[time-nuts] Surplus Rubidium Oscillator Frequency Spread

Skip Withrow skip.withrow at gmail.com
Thu Aug 27 22:37:52 EDT 2015

Hello time-nuts,

As an experiment I took 10 FEI FE-5650A rubidium oscillators and measured
their frequency error (units were chosen randomly).  These were 15MHz units
taken directly off the telecom cards with no modifications.  These units
never went to China, and are pulls from working systems.  Each unit was
allowed to warmup for a couple of hours before the measurement was made.

Results were:
Unit #       Date Code      Error
301302     0716               -2.87 x 10E-10
C312570   0839              +4.16 x 10E-11
79119       0701               -1.01 x 10E-10
C312324   0812               -2.54 x 10E-10
69008       0450               -2.52 x 10E-10
60495       0352               -6.05 x 10E-10
78894       0651               -4.30 x 10E-11
79287       0701               -2.77 x 10E-10
71379       0523               -1.80 x 10E-10
78871       0651               -8.58 x 10E-10

Date code is YYWW.  The units with a 'C' in front are after production was
moved to China.

All but 1 of the units ran slow (my reference was a Trimble GPSTM, locked
to GPS, so should be within a couple parts in 10E-12).  I doubt that FEI's
reference was off by a couple parts in 10E-10, so my conclusion is that
they tend to age slower while in service (they are disciplined to GPS in
the application anyway).

These oscillators can be stepped by 6.8 x 10E-13 via digital control.  When
modified by us at RDR we set them +/-2x10E-11 (for a 00 00 00 00 control
word).  It would be interesting to know how many hours are on each of the
test units, but I know of no way to obtain that information (unless it is
part of the secret information that be read out of the unit).

Skip Withrow

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