Madhan bro is right,But I will add to it,when ever you add a another stb to LOOP-OUT then take care that the second box will only works on the Satellite which is working with first (Main) Stb.
I mean suppose you have 10990 V 27500 freq. of DD+ is active in your first stb then you are able to watch DD+ in second STB also, You can't access the other satellite apart from the active satellite.
In some stb's this is also seen: suppose the main stb is using Vertical polarization the second can't work on Horizontal pol. So few things we have to kept in mind. ok