[time-nuts] TrueTime XL-DC Problems

Björn Gabrielsson bg at lysator.liu.se
Tue Aug 5 13:33:24 EDT 2008

Hi Herb,

I am not familiar with the details of the XL-DC. So if you get more
informed suggestions, try them first... 

However your GPS receiver may be bitten by the GPS week rollower



It is now GPS WK 1491 (467+1024). The GPS receiver firmware could have
been "week-rollover-safe" by adding 1023 to "small" week numbers. 

Try to identify the GPS receiver model and search information on that
particular unit.

Can you eavesdrop on the GPS module? (Easier if it uses an ASCII NMEA
message, more work if its a binary protocol). Check that it does output
a valid date.

Your model seems to be current with the manufacturer. Have you checked
for the latest firmware?

The DAC seem to move in the middle of the range. But have you double
checked that the 10MHz output is as good as the unit says?

Good Luck!



On Tue, 2008-08-05 at 11:30 -0400, MENSA999 wrote:
> This is a long shot but I am hoping that someone might be able to give
> me some Hints as to a problem that I am having with a Used 151-601
> XL-DC Receiver that I recently purchased. When I first fired it up it
> showed a date of 1990 so I updated the Date to the current one and
> then went through a 24 hour Auto Mode set up. Once the receiver went
> into Time mode at the end of set up. I pushed the Location button and
> noted A good Lat, Lon and elevation had been established. The LCD was
> showing 3D for the most part and 5 or 6 SAT PRN's. Looking at Osc
> Stats I see Offsets ranging from the 10 -10 to 10 -12, Drift 10-08 to
> 10-09, Phase 10-08 to 10-10 and DAC ranging very slowly from 15950 up
> to 16400 or so. Now the bad news after days of operation I am still
> showing GPS Unlocked,  Position,  Time Unknown (Even though a Lat, Lon
> had been established and UTC had been added through a Function
> command), Time Error and Acquisition Error ; when I do a F73 "Show
> Faults" . I seem to be acquiring the satellites but not decoding their
> full message. I am not sure if this is due to a mistake I am making or
> a receiver failure. 
> Any suggestions that anyone can give would be ever so greatly
> appreciated for I am at a loss and so far my web searches have been
> fruitless. Thank you all for your consideration in this.....
> Herb Belin
> Mensa999 at aol.com  or  413 530 0048
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