When we use the word “performance” in relation to transponders, we are referring to an intricate dance between many factors to make the overall experience of placing the transponder up to a reader as easy as possible.
This dance involves many partners including antenna performance for both transponder and reader, power requirements of the transponder, power transfer efficiency between the antennas, inductance, impedance, capacitance, resonance, the physics of magnetic field shapes, and a little bit of black magic thrown in for good measure.
The ultimate Gen 4 magic chips consume a bit more power then standard Gen 1 or Gen 2 chips do. The small antenna size of the flex series makes achieving the required power transfer a bit more difficult.
I have noticed though that the Proxmark3 Easy HF antenna is just not great at picking up most flex designs. I think this has to do with that magnetic field shape issue, more than raw power output or anything like that. There are also some oddities in the antenna design which twist the magnetic field up a bit in some key places;
Typically only one via is needed to cross over the spiral loop coil on a PCB to bring both ends of the coil to the oscillator, but for whatever reason they make the coil traces here do looptyloops not once but twice… it’s like forming a twist-knot pastry with the magnetic field, and this will fuck shit up with small antennas trying to magnetically couple with that mess. Larger transponder antennas will do ok with it because they have plenty of inductor spread across a larger area… and smaller x-series can avoid the mess by straddling just one small straight section of the coil path… but flex antennas are right in the shit zone.
The best place I have found for flex on the PM3 Easy is basically right over the serial number on the sticker on the back. Not the barcode, the serial number itself.
