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

WarrenS warrensjmail-one at yahoo.com
Thu Oct 13 14:18:32 EDT 2011


I'll try again.
My last post was completely garbled somewhere along the line.

Using the 1 sec ADEV noise floor from the plot at
http://www.febo.com/pipermail/time-nuts/attachments/20111007/48d1ab68/attachment-0001.gif

This shows the RMS sum of the short term GPS signal's noise Plus the Tbolt
engine, plus the Osc, for the achievable resolution at 1 second.

The "one shot", 1second resolution of the Tbolt's phase data is 100 ps or 
less
The "one shot", 1 second resolution of the Tbolt's PTT detector is 10 ps or 
less

What is not too clear is how much of that is due to the Tbolt engine and how 
much is the "GPS Reference".
>From what I've seen in my test, a large amount of that noise floor is due to 
the GPS.
In these cases the Tbolt's external Osc noise is low enough as not to 
contribute significantly to the RMS sum.

This is not necessarily an equal comparison to your 1 shot numbers,
because the Tbolt is using high speed averaging to get its low "single shot"
1second resolution by averaging over many cycles of a higher frequency.

Using this basic technique and averaging over 10,000 cycles of the 100ns 
10MHz signal,
the "one shot" resolution achieved by the TPLL2.0 is under 10 femtosecond in 
1ms.

ws

*************
From: "Azelio Boriani"

The HP58503A has the Oncore 8-channel GPS receiver. The single-shot
resolution capability is the ability to resolve the time interval
without any averaging. For example, the Fluke/Pendulum PM6681/CNT81
has a 50pS resolution, the HP5370 has 20pS, the Racal Instruments 2351
VXI TIC has 8pS single shot maximum resolution, the Wavecrest SIA3000
signal analyzer has 200femtoS hardware resolution at 3GHz.

****************
On 10/13/11, ws at Yahoo  wrote:
> 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
> benefit.
> 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
>
> *****************
>>From: "Azelio Boriani"
> 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
>> reference.
>>
> **********************





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