Originally Posted by jeffsvan
My first install (before all the ADS-B equipment) was a GTN650 with GTX330 transponder. This could show a terminal area traffic on the display.
I believe that traffic is called TIS-A ?
Later I had the GTX330 transponder upgraded to a GTX330-ES.
This satisfied my ADS-B Out requirement.
I added a portable GDL39 antenna so I could see ADS-B IN on my I-pad.
I am assuming that equipment sees the new TIS-B traffic.
My avionics shop said I could keep the TIS-A active on my GTN650.
It would do no harm. Eventually TIS-A would be obsolete.
Everything was working fine for many months, however, the last few weeks I am getting continuous false alerts on the GTN650 (TIS-A) showing a target 0 miles and 100 ft lower in altitude. I believe this is my own aircraft.
Nothing shows up on the I-pad and I see no other traffic near me.
I assume now I will need to shut off the TIS-A on my GTN650?
I searched the GTN650 menus and could not figure out where/how to do that.
My airport is located under a class B .
You can disable TIS-A traffic in the GTX 330ES setup. Doing this should make the problem go away, but of course you lose all traffic on your GTN since it doesn't sound like it is connected to an ADS-B receiver. You may eventually need to also disable the RS-232 traffic interface between the GTX 330ES and the GTN.
Some of the newer 1090ES transponders like the GTX 345/345R/45R and GNX 375 don't even receive TIS-A traffic anymore.
Do you have more than one pressure altitude source supplying your GTX 330ES and/or GTN 650? It sounds like the ownship traffic identification is failing since it is seeing a traffic target 100 ft below the aircraft.
If this only happens when you are climbing or maneuvering, it could just be the normal delays which are present in TIS-A traffic. By the time your aircraft receives an update of "you" on the ground uplink, there is sufficient altitude and/or position split that the system treats it as another aircraft and alarms.
Your GDL 39 does not receive TIS-A traffic, so that is why this has not been an issue except on the GTN.