[time-nuts] Trimble SMT 360

Michael Wouters michaeljwouters at gmail.com
Tue Apr 19 19:21:03 EDT 2016


Dear Bob

( I shouldn't write email while walking around doing the housework!)

The possibility of other constellations causing a problem was one of the
things I checked, running it in GPS only mode. No improvement.

Cheers
Michael

On Wednesday, 20 April 2016, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> Actually there is one other possibility:
>
> If you have more than one “system” enabled *and* it’s doing “all in view”
> *and* it’s applying that
> to the timing *and* the population in view changes significantly … (whew !)
>
> As the solution pops between GPS and Glonass, you will get a time shift.
> Since it’s a “which one
> is right?” sort of thing … Trimble probably does not want to get into the
> debate. They would love
> to sell stuff to everybody.
>
> Bob
>
>
> > On Apr 19, 2016, at 3:32 PM, Logan Cummings <logan.cummings at gmail.com
> <javascript:;>> wrote:
> >
> > Hi Michael, Bob,
> >
> >     I had been very curious about this myself - the new ICM SMT 360
> > modules at first glance seem like a great deal - < $50 and 10MHz TCXO
> > disciplining built right in.
> >
> >     I came across this paper which compares the older (GPS-only) ICM SMT
> > to a LEA-6T - the Trimble fares poorly in their testing.  The graphs
> don't
> > show an issue quite like yours Michael, so I'd be curious about the line
> of
> > questioning Bob brings up, how many satellites are being used by the
> > receiver - say in GPS-only mode?
> >
> > http://www.imeko.org/publications/tc10-2013/IMEKO-TC10-2013-028.pdf
> >
> >    Does anyone else have comparative experience with the new SMT modules
> > from Trimble? RES or ICM?
> >
> > Thanks,
> > -Logan
> >
> > On Tue, Apr 19, 2016 at 4:01 AM, Bob Camp <kb8tq at n1k.org <javascript:;>>
> wrote:
> >
> >> Hi
> >>
> >> The two plots shown appear to be identical. If they are actually two
> >> different
> >> runs, the problem repeats very closely.
> >>
> >> If the GPS is not in position hold *and* the antenna is less than ideal
> -
> >> That’s
> >> the sort of thing you may see. Essentially it’s got two locations it
> >> “thinks” are
> >> correct. Another possibility is a position hold situation with a very
> low
> >> satellite count.
> >> As a single observed satellite goes in and out of multi path, the
> solution
> >> goes all over the place.
> >> Again, you need a challenged antenna for this to happen. Pretty much all
> >> of this
> >> would be apparent from the normal messages out of the part.
> >>
> >> Bob
> >>
> >>
> >>
> >>> On Apr 18, 2016, at 10:13 PM, Michael Wouters <
> michaeljwouters at gmail.com <javascript:;>>
> >> wrote:
> >>>
> >>> Does anyone have  experience with the Trimble SMT 360 ?
> >>>
> >>> I bought some of these four or five months after they were released.
> >> During
> >>> testing, the 1 pps output evidenced a problem, as shown in the attached
> >>> plot (the 1 pps is being measured against a Cs  beam standard), which
> is
> >>> not sawtooth-corrected. While there are longish periods of nominal
> >>> operation, the receiver seems to hop between two solutions.  This
> >> behaviour
> >>> is well out of specification.
> >>>
> >>> When I contacted Trimble support, they said that the firmware in the
> >>> receivers was very early, and replaced the receivers. However, the
> >> problem
> >>> was still evident with the new firmware. Trimble did not respond to
> >> further
> >>> emails.
> >>>
> >>> I tried many things to isolate the problem, including restricting the
> >>> receiver to GPS-only but I was unable to make an improvement.
> >>>
> >>> I would like to know if anyone else is operating an SMT 360 and if they
> >>> have seen any similar behaviour.
> >>>
> >>> Cheers[image: Inline image 2]
> >>> Michael[image: Inline image 1]
> >>> <smt360.png><smt360.png>_______________________________________________
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