Transponder Question


I was tracking a Qatar Airways flight. Virtual Radar Server was showing mode S transponder, but it changed a few minutes later to ADS-B. Is this normal? I thought they were two different systems, albeit on the same frequency.


ADS-B is mostly done in the Mode S Extended Squitter (ES), so if your receiver has only seen a few Mode S frames but not enough for a full ADS-B message, it may identify it as Mode S.


Aha…thanks. First time I saw/noticed this.