[time-nuts] FE-5680 frequency jump

Attila Kinali attila at kinali.ch
Mon Apr 1 19:12:49 EDT 2013


On Mon, 01 Apr 2013 23:57:48 +0200
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> On 04/01/2013 10:06 PM, Bob Quenelle wrote:
> > I’ve been running an FE-5680 for maybe a total of 50 hours over the last
> > several months.  I found that an offset setting of 180 made it track GPS and
> > (previously-set) LPRO-101 10 MHz signals.  Even with power cycling, after
> > about 1/2 hour, with an offset setting of 180 the FE-5680 was stable.  The
> > last time I turned on the FE-5680, it drifted with a setting of 180 and
> > needed a new setting of –415 to track the other signals.  That’s a change of
> > 595 counts and with a resolution of 6.8 uHz per count, a frequency change of
> > 4 mHz (0.004 Hz) and 0.4 ppb.   Operation at the new setting is stable for
> > now.  The lock signal indicates lock and the power supply voltage is still
> > 15V.  I haven’t checked lamp voltage or VCXO voltage as that requires
> >  opening the case.
>
> How long have it been turned on since last power-up?
> 
> Let it sit for a day at least.
> 
> I've found that it is easy to be in too much hurry to judge the 
> situation and trim things efter power-up. The crystal oscillator just 
> doesn't get the time to settle in.

That might be indeed the case. Figure 3 in [1] gives "quite high"
frequency aging differences after switch on and long run time.



			Attila Kinali

[1] http://www.pi5.uni-stuttgart.de/common/show_file.php/lectures/100/blaetter/The%20Rubidium%20Clock%20and%20Basic%20Research.pdf

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