SJ
SIL = Source Integrity Level and at level 1 it is the lowest level of quality from a certified GNSS source. Most military aircraft have certified GNSS receivers in my experience. Oh, and many military aircraft have GNSS systems that can be more accurate than civilian systems if the selective availability is turned back on. A certified GNSS receiver isn’t that expensive and the £419 hand portable ADS B In/Out Skyecho 2 has one and so therefore can emit ADS-B at SIL=1.
Most ATC units or ACAS systems will ignore anything that is SIL=0.
i hope that helps?
LJ