[time-nuts] Datum 9390 Problems

Magnus Danielson magnus at rubidium.dyndns.org
Mon Mar 23 22:23:35 UTC 2009


David,

David I. Emery skrev:
> On Mon, Mar 23, 2009 at 04:17:00PM -0400, phil wrote:
>> Firmware for that vintage is out of the question now. It is my understanding 
>> that newer receiver boards solved that issue. My question, could some newer 
>> generic receiver module be programmed/interfaced to replace that board? I 
>> don't have a component level manual on that receiver.
> 
> 
> 	I have a 9390 with Rb - currently in deep retirement - that I
> acquired in 2000.   It locked OK after I repaired the 16.368 MHz oscillator
> lock circuit, but had the rollover date problem.

What magical GPS week number did we just hit?
http://www.ngs.noaa.gov/CORS/Gpscal.html

The time of failure matches the entering of GPS week 1524. This is an 
interesting number as it is exactly 1024 + 500. 500 seems like an fairly 
arbitrary GPS week number to use as a base number. It matches... 1989-08-06:
http://csrc.ucsd.edu/scripts/convertDate.cgi?time=0500+0

So the magic GPS week roll-over bias is now known for these.

> 	I eventually was given a small PIC microcontroller based adapter
> card from a defunct 9390 someone else owned that went between the Trimble
> GPS board and the Datum mother board and fiddled the serial data
> messages from the GPS to correct the GPS date (as I remember it, it
> added the leading 1024 bit in a 16 bit field). This corrected the date
> so it read correctly.
> 
> 	This Datum mini board was apparently at least one of the fixes
> that Datum provided customers for the GPS date rollover bug - there may
> also have been some updated firmware for the motherboard, I forget.

Strange option to make a separate board rather than modify the firmware.

> 	I did disassemble the PIC code, but what I did with the results
> I forget... other than decide what the board did to the data stream.
> 
> 	I did have a copy of the schematic and a user manual for the Datum
> 9390 I got from Symetricomm/Datum - this definitely did NOT include much
> info on the Trimble GPS board and as I remember it the manual didn't
> match the firmware I had all that well nor did the schematic match
> the hardware I had exactly either.

Wohooo!

>> I too have a couple of those units that we use simply for the disciplined 
>> rubidium 10 meg out even though the week and year is and has been off for 
>> some time.
>> Phil
> 
> 	I guess it is time to look up the GPS date in weeks and see how
> close to the next rollover it is...
> 

Can be any week now... but week 1536 (1024 + 512) seems like a likely 
arbitrary week like anyone...

Maybe it is time for me to get a GPS L1 tester...

Cheers,
Magnus




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