I am starting to get questions!  Many are answered elsewhere but, I'll try to answer some here


Table of Contents

  1. How do I ...?
  2. Where can I find ... ?
  3. Why does (n't) ... ?
  4. Who is ... ?
  5. What is ... ?
  6. Can ... ?

How do I know if the computer is talking to the receiver?

Gpsrcvr does a short self test before it lists the channels and what is going on.  The test is not comprehensive.  A new program (gpstest) has been added to the bottom of the software page and in the CVS directory.  If it runs properly you can be sure that the computer to receiver interface is working.

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Where can I find the source code ?

The source code is provided in two places.  The most recent version will be available on this website.  In addition the most recent version is maintained under CVS at Sourceforge.  All of the versions from 1.09 to the most recent are available for downloading at the main osgps page at Sourceforge.

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Why doesn't it track any satellites ?

First, check that you are using an active antenna with at least 26 dB of amplification.  Second, be sure that you have a clear view of most of the sky and a tight cable connection.  If possible use another receiver to check out the antenna setup.  The most common problem is having the wrong time zone in the RCVR_PAR.DAT file.  A less common cause is having the computer time or date incorrectly set.  The satellites searched for are predicted based on the almanac, time, and location setting.  If any of these is too far off the wrong satellites will be searched for.

Why does it track more than 4 satellites but does not come up with a navigation solution?

The most likely problem is the computer time/date setting.  If it does not agree with the time received from the satellites to within 5 minutes it will not produce a navigation fix.

Why does the receiver only track a couple of satellites ?

Again, this is most likely due to the computer clock/date setting.  The satellites searched for are predicted based on the almanac, time, and location setting.  If any of these is too far off the wrong satellites will be searched for.

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Who is ... ?

[This is the answer to the question.]

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What is the accuracy it provides ?

The hardware uses a single frequency at L1 so the primary source of error is Ionospheric delay.  In test runs it has provided about 2.5 m CEP (50th percentile) in the horizontal plane and about 4.5 meters LEP (50th percentile) in the vertical direction.  Of course this was not compared to a surveyed location so there could be bias in the position fixes.

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Can the software be used for other chipsets ?

In general each chipset has it's own peculiarities and the software cannot be used without some degree of modification.  The downconversion scheme dictates how the carrier is tracked.  The software is customized for the GP2021 which has two correlators per channel with 1/2 chip spacing between them.

Can the software track WAAS/EGNOS satellites?

No.  This version is not set up to track the WAAS/EGNOS signals.  The GP2021 can be configured to track these PRN codes and all it would take is a software modification.

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Clifford Kelley
Copyright 2001  All rights reserved.
Revised: March 13, 2004 .