Has anyone tried to do this?

I have two GPS receivers, and when they are near each other, they calculate different positions. The difference is about 5-10 meters, but in reality it is several centimeters.

So, I'm trying to do this, connect two receivers to one antenna. And again I get different positions. The difference is about 1-2 meters. The receivers are the same model and on the same boards. The other receivers work well.

So, has anyone dealt with something similar?

As I think, if they are connected to the same antenna, the calculated position should be the same.

May be somebody has two GPS receivers that are the same and can test this...?

  • $\begingroup$ Can you add info about the antenna cables? Their length and material might effect the solution a bit. Did you use two different antennas for the first trial(5-10 meters difference). Did you or can you interchange the receivers (to eliminate/observe cable issues). $\endgroup$ May 25 '17 at 11:39
  • $\begingroup$ I haven't looked into in in awhile, but aren't consumer GPS systems generally only accurate to within a few metres? Wikipedia suggests an accuracy of 5 m. You shouldn't expect to get the exact same readings. $\endgroup$
    – JMac
    May 25 '17 at 11:49
  • $\begingroup$ The accuracy you can get depends on the receiver, especially the decoding software. The best possible accuracy that can be achieved is a few millimeters, but you get what you pay for, and there is a tradeoff between accuracy and the speed of decoding - for example in a vehicle satnav system, it might not be very useful to know "exactly" where you were 15 seconds ago! $\endgroup$
    – alephzero
    May 25 '17 at 13:36
  • $\begingroup$ Cables RG 223 3 meters length. Receivers Ublox neo 7p with declared accuracy less than 1 m. If one signal comes to two equal receivers, it must be treated equally and the same location is obtained, isn't it? $\endgroup$ May 25 '17 at 14:20
  • $\begingroup$ Can you reverse the cabling (connect cable A to receiver B, and cable B receiver A) and try that too? If the values do not change, he problem is the receivers, if the values change, it's the cables. In theory, your readings should be quite close (within the 1m accuracy of the receivers, so at most 2 meters apart). Make sure that the antenna is receiving enough satellite signals. $\endgroup$ May 26 '17 at 9:19

Even when connected to the same antenna, two identical receivers might come up with different navigation solutions. Their analog front ends have different sensitivity and noise figures as a result of normal manufacturing tolerances. Their internal clocks are not synchronized, and among other things, these effects might cause them to choose different subsets of the visible satellites for their solutions.

Precision applications (e.g., GPS interferometry) need to take this into account. They typically work with the raw pseudorange and range-rate data associated with each satellite, making sure to select a common subset of satellites from both receivers. There is also usually a provision to have them running on a common internal clock.


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