RFID Diagnostic card not indicating on desktop reader

I bought a $10 125khz USB “desktop” reader off amazon. It’s about the same size as a proxcard and has an actual wire coil inside that takes up about 3/4 of the unit… It reads cards at 3" distance. The XLED lights up when perpendicular to the coil but only when very close.

The RFID diagnostic tool doesn’t light at all. I put it every which way around the coil, even through the hole in the center of the coil and nothing.

The card does work on my S7 NFC and the ID-12A from sparkfun in the punchclock.

Am I correct in thinking it’s just due to the differences in the antenna designs?

In other news, the ID-12A was able to read the xEM inside the injector which surprised me a bit. The desktop reader didn’t, which did not surprise me. lol

Interesting… not sure why the RFID Diag card is not reading it… it might be a coupling issue or the card may be damaged. Can you check any other 125khz readers with it?

As for reading the xEM in the needle… yes at 125khz this is totally possible because the skin effect of AC is much less at the lower 125khz frequency than it is at 13.56mhz, and a lot of the field penetrates the metal of the needle just fine. This is why so many “rfid blocking” products don’t actually work all that well for 125khz cards and tags, only 13.56mhz cards like credit cards… but there a mathematical probability that given the correct reader antenna and power output could even overcome those blocking wallets and read the cards inside. The needle is much thicker than the blocking material in wallets, so even thought it’s mathematically possible to read an HF tag inside the needle, it is not practically possible.

The card works fine with the ID-12A (125khz) reader. -shrug-

Odd. It’s hard to get a 125khz antenna printed on PCB… that’s why they are usually wire wound whereas 13.56mhz antennas are easily printed. it’s possible that the shear size of the printed antenna on the RDC is physically too large to be efficiently and completely enveloped by the field generated by the reader’s antenna… so there may not be enough power produced in the RDC to light the LED.

Can you send me a link to this reader? I’d like to get one and test this theory.


Oh yes… I’ve seen these… and yes they have a coupling issue with the RDC. The power output and antenna design both conspire to create a low Q factor and while that’s good for tags, it’s not enough to power the LED on the RDC.