[time-nuts] Trimble UCCM survey results

Bob Camp kb8tq at n1k.org
Tue Dec 20 14:54:10 EST 2016


The simple answer is that you want to do the survey on the specific GPSDO you will be using. 
You feed the results of that survey back into the GPSDO as it’s fixed location. There are a number
of subtle issues that can creep into the GPS module’s location estimate. Whatever the issues are,
they are also (hopefully) built into the survey data the GPS reports. This is also another reason to
run very long surveys (many days). That way you include as much of the weirdness into the survey
as you can.

Would it be better to have a perfect GPS that is always correct in all regards? Sure it would be. Since
these devices are done on a budget that is probably not going to happen. A GPS module that originally 
sold for < $50 is not going to compete with a $4,000 survey receiver (which also may have anomalies). 


> On Dec 20, 2016, at 1:28 AM, Tom Curlee <tcurlee at sbcglobal.net> wrote:
> A couple of questions:
> I've just started using  LH 5.0 with my 2  GPSDO units (Thanks Mark!) - a Trimble UCCM and a Z3801A.  Oddly, I'm very getting different survey altitude values.  The Z3801A is around 81 M, which agrees within 1 or 2 meters with Google maps (not a perfect source, but close), but the UCCM is usually around 48M to 53M depending on which survey I want to believe.  Both receivers are locked and both are fed off the same antenna through a splitter.  I admit that the antenna placement is very poor - anything below 60 degrees elevation to the north is blocked (LH is great for antenna placement analysis).  Anyone have any ideas?
> A question on LH usage.  When the UCCM is in the position hold mode, what happens when a precision survey is run?  Looking at the .lla file shows that every position, including the final processed location,  is the same as that shown as the position hold location on the main LH screen.  Do you need to take the receiver out of the hold mode to run a precision survey?  How?  How is the position scatter plot used with a survey?  I usually don't see any positions plotted, certainly not when running a precision survey.  I think I saw data plotted when I did an internal survey.
> Many thanks for any info.  And thanks again to Mark and John for all the work.
> Tom
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