ads link budget

anyone has a tutorial on Link budget simulation in ADS. Such as how to use the function bug_gain(), etc. I have tried the examples and read the mannual. When i change the components into my system. Everything is invalid. I have no clue how to fix it. I have tried only a simple sysyem i.e. a mixer and an amplifier. I used AC simulation. It work ok. but when i change to HB simulation to get the bugget of IF, it does not work.