[ntp:questions] how do you like the Trimble Resolution T

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Wed Feb 29 08:36:01 UTC 2012

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.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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