Hi Doug, having done quite a few RFID antennas, that 1 to 1 is rather optimistic.
One thing to consider, do you have any other metal within a foot or so of the antenna?? ?You can easily see a pair of pliers passing a foot or so from the loop.
Good luck with your project, Kent WA5VJB
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On Saturday, July 16, 2022, 11:00:36 AM CDT, Douglas Butler <sherpadoug@...> wrote:
I have a 125 kHz RFID antenna consisting of a coil and series tuning capacitor.? The manufacturer supplied plots of the SWR and Z of the antenna showing a nice 50 Ohm 1:1 SWR at resonance.? I have tried to replicate these plots using my newly purchased NanoVNA and I get radically different plots showing a load closer to 25 Ohms and a 2:1 SWR.? Measuring the L and C separately gives about the same readings I get with my HP4801 vector impedance meter at 125kHz, but it is near the upper frequency limit of the HP4801 so results are shaky.? I calibrated the NanoVNA over the same range as shown in the manufacturer's plots.? My Smith plots are centered on the horizontal axis like I would expect them to be.? The manufacturer's plots are shifted up to the inductive half of the Smith chart.? Both show a nice resonant dip at 125 kHz.
Am I doing something wrong?? Is the antenna manufacturer lying?
SherpaDoug WA1UWP
