It is possible that it is a counterfeit. I did my little investigation and I found clues for this possibility. I'll still test what @grampy said right after for more clues and I will give my results then. I tried what you said @clive1, and I had really poor signal for a really short time (minimum : 10 dBHz max : 28 dbHZ) according to the "statistic view" of u-center.
Therefore, I'm always in "No FIX".
Here are my clues for the counterfeit possibility. On this image you can see there is no FIS or EXT entry (on the right side is my text console; on the left is ublox' forum page. According to this, my Flash parts are missing (conterfeit theory).
I also have the counterfeit's drawbacks described by Ublox's services.
Do you think that, even it's a counterfeit, I can have better results with an SMA antenna instead of the integrated one ? My project is'nt that big, it's just for practice.