[time-nuts] Trimble Resolution-T SMT caught behaving badly

Michael Tharp gxti at partiallystapled.com
Tue May 15 03:21:16 UTC 2012


On 05/14/2012 09:11 PM, Mark Sims wrote:
>
> Attached is a Lady Heather screen dump of a Trimble Resolution-SMT timing receiver behaving badly.  The first quarter of the plot the unit was tracking all sats above 0 degrees/0 dBc.  The next quarter the masks were set to 30 degrees/30 dBc.   Then at the half way point,  something strange happened...
>
> The green plot is the sawtooth correction value.  It should be +/- 15 nS,  but was only running +10/-13 ns.  At the half way point the sawtooth started spiking down to -38.000000 ns...  obviously some internal clipping limit.   It ran this way for a day,  then I reset the unit and all has been well since.
>
> The purple plot is the unit's "local clock bias".  It is reported like the Tbolt's PPS value.    It is a sawtooth that covers a 1000 usec (almost) range. It repeats over a 28 minute period.
>
> The white plot is the "clock bias rate".  In comes in like the Tbolt OSC value.  Yellow is temperature.   Note how well those two plots track each other.   Suggests that some active temperature control might be useful.
>
> One nice thing about the Resolution receiver is that it returns tracking info for all sats,  even those below the elevation/signal masks.  This lets you build a signal level map even when you have elevation and signal level masks set.   Also note the high signal levels.  On a Tbolt,  I never see signals past green... the receiver is 6 db more sensitive.

Thanks for your notes on this device. I just got mine in the mail today, 
along with a 40dB antenna. Unfortunately I don't yet have the cable to 
connect the two, so right now it's running from a short length of bare 
wire, indoors, and as such can't really get a decent fix :-) It has 
managed to lock onto 4 satellites though, so it seems to work well 
enough to give me something to look at until I get materials to make a 
cable.

I am planning on making a simple NTP server using the Resolution SMT as 
the PPS input and a Rb oscillator (or any other 10MHz clock) to clock 
the CPU on the computer. If people are interested in a friendly 
interface board to the device let me know. My initial interface board 
design puts the PPS on the Carrier Detect line at RS-232 levels as is 
typical for this sort of thing, but USB is also very easy to do.

Regarding the default protocol being TEP, I easily managed to 
reconfigure it for TSIP using GPS Studio. The current version (1.08.0) 
supports TEP, and using Tools -> Configurator you can reprogram the 
Resolution SMT to use TSIP or NMEA by default. There are several other 
parameters that can be reprogrammed per the manual, including the width 
of the PPS.

Cheers,
-- m. tharp



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