I have a brand new MB 1200 sonar, but I cant seem to get it to work. What happens when I flick the Alt Hold switch at low altitude, (~2m) is that my quad will rise slowly and then at about 10m then the motors slow down and the quad just drops. I have attached a log file from that flight as suggested by Randy and it seems that the baro and sonar readings don't tally. Do I have a bad sonar? II have already installed the resistor/capacitor filter and use a 2 core shielded cable to connect everything up. And yes, I did choose the correct sonar in APM Planner.