Ron Frazier (NTP) wrote:
Hi all,
Is anyone using the Trimble Resolution T GPS for timing? I was looking
at an ad for one on ebay. For my purposes, any accuracy under 1 ms is
great. I don't have to have 15 ns. Of course, smaller numbers are always
better. Is this device hard to setup and program for PPS and use with
NTPD? What accessories are needed?
This is what the ad says is included:
quote on ->
The Resolution T Starter Kit provides everything you need to start
integrating the module into your application. The kit includes an
active, external 5-VDC Bullet-style antenna
<http://www.ioffer.com/info/redirect_notice?url=http%3A//item.taobao.com/auction/item_detail.jhtml%3Fitem_id%3D9a519ec253fb6de5012d1e206938da00%26x_id%3D0db1%23>,
50 feet of RG-59 cable, and an AC/DC power adapter. The starter kit
enclosure includes a mother board that provides serial output, and a
serial interface cable. A reference manual and monitor programs are
provided on CD-ROM.
I could not get to that taobao link...
<- quote off
I notice the unit only tracks 12 satellites and has 141 dbm sensitivity,
which seems to be less than some units. Is that a problem?
Should not be as long as you can get an outside antenna location.
Finally, what is sawtooth correction?
Most GPS chipsets run off a 10 MHz clock, which means that the best they
can do is to locate the actual PPS edge on the nearest 100 ns boundary,
i.e. you'll get an error of +/- 50 ns which the gps knows about.
Timing gpss like the Oncore UT+ sends the known PPS offset as part of
the serial timestream, telling NTPD (or any other recipient) how
early/late the pulse actually did arrive.
This is nice to have if you also have a stabilized clock source for your
motherboard, along with hw to detect and measure the interrupt latency,
i.e. the time between the PPS pulse and when the OS driver wakes up and
notices it.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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