[time-nuts] LPFRS phase ripple?

Tim Shoppa tshoppa at gmail.com
Thu May 25 07:27:17 EDT 2017

Matthias, are the units all over in the same thermal environment when you test them? 

A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.

Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)

Tim N3QE

> On May 23, 2017, at 3:40 AM, Matthias Jelen <Matthias.Jelen at gmx.de> wrote:
> Hello Time-Nuts,
> i´ve been playing with some Rbs recently.
> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
> Any hints are appreciated.
> Regards,
> Matthias
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