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HP/Symmetricom Z3805A GPS Disciplined Oscillator

Posted on November 22nd, by Shaun Merrigan in Tech, Time and Frequency. Comments Off on HP/Symmetricom Z3805A GPS Disciplined Oscillator

I recently acquired two HP/Symmetricom Z3805A GPS Disciplined Oscillator receiver/clocks.  These units seem to have several different configurations both inside the box and of the box itself, but all appear to have:

  • Two 10Mhz outputs
  • Two 1PPS outputs
  • 24v DC power requirement

Inside the box, I have seen reports of:

  • HP 10811 DOXCO (10Mhz)
  • Symmetricom  DOXCO (5Mhz with a doubler)
  • MTI 260 DOXCO
  • 16 channel GPS receiver (newer builds)
  • 6 channel GPS receiver (older builds)

The box itself can be Samsung rack mount or HP benchtop.   My particular units were older  Samsung rackmount builds, but do have the desirable HP 10811 DOXCO.   Both units had older 6 channel GPS receivers that exhibited the 1024 week GPS rollover bug.  (That is, they displayed a date that was 1024 weeks in the past due to nature of the 10 bit week counter used in the receiver.)  I simply swapped the GPS units for newer ones (pin compatible)  that don’t have that problem.  The replacement Oncore VP GPS receivers are cheap and readily available.

Both the units I purchased were last located in South Korea.  I found this by querying the receivers for their last GPS HOLD location (before I swapped the receivers of course).  I then dropped the coordinates into Google Earth with the following results (the yellow pin gives the geographical position of the Z3805A unit):


Z3805_1 Location Overview Z3805_1 Location Z3805_2 Location Overview Z3805_2 Location Zoom


After cleaning, inspection replacing a smashed LED FP indicator and installing the replacement GPS receivers, I have powered up both units and I will let them run for several months to see if the DOXCOs settle down.   As of this writing, one unit is doing quite well with PU of under 4uS (after about 5 days); the other one has an EFC  error.   Time will tell……


Shaun M.


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