Hi Ian,
After I received the document I phoned the chap up in Germany and quizzed him on the minimum version as it conflicted with advice others had been given that had been shared with me.
Ours appears to be too old to upgrade - funny as it basically seems to work !!
If, by "basically seems to work", you mean it outputs SIL=0 and SDA=0 then that may well be true.
However..... I was advised by NATS that a couple of transponders in their uncertified GPS ADS-B trial output faulty GPS position coordinates (flipped minus sign on LAT or LONG). And the Funke chap on Friday said that there were bugs in the pre-v5.3 code to do with intermittent faulty GPS position. I put 2 and 2 together!!!
As I now understand it, Funke started providing support for ADS-B from v4.8 onwards but 100% correct support for uncertified GPS ADS-B is only from v5.3 or later.
Steve