On Thursday, May 3, 2018 at 7:32:41 PM UTC-5, Dirk_PW wrote:
I like where WB is going with his original question. And why not, fundamentally it shouldn't be that hard...

1) Have all ADS-B, Mode-C, Mode-S, and Non-xpdr radar targets get stored in a common database.
2) Through an app on a cell phone, have it downlink your current position, velocity, altitude, etc to the same database.
3) Through the same app, have it upload all targets from this same database that is within your vicinity and graphically display them.

The only hardware needed here is a cell phone. The only connection you need is a cell tower. The hard part is getting access to all the ATC surveillance data in one database. And the main limitation on the user would be connectivity to a cell tower (which I have found to be quite reliable in the air). If you look at this from a "basic situational awareness point of view" (sans collision avoidance), it would be very powerful and everyone would use it.

I just flew my Phoenix Motorglider from Charlotte to MN. At lower altitudes, you can get pretty good cell phone connections. However, as you get to 6,000 ft or higher, the cell phone coverage becomes very dicy. At 8,000 ft I had virtually no coverage during the entire trip.

A number of years ago I was in New York. On the observation deck of the Empire State Building, I had no cell phone coverage.

I have T-Mobile as a provider. Maybe other carriers work better at higher altitudes. However, I think relying on cell phone coverage for any kind of collision avoidance is a highly questionable approach.