[ntp:questions] lots of GPS modules and info at SparkFun
Ron Frazier (NTP)
timekeepingntplist at c3energy.com
Thu Feb 9 09:08:27 UTC 2012
OK, so I'm replying to my own message, what's strange about that? 8-)
VERY preliminary data, after running an hour with my USB GPS without PPS
outputting only GPZDA sentences, I'm getting ~ +/- 5ms peak offsets of
the computer clock vs GPS. I'm liking it so far. It initially looks
more stable than when I was using GPGGA sentences.
On 2/9/2012 2:35 AM, Ron Frazier (NTP) wrote:
> Hi Brent,
> I spent a little while skimming over the 254 PAGE! pdf of the manual
> from the SparkFun website. The device is certainly well documented.
> I couldn't find where they specify the timing relationship you
> specify. That's very interesting if it's consistent. I'm currently
> using a GlobalSat BU-353 USB only GPS, outputting only the GPGGA
> sentence only at 57600 baud. I'm getting ~ +/- 15 ms peak offsets
> between the computer clock and the GPS polling every 8 seconds with
> jitter averaging around 3 ms.
> Based on your note and some data in the Trimble manual, I've reset my
> GPS to output only the GPZDA sentence. I looked at the link below to
> find the mode command to set NTPD to recognize this sentence:
> It turns out mode 8 does the trick, plus the other bits I add to get
> to 57600 baud, so it works out to mode 72. So, the GPS part of my
> ntp.conf is thus:
> server 127.127.20.5 prefer minpoll 3 maxpoll 3 mode 72
> fudge 127.127.20.5 time2 0.3550 refid GPS1
> So, I'm going to let that run a while and see if it's more stable than
> the GPGGA setup.
> On 2/8/2012 6:37 PM, Brent Gordon wrote:
>> One cool thing about the Copernicus, beside the PPS, is that the
>> datasheet specifies the delay from the PPS to start for the ZDA
>> sentence. This means you can use the serial data directly without
>> having to use the PPS. On other GPS units I've looked at, the delay
>> from PPS to ZDA varies greatly (300 ms +/- 150 ms).
>> On 2/8/2012 3:23 PM, Ron Frazier (NTP) wrote:
>>> Hello all,
>>> While researching potential GPS modules to experiment with for PPS
>>> output, I discovered that SparkFun has quite a lot of modules, some
>>> of which have PPS and some of which don't. You can't necessarily
>>> tell from the product page. You have to check the data sheet. You
>>> can go to their website and search for gps. This link should also
>>> work. Just thought I'd pass it along.
>>> Here is one unit which does have PPS but it's not obvious from the
>>> product page. There are others as well.
>>> 12 Channel Copernicus II GPS Receiver - from Trimble -
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