The whole goal of the LF inductively coupled RFID systems is very short
range. 10" is a stretch for these systems in normal applications. If you
want more range, make the coils physically larger while keeping to the
specifications for the silicon properly addressed.
Dave = W?LEV
Dave - W?LEV
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On Wed, Jun 15, 2022 at 4:39 PM Chuck, KF0CT <chu_r@...> wrote:
But why would anyone want an RFID reader that can read cards over 10" away
except to read someone's Credit card or Debit card without the person
knowing about it... then you just watch them type in their pin number and
you have complete access to their credit/debit card....
________________________________
From: [email protected] <[email protected]> on behalf of
tjackson382000 <tedj1@...>
Sent: Tuesday, June 14, 2022 8:20 PM
To: [email protected] <[email protected]>
Subject: [nanovna-users] NanoVNA for RFID design
I'm sure that at least a few here are familiar with the following section
from the STMicro application note "AN4974: Antenna matching for
ST25R3911B/ST25R391x devices", since it calls for the use of a VNA and the
ST25R391x is an RFID reader chip, supporting several standards. What I'm
confused about is line 4. And I'm not sure of the nanoVNA setting for line
5 (Q factor measurement). Can anyone brief me on what the author is saying
there exactly? I'm by now familiar with the open/short/50ohm calibration
procedure of course, but intermediate level in re-exploring the many curvy
zen mysteries of... the dreaded Smith Chart and applying the procedures
within AN4974.
Also, does anyone here have actual experience with the design of reader
impedance matching and tag antenna design for those chips? In other words,
has anyone ever survived AN4974 and lived to tell about it? Finally, I
need to design an RFID system (I chose the ISO-15693 standard for its
relatively long range, although I would LOVE to hear about any other
standard for which cheap front end chip solutions exist). Requires a 3"
diameter tag antenna and any diameter below 5.5" for the reader antenna and
a read range of up to 10" and must merely read out its unique UID code when
detected. Am I dreaming? Sound feasible? Many thanks to anyone who might
be willing to offer a little experience and advice, and I'd discuss
compensation if an expert is willing.
7.3 Verification of the Q factor in the frequency domain
The Q factor can be measured using a vector network analyzer and an
ISO10373-6 Class 1-3 calibration coil. The following steps should be
carried out:
1. The network analyzer shall be calibrated for a frequency sweep from
about 10 to 20 MHz
2. S11 measurement in log mag format shall be displayed.
3. The calibration coil is connected to the VNA.
4. ¡°Short¡± calibration of the coil and conversion to ¡°Z: Reflection¡±
5. Set marker 1 and enable the bandwidth/Q factor measurement
6. Place the PCD antenna on the measurement coil Note: If the reader is
plugged and powered, ensure that register 0x27 is set to 0xFF to avoid an
high power transfer to the VNA ports, which can damage the VNA.
7. Adjust the suitable trim value via the register map (register 0x21) in
the GUI of the reader
8. Place a 3 ? resistor between the RFO pin to simulate the chip
resistance during operation.
9. Press ¡°max search¡± to align the marker on the resonance frequency peak
of the PCD antenna Figure 33 shows the results of such a measurement.
#applications #coils #design #matching #nanovna
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
Dave - W?LEV
