[time-nuts] Home made GPS disciplined atomic clock

[Francesco Ledda]

The challenge is to detect a failure of the GPS source (LOS) before the DPLL
moves the OCXO.

I used to design Stratum clocks for a large telecom company, and I used
several trick do detect a phase ramp on the digital phase detector; this was
used to declare a probable bad source.  At that point, we halted the
movement of the DPLL and observed the phase detector activity. We had two
DPLLs, and if both detected a phase ramp, we declared the source bad.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Tom Van Baak
Sent: Sunday, January 25, 2009 11:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Home made GPS disciplined atomic clock


> I think that it should be a much better (in theory) than OCXO which
> comes short therm stability (what I'm actually seeking for). It should
> be much more accurate with long holdovers also.

Right, it all depends on what stability you're after. The OCXO
will have much better short-term stability than the LPRO -- the
LPRO is close to ten times worse. So do not replace the TBolt
OCXO with a LPRO if short-term stability is your goal. See:

TBolt OCXO plots:
http://www.leapsecond.com/pages/gpsdo/
http://www.leapsecond.com/pages/tbolt-tc/
LPRO plots:
http://www.leapsecond.com/museum/lpro/

However, if long-term, GPS-unlocked, holdover performance
is the goal, then using a Rb would make a good choice.

> This is very simple modification by the way. Infact my original plan was
> to use the 1PPS to synchronize the LPRO C-field with separate control
> ...

See John Miles work to replace the Thunderbolt OCXO:
http://www.thegleam.com/ke5fx/tbolt.htm

/tvb

> Here's a link for the log:
> http://www.amigazone.fi/files/gpsdo/tbolt-lpro-test.log
> (Log format: TOW, PPS offset, DAC voltage, Disciplining mode & activity)

I'll have a look at this; but it's not accessible for some reason.

/tvb



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