For those that are thinking about buying the generally more expensive 1090es devices instead of the cheaper 978 devices, in case you might want to fly into Canada’s controlled airspace in the future, make sure you get a top mounted antenna (as well as a bottom antenna for the USA) From AVWeb: Most U.S. general aviation operators will Not be able to fly in Canadian controlled airspace and vice versa when Canada mandates ADS-B according to Nav Canada. The not-for-profit corporation is also majority owner of Aireon, a recently activated space-based ADS-B tracking system that requires ADS-B 1090ES transmitters with antennae on the Top of the aircraft to properly track them. The U.S. uses a ground-based system that requires belly-mounted antennae. Aireon has tested belly-mounted antenna with its system and they don’t work. Nav Canada is telling Canadian pilots that its system will be exclusively based on the satellite system and they should be making their equipage decisions accordingly. In most cases, it’s not as simple as adding a second antenna to be able to fly in controlled airspace in both countries. Only a few GA systems offer the so-called “antenna diversity” ability.