[time-nuts] Warped back to 1993

[Magnus Danielson]

On 08/11/2013 05:18 AM, Mark C. Stephens wrote:
> Okay this is what worked for me:
>
> 1. Removed power and antenna.
> 2. apply power with no antenna.
> 3. send :GPS:INIT:DATE 2007,08,11
> 4. plug antenna back in.
>
> For some reason if I used the correct date, the Z3815A warped back to 1993.
>
> But I am curious why did this happen today?
GPS weeks begin on sundays. Today is first day of week 1753:

http://csrc.ucsd.edu/scripts/convertDate.cgi?time=2013+08+11

Going back 1024 days gives you week 729 day 0, which occurs on 1993 12 26:
http://csrc.ucsd.edu/scripts/convertDate.cgi?time=1993+12+26

A simple way to compensate for the lack of bits is to assume wrapping
occurs, so week numbers lower than som value actually lacks 1024 weeks.
A trivial code like this fixes this:

if (week < 729)
    week += 1024;

Brilliant until you reach week 1753.

I've seen this happen at 500 and 512.

Cheers,
Magnus

>
>
> --marki
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Mark C. Stephens
> Sent: Sunday, 11 August 2013 1:06 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Warped back to 1993
>
> Hal, I can't get it to take, I keep getting E-350 and the time does not change.
> Did you unplug the antenna or anything while you changed date?
>
>
>
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Hal Murray
> Sent: Sunday, 11 August 2013 12:54 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Warped back to 1993
>
>
> marks at non-stop.com.au said:
>> A Z3805A, a Z3815A and 58534A integrated timing antenna all think it's 
>> 26 Dec 1993.
>> What happened?! _______________________________________________
> Is that off by 1024 weeks?  (Looks close, but I haven't checked the details.)
>
> There is a week field in the GPS data stream.  It's only 10 bits.
>
> I had that problem on a Z3801A.  It did the right thing after I told it the date.
>   :GPS:INIT:DATE 2011,12,26
>
>
>