So the scoop on this is that yes ISO15693 is more “RF sensitive” than ISO14443A, meaning it requires less power to do its thing, but with reduced bandwidth. For the most part, this translates to a net % gain in what I call “RF performance” … which is a collection of features that includes “read range”. However, because this is a % based improvement based on energy transfer, the % gain can basically be mapped to antenna performance in general… meaning if you test two tags with identical antennas head to head - one is ISO14443A and one is ISO15693, then the ISO15693 tag is going to out perform the ISO14443A if tested with the same exact reader in the same exact position (tests are identical). But again, the gain is % based… so ISO7810 ID3 cards which already perform really well with most readers will see a lot of gain while tiny little transponders like the x-series, which don’t perform very well really, will see a negligible gain… and that’s what I’m seeing here with my Spark 1 vs my xNT.
That said, I think what is more important is another aspect of what I call “RF performance”… and that is coupling sensitivity. Put another way, how “exact” does the orientation of an x-series chip need to be to get a good read. My xNT can basically work with most readers at a 45 degree angle to the reader antenna coil, meaning I have about 90 degrees I can work with to get a good read of my xNT… but I also need to pretty much be right on the money with that antenna coil - it must be over the chip pretty much exactly. If there is an offset of even a few mm, then the read angle reduces by quite a bit. This is where the “RF sensitivity” of the Spark1 and xSLX work in a noticeably better way. I can see a registerable improvement in both offset tolerance and rotational angle, meaning I don’t have to be as exact when dropping my phone down on the Spark 1 as I do with my xNT. That’s a bankable improvement over simple “read range” by any standard.