@Loco9 

If Deco app shows low signal for Satellite unit, you must move that unit closer to Main Deco. 

I am assuming you are talking about low signal from Show List screen in Deco app, such as:

  @Alexandre. 

Yes man that what I talked about , but the unit is not so far barley 10 meters from the main unit it is not supposed to be so low in so small length 

  @Loco9 

What is between the two nodes?   Im guessing you have walls and this isnt open space?   If so what are they made of

Distance is irrelevant when you include walls, doors, glass and metal which are all sources of interference, reflect or absorption.     The average stud wall will drop signal 3-5db which is roughly half to two thirds, a solid wall -9db which is around 80% loss

WiFi and walls dont mix sadly!