[time-nuts] Tbolt Damping setting

WarrenS warrensjmail-one at yahoo.com
Wed Dec 16 19:33:40 UTC 2009


Peter

>PV) However, I think it would be interesting to at least see the relative 
>differences for one location.
    The  relative difference can be seen in the Green Dac plot, which shows 
the total  PP noise at 50 Sec and slower.
The Dac is scaled to 1e-11 per division, for RMS or ADEV, divide PP by about 
5.
As you pointed out the Tbolt and LH can NOT do 1 sec noise directly without 
an external reference,
BUT by looking at the excess nose that is applied to the DAC, you can see 
what is happening at one sec, or 10 or 100.
Ideally The Dac should not be forced to move at a freq below the TC setting, 
If it does that is added noise.

    By the way,
To force a similar sort of 50 ns sawtooth phase error waveform when using an 
external reference,
Use the Osc phase setting to invert the phase of the Tbolt OSC sync timing.

>PV) Is the oscillator in the Leica significantly worse than that in out 
>Thunderbolts, or could we also benefit from a time-constant of longer than 
>1000 seconds?
    I know little about anything except Tbolts
but If you show me a couple of good plots, with and without GPS control, I 
could probable answer that.


>PV) I will try to find a quiet rubidium
    Depending on what errors you are most concerned with, Phase short term 
or long term , Low tau ADV or High Tau ADV,  (or hold over, yek)
May not even be necessary for it to be a "low noise quiet one"

    Have fun
ws  (in central California)
***********----- Original Message ----- 
From: "Peter Vince" <pvince at theiet.org>
To: "WarrenS" <warrensjmail-one at yahoo.com>; "Discussion of precise time and 
frequency measurement" <time-nuts at febo.com>
Sent: Wednesday, December 16, 2009 4:54 AM
Subject: Re: [time-nuts] Tbolt Damping setting


>> Good points, and You got 4 1/2 out of five correct, Not bad at all.
>
> Ha ha - thank you teacher!
>
> Fairy nuff, yes, your plots show the long-term effects.  I would like
> to know what the best time-constant is to use.  I appreciate that
> everyone's will be different, depending on individual characteristics
> of the Thunderbolts, and also (perhaps more importantly) the aerial
> and its position.  However, I think it would be interesting to at
> least see the relative differences for one location.  I recently
> learnt that our national mapping organisation (The Ordnance Survey)
> average the results from their L1/L2 Leica 1200 system receivers, for
> two hours.  Is the oscillator in the Leica significantly worse than
> that in out Thunderbolts, or could we also benefit from a
> time-constant of longer than 1000 seconds?
>
> I will try to find a quiet rubidium, and do some comparisons against
> that - the results should, at least, be valid out to a few thousand
> seconds.  I also plan to try reducing the signal level threshold (from
> the current 4AMU) as recently suggested, and try to see some
> quantifiable results.
>
>     TTFN,
>
>          Peter Vince  (G8ZZR, London, England) 




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