GPS DROTEK XL Problems! Precision exceeds 10m

Hello community,

I tested the DROTEK GPS RTK XL on the ground, and I have a precision between 5m and 13m on the ground.
1- I would like to know how I can improve this accuracy?
2- Is there a way to integrate an antenna with the GPS? If yes, how?
3- For flight tests, the GPS does not contain an SD card. I bought a datalogger. However, I do not know how to implement it in my system, and connect it to GPS XL. Do you have any ideas for this?

Thank you in advance.

Can you please help?
Thanks you for answering my questions.