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GPS signals over time

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please see this picture:

http://www.webx.dk/rc/video-wireless/gps-t...lerup-14hrs.gif 14hr

http://www.webx.dk/rc/video-wireless/gps-t...lerup-20hrs.gif 20hr

http://www.webx.dk/rc/video-wireless/gps-t...lerup-24hrs.gif 24hr

http://www.webx.dk/rc/video-wireless/gps-t...lerup-35hrs.gif 35hr


I have recorded the sats trace over 14 hrs, my home location is Denmark City Ballerup,

we can clearly see there is a black hole right north of me.

each sat have a revolution time of 12hrs, but the earth spin at 24hrs

so the ground trace is not a circle going arround the globe, but looks more like a sinus with flat top.

the program I used to make this picture is called VisualGPS and is freely downloadable from:


if any of you could please record a similar screenshoot ?

say also over 14hrs and see if your location is gps friendly or not,

I will be happy to see the results.

Edited by ThomasScherrer

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ok it IS in fact the "black-hole" over the north pole I see !!

no GPS satellites pass directly over it,

it is exactly the same issue with the south pole.

I used http://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.html

to show the ground trace of all GPS sats.

so bad news to people in the north of norway or greenland,

I will expect them to have a bit more trouple with GPS signals on overcasted days

Edited by ThomasScherrer

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here is one more trace, made by Claus from Germany:

http://www.webx.dk/rc/video-wireless/gps-t...lueck-24hrs.gif 24hr


The north pole black hole is also clearly visible here.

claus told me he used http://www.visualgps.net/VisualGPSXP/default.htm

the program I used did not work with vista after sirfdemo has been runned, really wierd problem,

but the XP version of their Visual GPS program works a bit better, how ever it is a 30 day trial.

Edited by ThomasScherrer

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If you watch the track of the Space Shuttle or ISS, you will see the same thing. With a "flattened" map of the earth, it does look like a sinusoidal path. It is however, just a regular orbit that is "tilted" relative to the equator. The earth rotating underneath causes the slip such that the orbit eventually goes over the majority of the earth's surface, except for high and low lattitudes.

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exactly, but why did they not made a few of the GPS sats pass directly over the poles ?

maybe it is not possible ?

but ok how many people live on north norway, north greenland ? or on the south pole ?

those people MUST have a much lower sat count and also longer aqure time,

and if bad weater I expect them not to be able to get a sat fix.

I called a friend that worked along time on greenland, he said they do actually use GPS to navigate,

but if bad weater they stay indoor anyway :-)

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here you see 12 sats with EM406A in my window 1st floor :-)

note PRN124


here you see only 10 sats with EM406A in my window 1st floor :-)

note PRN120


here you see 12 sats with EM406A, notes:

PRN126 elevation 25, PRN 2 elevation 12

the geostationary GPS sats have hi PRN numbers, their location and names are here:


they can also be tracked with J track.

ok I have added a pre amp (LNA) and larger antenna to this EM406A to make it receive as much as possible.

actually I see it often push out sats to pull in new ones, the EM406A can only receiver 12 sats at one time,

I think I shuld try this antenna and preamp with a 20 sats receiver, just to see how many I can receive at the same time.

I start to get sats info allready at elevation 1-2 ! so I am quite happy about this modification

any use for this ??

no not at all, I do this just for fun and to learn more about this topic.

Edited by ThomasScherrer

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anybody know why I loose all info about the geostationary sats if I am not in SIRF mode using SirfDemo,

it looks like all normal NMEA programs I have dont suport it, or maybe they are not send out in non sirf mode ??

please help ?

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