historically, aircraft have those antennas mounted on their belly and with low power they blast them at the ground for powerful receivers to catch. For "ADS-B D

historically, aircraft have those antennas mounted on their belly and with low power they blast them at the ground for powerful receivers to catch. For "ADS-B Diversity", which is the space based version, on a generic Cessna 172 that meets current ADS-B requirements, I would need to rip out my current ADS-B system and replace it with a $9,000 (plus labor) ADS-B system that has dual broadcasting antennas. I think the top mount antenna is also more powerful but I honestly do not know. Space based ADSB only improves coverage for mountain ranges and oceans. It's mission in a mountainous situation is to fill the gap when radar coverage is lost but you have low altitude (in relation to ground, not sea level) traffic, such as arriving and departing traffic. assuming this map is accurate, you can appreciate how aircraft below 15,000 ft would be constantly falling in and out of ADS-B coverage if they themselves were changing altitude.