I have Put a Mikrotik RouterBoard and switched on but the signal strenght i too low... I can only get signal on 400m radius. Its put on B system .. Is there anything else that I can do cause I`m sure that this is not a good configurated.?

Maybe you have the wrong antenna connector on the radiocard selected ?
If not try another pigtail , some new ones don't work so well.
If its quiet radiowise around you don't need much power to cover good distance ( with a good antenna on 2.4 , radiocard set to 1db will go > 30 kms )