I talked today to Filser and Becker, and they both confirmed that their
mode-S transponders will support extended quitter with GPS information
transmitted, if a GPS is connected in the near future. It will be a
software update.

Marc Ramsey schrieb:
Why would you want a Mode S transponder to be fed by a GPS? The
Extended Squitter variation of ADS-B does layer on top of the Mode S
downlink protocol, but simply feeding GPS data to a Mode S transponder
will not make it ADS-B compliant. An entirely new box will be needed.