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

WarrenS warrensjmail-one at yahoo.com
Thu Oct 13 16:06:40 EDT 2011


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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