Ok, and If I change the antenna of node 1 ( 2db ) by antenna of 8 or 12 db ?
Yes for the node 31, but if I change the antenna of node 1 ( See my Schema ).
Yes Node 1 is the nRF24L01 + PA +LNA like this ( http://img.dxcdn.com/productimages/sku_222913_1.jpg ) with antenna 2db
And the Node 31 has the nRF24l01 "classic"
Because with external antenna at the distant location, I have the same result.