[time-nuts] Trimble Thunderbolt no longer determines the correct date

Magnus Danielson magnus at rubidium.dyndns.org
Wed Aug 2 20:14:53 EDT 2017


On 07/28/2017 02:01 AM, Attila Kinali wrote:
> On Thu, 27 Jul 2017 17:49:14 -0500
> Didier Juges <shalimr9 at gmail.com> wrote:
>> I cannot imagine a work around since the problem stems from the GPS service
>> only identifying the current date within a particular 1024 weeks epoch
>> unless the government changes the amount of data that is sent over the GPS
>> system. Somebody has to use other method to determine the epoch and add the
>> corresponding offset.
> There is: There is a 13bit week number in message type 10. This gives
> a 157 year span instead of the ~19 years of the 10bit week number.
> This has been part of the GPS standard since IS-GPS-200D which was
> released in 2004. As such I am a little bit surprised that the u-blox
> receivers still don't support this message (the LEA-5 family was released
> in 2007 IIRC). But you can use the UBX RXM-SFRBX  messages to get the
> raw GPS messages and decode them yourself.

Yes, but it is only relevant if you to L2C, on which CNAV is encoded. As 
far as I have seen, there is no support in the L1 C/A NAV, also known as 
LNAV, message for anything but 10 bit GPS-week numbers, which brings 
back the topic.

Now, there is a reason I advocate for L2C and L5 capable receivers, this 
is one of them.

Don't blame receiver vendors for not using L2C CNAV messages when they 
only do L1 C/A receivers.


More information about the time-nuts mailing list