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Re: |S11| > 1
Chuck,
Take a read of Bob Witte¡¯s measurement equipment books, written when he was at HP. Joe Carr¡¯s tests and measurements book is another one rendering a cogent treatment of measurement errors without going very deep into the statistical deep-end. This work is based upon formal true-score theory: the central issue of which is whether the observed score¡¯s errors are correlated with the true score and/or the observed score. 73, Frank K4FMH |
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Re: NanoVNA for RFID design
If you need 10"+ reliably, use the 950 MHz or 2.45 GHz system at lower
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power, not these inductively coupled systems. Dave - W?LEV On Wed, Jun 15, 2022 at 5:04 PM Tim Dawson <tadawson@...> wrote:
Things like automated package/baggage sorting use RFID at times, and-- *Dave - W?LEV* *Just Let Darwin Work* --
Dave - W?LEV |
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Re: NanoVNA for RFID design
The whole goal of the LF inductively coupled RFID systems is very short
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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 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-- *Dave - W?LEV* *Just Let Darwin Work* --
Dave - W?LEV |
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Re: NanoVNA for RFID design
Yep! That's in an MF ISM band. If one has a Metcal soldering implement,
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it also operated in this band. Those having a TinySA, this offers an easy "target" for checking MF operation. Dave - W?LEV On Wed, Jun 15, 2022 at 1:26 PM W1RS <Deflatermaus@...> wrote:
Nice story on the history! I agree that the coupling for the RFID is-- *Dave - W?LEV* *Just Let Darwin Work* --
Dave - W?LEV |
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Re: NanoVNA for RFID design
Thank you
________________________________ From: [email protected] <[email protected]> on behalf of Jim Lux <jim@...> Sent: Wednesday, June 15, 2022 6:45 PM To: [email protected] <[email protected]> Subject: Re: [nanovna-users] NanoVNA for RFID design On 6/15/22 9:39 AM, Chuck, KF0CT 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.... A good use case is where you use the badge to authenticate into a computer (using an actual contact badge reader that uses the cryptographic chip in the badge), but then just need to make sure that the user is in the vicinity. If you require the badge to be resident in the computer, it makes it hard to use multiple computers at the same time. A typical PIV-II credential has both an RFID (which returns only the serial number of the badge) and an actual chip (like in a credit card). ISO14443A/B ISO ISO15693 are two of the specs ISO/IEC 15693 systems operate at the 13.56 MHzfrequency <>, and offer maximum read distance of 1¨C1.5 meters They do both ASK and FSK. As far as NanoVNAs go, it's a useful tool to develop and test these kind of systems - 13.56 MHz is easily choked with ferrites to remove the cables and instrument from interacting with the system. So you can set up a test card (which has the antenna, but a SMA or MMCX connector on it) and a test reader (just the antenna, with connector). And this is at a frequency for which the NanoVNA is perfect. You can easily set up a scripted environment, have a user wearing the badge on a neck lanyard and move around while logging S21. |
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Re: NanoVNA for RFID design
On 6/15/22 10:04 AM, Tim Dawson wrote:
Things like automated package/baggage sorting use RFID at times, and distances to objects on a moving belt canrequire this kind of reach. Exactly - there are document management systems that put RFID stickers on each page or folder of the paper document (think mortgages and similar docs).? Then they have a reader that goes in front of a box of several hundred/thousand docs and inventories the box.? Imagine in your mind a 20 foot high shelving unit with a robotic device that places and retrieves boxes. |
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Re: NanoVNA for RFID design
On 6/15/22 9:39 AM, Chuck, KF0CT 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.... A good use case is where you use the badge to authenticate into a computer (using an actual contact badge reader that uses the cryptographic chip in the badge), but then just need to make sure that the user is in the vicinity.? If you require the badge to be resident in the computer, it makes it hard to use multiple computers at the same time. A typical PIV-II credential has both an RFID (which returns only the serial number of the badge) and an actual chip (like in a credit card). ISO14443A/B ISO ISO15693 are two of the specs ISO/IEC 15693 systems operate at the 13.56?MHzfrequency <>, and offer maximum read distance of 1¨C1.5 meters They do both ASK and FSK. As far as NanoVNAs go, it's a useful tool to develop and test these kind of systems - 13.56 MHz is easily choked with ferrites to remove the cables and instrument from interacting with the system.? So you can set up a test card (which has the antenna, but a SMA or MMCX connector on it) and a test reader (just the antenna, with connector).? And this is at a frequency for which the NanoVNA is perfect.? You can easily set up a scripted environment, have a user wearing the badge on a neck lanyard and move around while logging S21. |
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Re: NanoVNA for RFID design
TY
________________________________ From: [email protected] <[email protected]> on behalf of Tim Dawson <tadawson@...> Sent: Wednesday, June 15, 2022 5:04 PM To: [email protected] <[email protected]> Subject: Re: [nanovna-users] NanoVNA for RFID design Things like automated package/baggage sorting use RFID at times, and distances to objects on a moving belt canrequire this kind of reach. - Tim On June 15, 2022 11:39:33 AM CDT, "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....-- Sent from my Android device with K-9 Mail. Please excuse my brevity. |
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Re: NanoVNA for RFID design
RFID expert here. I had a quick look at the AN. It is quite complex to grasp in 60 seconds. I did some 13.56 MHz antenna design before, but these were all for a 50 Ohm system impedance, so you can have a few meter of coax cable between reader and antenna.
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Your primary goal is to measure the inductance of the loop antenna and the add resonating capacitors. Adding a parallel resistor may be needed to lower the bandwidth, otherwise the tag's modulated backscatter signal will be attenuated. There is a trade-off. A high Q allows for a high antenna current which gives you a large activation range. However, the tag signal will be attenuated. If the reader is really sensitive, that may be fine. You can also tune the antenna to one of the two sidebands. This will give an increased range since transmitter power is still fine and the reception of either lower or upper sideband is also fine. Some reader chips try to decode both sidebands and select the strongest. As a rule of thumb, range is approximately equal to reader antenna size. A large tag antenna size and optimized antenna tuning may give you some extra range, but I doubt you'll be able to reach 10". I tested two different reader chips and they had quite different performance. I just forgot which parts, but I'm pretty sure the STM chip was one of them. I'm on holiday now, no access to my notes from many years ago. To chear you up, it was not that difficult as it looked. But you'll have to have a firm grip on VNA measurement techniques to know what you are measuring. A VNA alway gives an answer, but it could be very wrong... Luckily, at 13.56 MHz, a few cm of wire does not shift the phase too much and it allows for some tolerance. The margins at 915 MHz are much smaller. Another rule of thumb that may help in initial loop design is that every mm is approximately 1 nH of inductance. Calculate one turn and multiply by the number of turns squared. Good luck! Reinier Op 14-6-2022 om 22:20 schreef tjackson382000: 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. |
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Re: NanoVNA for RFID design
Things like automated package/baggage sorting use RFID at times, and distances to objects on a moving belt canrequire this kind of reach.
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- Tim On June 15, 2022 11:39:33 AM CDT, "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.... --
Sent from my Android device with K-9 Mail. Please excuse my brevity. |
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Re: NanoVNA for RFID design
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 |
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Re: NanoVNA for RFID design
True. Antenna is a misnomer, and the tag and reader coils act together as a 'loosely coupled transformer', I think is a proper term. And yes, the ISO 15693 standard includes a 13.56 MHz carrier. The tag is energized by the field produced by the modulated primary coil, and the tag responds by modulating (intermittently shorting) its own secondary coil (amplitude shift keying), which is detected via induction by the primary coil and its associated front-end electronics. Thanks for all the background. Fascinating technology. But... any answer to my actual questions, please? Lol.
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Re: 2port measurement determining Zdut with S11 and S21
Hello all of you,
Op za 11 jun. 2022 om 22:11 schreef Victor Reijs < pe1atn.victor.reijs@...>: Thanks for all the feedback provided. If I gain more experience, I willHere is my web page on my experiences. I think S21 and Y21 methods look promising using my NanoVNA-H: All the best, Victor |
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Re: |S11| > 1
Thanks to DAve W0LEV and others for bring up the subject of error analysis and significant figures.
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My own background is like Dave¡¯s; a physics degree in 1965. Our professor in senior labs was very big on error analysis. It¡¯s a hard subject. I asked at our local hospital regarding uncertainty and error in lab tests. I never got a good answer. A friend of mine, an engineering professor, made a joke ¡. ¡°If you want to be absolutely certain about a measurement, only measure once.¡± Do I need to explain? Chuck KF8TI On Jun 14, 2022, at 1:49 PM, Jim Lux <jim@...> wrote: |
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Re: |S11| > 1
I do not have a VNA. I rely on Rudy Severns, N6LF, for data. He recalibrated his VNA at the SMA connector, measured a short there, and now MA mode does not affect the file data. In addition, |S11| is no longer greater than 1.
Sorry for the confusion. I would delete my original post if I could. Brian |
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Re: NanoVNA for RFID design
I am one of several engineers who worked for the company that originally
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introduced RFID to the world, AMTEK. They no longer exist as many start-ups go. The company was fresh off "The Hill", Los Alamos, where RFID was originally developed to log and to some extent, track, Pu and other radioactive carrying trucks. Dr. Gary Seawright purchased the patent rights from Los Alamos and formed the company. Those systems operated in the 915 MHz and 2.45 GHz ISM bands with an experimental license from the FCC. When AMTEK was bought out by the Texans (that was the end of a good beginning!!), Gary resigned. Another engineer, Dr. Jerry Landt, also left shortly after. Jerry wrote and still participates in authoring most of the RFID standards we have today for the RFID industry. The rest is history........ So much for history. I was there. However your system is a low-frequency inductively coupled system that likely operates below 150 kHz. Even though the coupling element is referred to as an "antenna" is it not. You are dealing with inductive coupling between the tag or badge and the reader coils. I did not work on these systems, but am quite familiar with them from much later work before I retired. I note the required equipment lists only a Network Analyzer. There is a big difference between a Scalar and Vector network analyzer, both in performance and cost. The NANOVNAs are vector analyzers, but can be used as a scalar analyzer as well. A scalar analyzer can not produce Smith Charts as it does not measure the angle of the measurements and, therefore, can not represent complex impedances or deal with Smith charts. That is accomplished with a VECTOR network analyzer which is far more complex and dwells with the Smith Chart. So,........., if there is no need for measuring complex portions of the impedances of the antennas (inductors) (which I do not read in AN4974) you're off the hook for a lot of complex arithmetic and the Smith Chart! Dave - W?LEV On Tue, Jun 14, 2022 at 8:20 PM tjackson382000 <tedj1@...> wrote:
I'm sure that at least a few here are familiar with the following section-- *Dave - W?LEV* *Just Let Darwin Work* --
Dave - W?LEV |
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Re: |S11| > 1
Brian,
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As a reference point, when calibrated, the HP 8753D has a linear magnitude reflection uncertainty of 0.015 or so when the reflection magnitude is near 1. I am not sure if that means the repeatability is limited to that or if that is due to imperfections of the standards used. (Source: Quick Reference Guide, 08753-90259, page 7-5) --John Gord On Tue, Jun 14, 2022 at 02:45 PM, Brian Beezley wrote:
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Frank K4FMH
tjackson382000
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