GPS Zero Baseline Test

James Suttles

Active Member
I am looking at project, that requires the following:

Global Positioning System (GPS) equipment shall undergo a zero baseline test. A zero baseline test is a test on two or more receivers simultaneously gathering data from one antenna. The data shall be post-processed to give a resulting vector between the receivers that is equal to zero.

I spoke with Adam, and he had mentioned that Matt has been working on this or something similar. Can our Equipment meet this requirement. If so, what Antenna and resulting cable should I look at pricing into the proposal? This test will have to be done every month for the entire duration of the project, which will be around 21 months> A log of this test and the Total Station calibrations will be kept and submitted upon request. The total station hast to be calibrated once a month on an approved, by the owner, EDM Baseline and an Approved third party vendor has to be included in the adjustment of the Total Station, to check all level vials, horizontal and vertical circles, etc.

So you can see the specs are gonna be tight, and I need to know how best to perform the Zero Test Baseline with our equipment.

Thx
 

Adam

Well-Known Member
5PLS
@Matt Johnson have you done any comparisons of two LS's on same firmware like James will need to do? I told him I think it should give the same results as long as the recievers are identical and the firmwares are the same.

What splitter should doug get? Which antenna did you use?
 

Adam

Well-Known Member
5PLS
Doug doesn't have the external antenna connections. The external connecter hardware is on the LS, is this an OAF update only or would he have to send them in? He does have two LS's. I see the price for the external connection is $500 each.
 

James Suttles

Active Member
So basically a capital expenditure of $3900 or so, if all the options are picked, minus the external power supply. Plus $500 each on the External Connections on the LS's?

Real quick question. Is the DC listed on the slitter for Direct Current that is provided from one of the LS's and the other LS will not be supplying any power to the antenna?
 

Matt Johnson

Well-Known Member
5PLS
Doug doesn't have the external antenna connections. The external connecter hardware is on the LS, is this an OAF update only or would he have to send them in?

If the units have the ports then it should just require the OAF option.

Is the DC listed on the splitter for Direct Current that is provided from one of the LS's and the other LS will not be supplying any power to the antenna?

Correct
 

Steve Douty

Well-Known Member
Can anyone direct me to a paper/articel that explains the process of, theory and usefullness of a zero baseline test? I must admit that this is the first time I have heard of it!
 

Matt Johnson

Well-Known Member
5PLS

Adam

Well-Known Member
5PLS
Yes



A zero baseline test is used to observe any internal interference and noise that might be created by the receiver. See Introduction to GPS: The Global Positioning System
Matt, if you haven't done so yet will you run the test to see if they are in fact equal? Javad has even said no receiver is equal This maybe chasing a rabbit down a hole. Too many times I've seen hunndreth specs on projects that don't need it. I've actually had some change the specs to what I say I can do. Is it possible to hit zero on this test?
 

Adam

Well-Known Member
5PLS
There is likely some tolerance for "zero", Adam. I doubt it is perfectly "zero". Probably 0 +/- some few mm.
As I recall, Doug said zero per the contract he may be signing. Forgive me if I heard him wrong, he qouted several specs. Maybe he will chime in. I asked him if they were paying with bags full of gold.
 

James Suttles

Active Member
Here is the section that talks about the testing of equipment.

H. Tolerances for all other work shall be as shown or specified in the Project Documents.
I. Survey instruments shall be accurate and subject to inspection by Owner for proper operation.
1. Check and calibrate electronic distance measuring instruments used on Site a minimum of
once per month on an established base line approved by Owner. Keep calibration results in a
log book, available for review, showing the date and distances measured on the same base
line. Do not use an electronic distance measuring instrument if it does not meet the
minimum advertised accuracy published by the manufacturer.
2. Global Positioning System (GPS) equipment shall undergo a zero baseline test. A zero
baseline test is a test on two or more receivers simultaneously gathering data from one
antenna. The data shall be post-processed to give a resulting vector between the receivers
that is equal to zero.
3. Promptly replace, repair, or adjust defective survey instruments to operate within the
tolerances of the instrument manufacturer.
J. Remove and replace all Work not performed with the methods and equipment as submitted and
approved.
 

Sean Joyce

Well-Known Member
Now I am curious about whether anyone has had GPS equipment get out of tolerance and fail this test and then what is done to the equipment to bring it back into tolerance.
You have to love the guys that write these absolute specs.
 

Aaron S

Active Member
Sorry for butting in on a topic that's probably over my head, but if both receivers are using the same antenna, and processing the same signals with the exact same software/firmware, why wouldn't the difference be zero? Wouldn't the math be the exact same between them if the LS's could "show their work"?
 

Sean Joyce

Well-Known Member
Sorry for butting in on a topic that's probably over my head, but if both receivers are using the same antenna, and processing the same signals with the exact same software/firmware, why wouldn't the difference be zero? Wouldn't the math be the exact same between them if the LS's could "show their work"?


From Matt Johnson's post above- all receivers are not created equal.
A zero baseline test is used to observe any internal interference and noise that might be created by the receiver. See Introduction to GPS: The Global Positioning System
 
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