[time-nuts] S/A, Receiver Glitches, Y2K etc

Tom Clark, K3IO (ex W3IWI) K3IO at verizon.net
Sun Mar 12 18:10:19 EST 2006

   Don did not mention which basic receiver is inside his AUTEC box. Some
   receivers do exhibit glitches. Some of these are documented in my 2000
   ION paper Low-cost, High Accuracy GPS Timing available on
   [1]http://gpstime.com. You might find some of the Timing for VLBI
   tutorials to be of some interest also. The ONCORE v.3 firmware is
   known to have glitches 50 nsec glitches every 19.5 nsec.
   Also, S/A has been turned off since May, 2000 and the US Gov't has
   made a commitment that it will stay off.
   The GPS "Y2K" problem occurred in August 1999. The timing broadcast is
   in terms of elapsed seconds since Jan.6 1980. The seconds are sent as
   a 20-bit word in order to accommodate 604800 seconds per week, and a
   10-bit (range=0-1023) week counter from 1980. The 10-bit counter
   overflowed 1023 weeks after 1980 in Aug, 2000. Some manufacturers
   started their conversion algorithm later (like when their first
   receiver was delivered), and their week ambiguity occurred later. And
   there may be some manufacturers that have receivers that will glitch
   at a later day -- who knows? In general these glitches happen at the
   start of a new GPS week late Saturday nite.
   Regards, Tom


   1. http://gpstime.com/

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