Bruce Douglas wrote:
> There is a new product out which makes even greater claims:
>=20
> http://www.ambient.de/Trilevel_lockit_instWS.pdf
>=20
> This is a relevant quote from that fairly large pdf:
>=20
> "The Lockit box 202C and 202T produce timecode at under one frame in 24
> hours drift. Video sync is locked to that. Accuracies between boxes are
> better than 0.5 ppm from minus 10 to plus 40 degree C (14F-104F).
> Calibration will hold to under one ppm for over one year. The Lockit bo=
x
> is unique because its crystal can be calibrated in the field to better
> than 0.2 PPM to match other generators."
>=20
> I'm really curious as to how they would achieve that much precision
> in a small field unit.

VCXO or TCXO (temp comp'd crystal osc), with lookup table to provide
control voltage changes (or divisor tweaking) for temperature and long=20
term aging effects.

The 'can be calibrated in the field' suggests VCXO since all that would
be needed is a small shift in the VCO bias to effect a 'calibration'.

http://www.wenzel.com/documents/vcxo.html

Very good Circuit Cellar article on keeping time
http://www.jameco.com/Jameco/images/cc-images/novacek-119.pdf

http://www.mouser.com/catalog/supplier/fox.pdf age 73+ has good info

More than you ever wanted to know about crystals
http://www.oscilent.com/esupport/TechSupport/ReviewPapers/QuartzControl/f=
cdevices.PDF

Microcontrollers have helped immensely in improving the long term stabili=
ty of
crystal osc's (note, I didn't say 'phase noise')..

> Robert Rolf wrote:
>  > http://www.nagrausa.com/NAGRA_IV.htm
>  > "Time code generator stability:
>  >
>  > +/- 1 ppm from -10 to +40=B0 C corresponding to a variation
>  > ^^^^^^^^^^
>  > of +/- 1 frame in 9 hours of operation at 30fps or in 11 hours
>  > at 25fps (+/- 2 ppm from -10 to +60=B0 C) "

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