[time-nuts] Z3801A going into Holdover

[Tom Van Baak]

Dan,

I hate to speculate but it's really odd that more than one person is 
reporting EFC issues with the Z3801A this week. I wonder if it's a bug 
in the Motorola Oncore; the OEM GPS receiver used in the Z3801A (and 
other early hp GPSDO). Two events have happened recently:

1) There was a GPS WNRO in April 2019, so Oncore dates will be wrong. 
But, like the rollover in August 1999, this shouldn't cause a GPSDO to 
go crazy.

2) More interesting, as of June 16, it's been 128 weeks since the 
previous leap second. There were reports of some aircraft GPS receivers 
losing lock from June 9 to June 16 due to an obscure bug in certain GPS 
receivers. It's related to leap seconds and 8-bit week numbers (127 + 1 
is -1 not 128).

In theory this shouldn't cause a GPSDO any trouble, but I know that a 
vaguely similar 8-bit problem occurred with the Oncore VP back in 2003. See:

http://leapsecond.com/notes/leapsec256.htm

If anyone happens to have a binary log from an Oncore VP or UT for the 
past week or two, please let me know.

Thanks,
/tvb


On 6/20/2019 10:05 AM, Dan Rae via time-nuts wrote:
> I have an elderly 3801A with some 182,000 hours on the clock, which if 
> my arithmetic is correct means over twenty years of operation.  Since 
> it has a well aged and remarkably stable OCXO I would like to keep it 
> going if possible.  Recently it has been going into Holdover and 
> staying there for no reason that I can see, it is fed from the same 
> antenna / splitter amp combination with a good sky view as eight other 
> GPSDOs here.  LH reports as good a signal strength on it as any of the 
> others.  A Cold Reset gets it going again.
>
> Does anyone know if a more modern receiver can be fitted in place of 
> the existing VP6?  Is it likely to be a Rx problem anyway?
>
> I'm running LH at the moment and will try to capture a screen when it 
> next goes into Holdover to see if that gives me any clues.
>
> Thanks for any advice!
>
> Dan
>
>
>
>
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