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Open Letter to Customers - Satellite Issues May Cause GPS Problems |
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October 23, 2009 Dear Customers:
We have seen lots of problems with GPS the last few days from 1:30 to 3:30 in the afternoon. There have been as few as 4 satellites available during that time. I am thinking that tomorrow may be similar, as well because of an odd cycle with the orbit of the satellites.
Normally, this low number of satellites in view happens during the night and early morning. We have not typically had this problem. I have a few things that we can do to help you keep running. However I want you to realize that these changes could allow you to run, but the accuracy is not going to be there during these periods of only seeing 4 or 5 satellites. I am trying to find out why we are having these issues and how long they should last.
I have included a typical chart of satellites in view on the 6-10-2009.
 visibility-6.10.09.pdf
Also there are two charts from this week with SBAS turned on.
visibility-10.20.09.pdf visilbility-10.21.09.pdf
First a FMX, 500 or a 250 can use SBAS or the WAAS satellites in the position fix. This will allow us to pick up 1 to 2 extra satellites at all times. Go to setup then GPS and then to GPS Limits. Make sure that “Use SBAS in position fix” is turned on. Then you can raise the PDOP up to 8 or even 10. Completing this will allow you to keep running, although you will not be as accurate when the PDOP is high. Take the “Minimum number of satellites from 5 to 4. This as well could cause inaccuracies but will let you run when you only have 4 satellites.
Another thing that you could do, but do this cautiously, is lower the elevation mask from 8 to 5. The problem with this is in good GPS times it could cause you to be inaccurate due to having a poor quality signal coming in from a low satellite. Then go in and hit edit WAAS. We want 135 turned on and all others turned off. As a last resort we can turn on 138 as well, it will give you an extra satellite but you could see position jumps when you switch from one satellite to the other.
262 Receivers make all of the changes that we want done to the 500 but it will have to be done through a laptop, FMD or Pro 600.
252 and the old EZ Guide do all the same settings as the 500 accept the SBAS settings since these receivers can’t use SBAS in the position fix but again you have to have a laptop, FMD or Pro 600.
EZ Guide Plus does all of the same as the 500 except the SBAS settings since these receivers can’t use SBAS in the position fix. But, this can be programmed through the EZ Guide Plus.
The other option is to leave the receiver alone and just not steer during those times.
GNNS receivers are not affected by these issues.
If you want more information or have questions to post, go to our Facebook page by searching for Allied Environmental Group.
Doug Wical
Field Technology Lead
Allied Environmental Group
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