[time-nuts] Time Nuts at PTTI this past week

Tom Clark, K3IO K3IO at verizon.net
Tue Dec 12 01:00:02 EST 2006


   [1]SAIDJACK at aol.com wrote:

   Hi Tom,



   how many M12M iLotus samples did you test to find the one with 30ns
   offset? Were these pre-production samples or mass production units?



   How did the other ones perform?



   Seems iLotus may not test/calibrate/inspect as thoroughly as Motorola
   did?



   Thanks,
   Said

   I thought I had noted this in my earlier comments, so I'll try again.
   So far, we have seen only one iLotus M12M sample (and one earlier
   Motorola M12M prototype). The firmware for the Motorola unit reads
   v1.0x6 (like maybe the 6th experimental test version of v.1 ???),
   while the iLotus reads v1.0. If/when we see additional iLotus units,
   we will run them thru the same procedure and see if a pattern emerges.
   Art Sepin (Synergy -- the Motorola & iLotus rep -- see
   [2]http://www.synergy-gps.com/) was at PTTI and we discussed the
   measurements with him. I have reason to believe that he has already
   reported our results to the factory. Rick conveyed the message that he
   (CNS Systems) will be happy to perform the calibrations to get rid of
   the bias if they want.
   The following are my personal comments/observations and should not be
   taken as definitive or authoritarian: I have heard rumors that after
   Motorola "sold" the M12M line to SiRF, most of the Motorola GPS
   technical staff moved to SiRF. SiRF (as I understand it) then licensed
   iLotus to produce the hardware (I guess as a build-to-print task). I
   am unclear on who of the three has retained the rights/details of the
   firmware, so I don't know from whence any future modifications will
   come. The preliminary data sheet that iLotus has at
   [3]http://[4]www.ilotus.com.sg (and that Art has on his web site) says
   "Fully calibrated to UTC at USNO" but I am certain that the M12M has
   never been at USNO; I presume this claim refers to Rick's earlier M12+
   tests.
   Since our entire sample is a universe of one, it is impossible to say
   why the ~30 nsec offset is there. We do believe that the ~5 nsec
   scatter in the M12+ observed in the four-unit 2002 tests came from
   slight differences in the group delay performance of the SAW filter
   that determines the IF response. Since I have never seen a detailed
   block diagram of the M12M innards, I am unable to do any reverse
   engineering to aid in understanding.
   Of course, since the 1PPS epoch can be set in software, any
   manufacturing biases can be easily removed by the user (if 30 nsec is
   actually important!).

References

   1. mailto:SAIDJACK at aol.com
   2. http://www.synergy-gps.com/
   3. http://www.ilotus.com.sg/
   4. http://www.ilotus.com.sg/


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