Also to remove as much variation as possible, put BOTH of them in the
> disable mode (but not holdover mode)
> and manually adjust their setting so they both read about the same values
> for their Phase and freq.
>
> Now you're suggesting making a better Tbolt Tic by using two and comparing
> their differences.
> Have to think that over a little, sounds like a good plan, But so far have
> not seen anyone else that will even try it with one.
>
> Thanks,
> I'm now thinking about how to use two external Tbolts in a setup more like
> a DUAL Phase thing.
> The GPS signal can be the Offset osc and therefore will have little effect.
> The GPS will just act as a near zero offset frequency osc, and watching the
> phase differences between the two Tbolts, should work fine.
>
> Thanks, so many fun things still to play with.
>
> ws
>
> *****************
>
> Hi Warren,
>
>  What is not too clear is how much of that is due to the Tbolt engine and
>> how much is the "GPS Reference".
>>
>
> Do you have two working Tbolts with their orginal oscillator removed?
>
>  From what I've seen in my test, a large amount of that noise floor is due
>> to the GPS.
>>
>
> I think a dual Tbolt configuration would eliminate GPS instabilities and
> rely more on the house standard. As proposed in previous email.
>
> --
>
>  Björn
>
> *****************
> snip
>
>
> 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,
>
>    Björn
>
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