The periodic pattern in double difference of pseudorange (NEO 8T)

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I want to check the noise level of pseudorange of UBLOX receivers (NEO 8T). I put two receivers at the same location with a clear sky. From my knowledge, the double difference should be like noise. However, when I calculated the double difference of Pseudorange, I found there were periodic patterns in them. The maximum is about 10 meters, and the period is around 50 secs. Can you please tell me why this happened?

This is not caused by the reference satellite. If I changed the reference satellite, the problem remained.Note that the pseudorange is obtained from RAWX messages.

by wengweng asked Apr 28, 2016
by wengweng edited Apr 28, 2016
0 votes
Have you reviewed the local clock performance in the individual receivers? Have you looked at the clock reset bit signalling that the clock is being slewed due to the accumulation of bias? Look also at NAV-CLOCK, pay attention to the drift, and the bias, which I'd expect will slew once +/-1ms of bias has accumulated, and then look at that with respect to your periodicity, and how they differ with respect to each other. Although 50s seems a bit frequent.

When looking at the two sets of pseudo-range make sure you are doing the comparison at the same instant in time. And if you need to correct the measurement based on the local time in the receiver.
by clive1 answered Apr 28, 2016
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