USGlobalSat GPS Forums

Please login or register.

Login with username, password and session length
Advanced search  

News:

Pages: [1]   Go Down

Author Topic: bu-353 as time source  (Read 507 times)

pmuyter2014

  • Newbie
  • Karma: 0
  • Offline Offline
  • Posts: 1
bu-353 as time source
« on: January 14, 2014, 04:06:57 am »

Hi,

I use many BU-353's (sirf iii) as time source, in their out of the box mode, at fixed locations, each one for a different computer, but I have several problems :

1) I use the time and date from the GPRMC message, and relate it to the timestamp of the '$' character in the previous GPGGA message, which has the same time information, using a program in the highest priority on my linux boxes.  Is that the right way to do ?

2) I have noticed that the messages do not come regularly every second; they are frequently delayed, and sometimes are even delayed by many seconds.

3) When I take only the time given by the gps receiver for messages that came "in time", and compare it to a stable ntp source, I notice that the difference decreases over time, and then is reset to an initial value, then decreases over time with the same slope, then is reset to the same initial value and so on, giving a sawteeth graph, with a quasi-constant period.  Each gps receiver exhibits the same behaviour, but with a different period.  The time jump at the reset seems to be the same for all gps receivers: about 100 ms.

What can I do, without changing the hardware, to get a better time accuracy and stability ?

Thanks in advance
Logged

USG_TECH9

  • Administrator
  • Full Member
  • *****
  • Karma: 0
  • Offline Offline
  • Posts: 120
    • USGlobalSat
Re: bu-353 as time source
« Reply #1 on: January 21, 2014, 12:55:12 pm »

Hello pmuyter2014,

I'm not that familiar with how to use a BU-353 as a time source, but I can try and help resolve your issues.

Quote
1) I use the time and date from the GPRMC message, and relate it to the timestamp of the '$' character in the previous GPGGA message, which has the same time information, using a program in the highest priority on my linux boxes.  Is that the right way to do ?
That sounds like it should work. Have you tried referencing just one NMEA sentence instead of looking at two different ones?

Quote
2) I have noticed that the messages do not come regularly every second; they are frequently delayed, and sometimes are even delayed by many seconds.
Each NMEA sentence will output every 1 second. For example, the RMC sentence will output every 1 second and every GGA sentence will output every 1 second, but they output every 1 second independently from each other. At least that's how I understand it. Are you seeing something else?

Quote
3) When I take only the time given by the gps receiver for messages that came "in time", and compare it to a stable ntp source, I notice that the difference decreases over time, and then is reset to an initial value, then decreases over time with the same slope, then is reset to the same initial value and so on, giving a sawteeth graph, with a quasi-constant period.  Each gps receiver exhibits the same behaviour, but with a different period.  The time jump at the reset seems to be the same for all gps receivers: about 100 ms.
I'm not sure exactly what kind of time accuracy you can get out of a device like the BU-353. But from my understanding, the BU-353 is not designed for precise time accuracy. If you're looking for more precise time, then I would suggest a device like the MR-350P-S4, which has a 1PPS output synchronized to GPS time: http://www.usglobalsat.com/p-713-mr-350p-s4-bulkhead.aspx

Let me know if you have any further questions. Thanks.

-Jesse
Logged

redapplejoe

  • Regular Members
  • *
  • Karma: 0
  • Offline Offline
  • Posts: 9
Re: bu-353 as time source
« Reply #2 on: April 21, 2014, 08:22:59 am »

I have been using the MR-350P with a precision video time inserter.  The replacement for that, the MR-350P-S4, gives me errors, possibly because the firmware is a new version.  Can the firmware be changed back to the earlier version?
Logged
Pages: [1]   Go Up
 

Page created in 0.204 seconds with 19 queries.