[time-nuts] Thunderbolt settings -- one more time

[Ulrich Bangert]

Chuck and Dick,

> The T-Bolt is designed to be a turn key system, and is 
> already set up for the best operation the factory knew how to 
> achieve. 

Yes and no! Clearly the factory settings have to be so that a lock of
the pll is possible within a reasonable time, say minutes to hours or
so. With a freshly powered OCXO the initial aging effects can be that
large that really short time constants as the default 100 s of the
Thunderbolt are necessary. 

I attach a measurement that I made on a freshly powered up HP10811 some
years ago. Note: This was by no means a new device but one that had
already thousands of hours lifetime. Clearly any regulation loop will
need short time constants to follow this initial aging. Note that the
aging effects are that big that frequency changes due to diurnal
temperature changes in my flat are not visible! Temperature has
otherwise the biggest impact of all environmental parameters on
oscillator stability.

After some weeks of continuous (!) operation the time constant of the
Thunderbolt loop may be set to higher values. Mine currently runs at
500.0 s. Some tests indicate that the time constant may even be set a
bit higher. I have made experiments on time constants with a number of
different gps receivers and different OCXOs (including RBs). As an
overall result it turned out that TCs > 1500 s are impraticcal in a
normal living environment. With some degrees Centigrade temperature
changes in a typical center European environment along the day that is
the maximum time that allows the loop to follow the temperature changes.
This includes RBs which have an measurable coefficient of temperature
too.

Best regards
Ulrich

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Chuck Harris
> Gesendet: Montag, 1. Dezember 2008 15:03
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Thunderbolt settings -- one more time
> 
> 
> Hi Dick,
> 
> The T-Bolt is designed to be a turn key system, and is 
> already set up for the best operation the factory knew how to 
> achieve. I doubt that anyone has spent much time diddling the 
> time constants.
> 
> -Chuck Harris
> 
> Richard Moore wrote:
> > Dear nuts --
> > 
> > Let me see if I can ask this in a way that will prompt you to supply
> > some input:
> > 
> > What is the maximum Loop time constant the TBolt (or perhaps the
> > TBolt monitor sw) will accept as input?
> > What TCs are you TBolt owners using?
> > 
> > Thx,
> > Dick Moore
> > 
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