Ozbusdriver,
You are on the right track, a C145 chip is for incorporation as a component in a system board, say an IRS/FMCS or an EGPWS system board, but nothing to do with VFR v. IFR. As an slight oversimplification re. RAIM, fundamentally all C129/129A/C145/C146 GPS produce position and rate information suitable for IFR navigation.
Seems to me the only equipment standards for VFR navigation relate to a compass and a clock.
For example, the GPS engine in the EGPWS of the new RFDS PC-12 provides the information to the ADS-B function of the transponder, as I am informed.
C146 is for a GPS engine integrated on a circuit board that includes additional components, processors, memory and programming that provide for, say, a moving map or other navigation , with ARINC serial outputs for additional functions, such as an instrument display/autopilots.
In fact, both the C145 and C146 TSOs have a matrix of sub-standards, labeled from Alpha to Gamma, which defines futher capability, and suitability for specific functions. Thus, a unit from Freeflight Inc., quoted in an earlier post, is C-14X Alpha, and as such, is not a suitable position/rate source for WAAS/Precision vertical navigation - sadly not likely to be an issue in Australia, unless the forthcoming Aviation White Paper comes up with something right out of left field..
By contrast, the GPS being quoted by Garmin to feed its 1090ES ADS-B transponder is the GPS output from their UAT box in isolation, and is C-146 Gamma, WAAS enabled, with all the bells and whistles.
If you go the Garmin way, the irony is that you will be carrying around the full Garmin FAA UAT box, but without any access to the available broadband functions, and in all likelihood, the AA ground receiver you are broadcasting to will be the Thales box also being supplied to FAA, but with the UAT (and possibly, VDL-2 voice/4 ADS-B) processor card slot(s) on the mother board left empty.
Your further investigation will reveal that, once 1090ES or UAT ( or VDL-2/4 ??) aircraft signals are received at the ground station and processed, the output to ATC computers are agnostic to the inbound information source format.
Maybe the FAA aren't so dumb, after all, in having a dual system, it almost guarantees no swamping from limitations imposed by number of available transponder codes, 4096.
Tootle pip!!