Re: [ntp:questions] Offset Average (Normal)?

[Ron Frazier (NTP)]

Turning off all sentences other than GPGGA will certainly reduce jitter 
in the NMEA data.  It may help with the timing of the PPS, but I don't know.

Also, take the polling interval to the GPS all the way to 8 seconds 
(minpoll 3).  That will allow minimum drift time between samples.  You 
can raise the polling interval again once you've verified that the GPS 
is working OK.

If you're using the NMEA driver, you can use a fudge time1 parameter to 
adjust the PPS offset, but I'm not sure exactly how that works.

http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html

Sincerely,

Ron


On 3/12/2012 11:21 PM, Alby VA wrote:
On Mar 12, 11:09 pm, Bruce Lilly<bruce.li...@gmail.com>  wrote:
   
On Mon, 12 Mar 2012 18:27:52 -0700, Alby VA wrote:
     
  My whole setup isn't anything special. SureGPS is modified so you get
PPS.
RS232 cable to COM1 on a FreeBSD box. USB providing power. And several
NIST/USNO servers in ntp.conf for reference.
       
"COM1" on FreeBSD?!?  Are you sure?

If really a tty, is it a normal implementation or via a USB conversion?

For USB, a 1 ms pk-pk sawtooth is the best one can achieve.
     


  The USB is just providing power to the SureGPS. The RS232 is handing
the
Rx/Tx/PPS and such. Everything is coming in on /dev/cuau0.


FYI:
------
godzilla# cat /dev/cuau0
$GPGGA,032052.000,3903.1188,N,07729.1077,W,
1,10,0.85,104.9,M,-33.4,M,,*52

$GPGSA,M,3,06,23,07,03,13,08,11,01,28,19,,,1.60,0.85,1.35*09

$GPGSV,3,1,12,19,76,085,31,07,69,315,42,03,41,050,31,13,38,218,30*77

$GPGSV,3,2,12,11,32,160,35,08,31,315,22,06,28,048,30,16,19,074,*79

$GPGSV,3,3,12,23,17,193,29,01,12,165,30,28,09,272,27,43,,,*48

$GPRMC,032052.000,A,3903.1188,N,07729.1077,W,0.03,203.72,130312,,,A*7C

$GPGGA,032053.000,3903.1188,N,07729.1077,W,
1,10,0.85,104.9,M,-33.4,M,,*53

$GPGSA,M,3,06,23,07,03,13,08,11,01,28,19,,,1.60,0.85,1.35*09

$GPGSV,3,1,12,19,76,085,31,07,69,315,42,03,41,050,31,13,38,218,30*77

$GPGSV,3,2,12,11,32,160,35,08,31,315,23,06,28,048,30,16,19,074,*78

$GPGSV,3,3,12,23,17,193,29,01,12,165,30,28,09,272,27,43,,,*48

$GPRMC,032053.000,A,3903.1188,N,07729.1077,W,0.03,203.72,130312,,,A*7D

$GPGGA,032054.000,3903.1188,N,07729.1077,W,
1,10,0.85,104.9,M,-33.4,M,,*54

$GPGSA,M,3,06,23,07,03,13,08,11,01,28,19,,,1.60,0.85,1.35*09

$GPGSV,3,1,12,19,76,085,31,07,69,315,42,03,41,050,31,13,38,218,30*77

$GPGSV,3,2,12,11,32,160,35,08,31,315,22,06,28,048,30,16,19,074,*79

$GPGSV,3,3,12,23,17,193,29,01,12,165,30,28,09,272,26,45,,,*4F

$GPRMC,032054.000,A,3903.1188,N,07729.1077,W,0.08,203.72,130312,,,A*71

^C

   

--

(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com

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