[time-nuts] Common View Tbolt-Tic
warrensjmail-one at yahoo.com
Wed Oct 19 16:09:00 UTC 2011
I think I have confused things by doing two completely different things.
One is how best to make a better Tbolt GPSDO,
the other is how use a Tbolt to make a remote OSC tester.
To do the first, the osc needs to be disciplined slowly,
to do the second, best to do it using the disable mode with no disciplining.
Correct, when the Tbolt is in the disabled mode, using either with it's own
internal or an external Osc, It is just running the osc as a standard OCXO.
But what I'm taking advantage of is that the Tbolt is also recording data
showing what the difference is between that Osc and the GPS signal.
This is the same function any Tic has.
The Tic tester does not change the Osc, it just measures it by comparing the
osc against some other reference.
When the Tbolt is in the disciplined mode, what it does is change the osc by
removing any long term difference between the Osc and the GPS.
This is not so good for comparing oscillators, because ideally they are now
being made equal in the long term.
And correct, when in the TPLL mode, the TBolt 10MHz output has Nothing to do
with it's Osc, It is just showing the GPS noise.
While this allows one to test what the received GPS noise is by using an
external reference and ADEV tester,
it has little or no information about the osc being used and therefore
(mostly) useless for directly comparing the TBolt Osc to the GPS, which is
what is needed to measure common view differences.
Two different functions, two different goals, two different procedures and
two different uses of the Tbolt.
and two different Fun projects
----- Original Message -----
From: "Ed Palmer" Posted
> What do you see when you look at the ADEV of a Tbolt in the Disabled
> state? To me it looks like an ordinary OCXO. In my case, the aging looks
> like about 5E-10 per day. The Tbolt book doesn't say much about the
> Disabled state. Is it possible that the Disabled state means 'Disable the
> GPS and pretend that it's just an OCXO'? If so, this is not the mode you
> want to be in for a Common View test. By comparison, the ADEV of a Tbolt
> in the TPLL mode looks a lot like a bare GPS receiver. Would that work
> better for what you want to do?
> On 10/18/2011 12:32 PM, WarrenS wrote:
>> I'm doing some experiments in hopes of using the TBolt-Tic in a common
>> view configuration to lower the short term noise.
>> That is, instead of comparing a local externally connected Tbolt Osc to
>> the GPS, I want to compare it remotely to one of say Tom's supper
>> H-masers or Cs references.
>> The single view Tbolt-Tic works great using averages of a half day plus
>> to get down to 1e-13, but being nuts I want to do it Faster and better.
>> Test setup:
>> I have three COMPLETELY independent Tbolts running, each with its own
>> LadyHeather monitor.
>> Two of the Tbolts are a couple feet away from each other, the third one
>> is a few hundred miles away.
>> All three are in single satellite mode set to watch the same near
>> overhead satellite.
>> All three of these Tbolt oscillators are capable of short term noise a
>> decade or two better than the short term GPS noise.
>> I also measured the TBolt's engine phase noise to be a decade lower than
>> the short term GPS noise.
>> All three are in disable mode, so that their plotted LH phase noise is
>> for the most part ALL due to the received satellite signal noise.
>> My hope was that there would be a high correlation between the Phase
>> noise of their three Phase plots..
>> What I see is almost no correlation, they are all just doing their own
>> thing with random phase noise of a couple ns.
>> Just to check I tried the same test with a satellite that had an
>> elevation of around 45 deg with the same results.
>> One test I should run is to use the same antenna for two of the Tbolts,
>> But that defeats the whole purpose, which is to be able to compare by way
>> of LadyHeather's remote function, a local Osc to an external Rb or Cs
>> remote reference Osc.
>> Any suggestions?
>> Something is wrong somewhere.
>> Maybe it is that the Tbolt's engine noise is not what I measured it to
>> be, but I have double checked that a couple of different ways.
>> Anyone have personal common view experience comparing Tbolts OR any
>> other thing using GPS.
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