I need to learn a lot, where to start? - Page 1
Forum section: electronics / rf-microwave

author: jpyeron
author_rank: Regular Contributor
timestamp: February 17, 2025, 02:19:02 pm
content: I am a digital (VLSI) guy, this was what I went to school for. Recently, you saw my failure of RF knowledge. Some back story.At work we have a project which involves a PN532 NFC RF design component. We interviewed RF consultants, hired 2, one delivered, worked in the lab, failed in the field.While I am nowhere near qualified to do the work, I was chosen to supervise the work, since I was the most qualified EE. I am again going to have to supervise the next RF engineer consultant.I thought I had the task under control. I reviewed the documentation, which included design write up, assembly write up, and testing write up.The project may have had a fundamental requirements failure. Or, it may have had a design failure. I do not know enough to identify which.My learned gaps are:* I do not know the how or why of antenna characterization and testing* I do not know the how or why of validating transmission / reception** Measuring / validating power efficiency* Characterizing interference and shielding* there are things I don't known that I don't know.As an example, the engineer proposed 2 changes, which I both approved, knowing I did not understand the theory or math behind it. I had him explain it, and they made logical sense.1. was a change from modifying the PCB (with a differential antenna trace) to add a connector to coupling a second antenna2. was changing the coupled antenna from a single ended design to a differential design.Heck, I am struggling to even figure out where to start learning about the difference between single and differential antennas.So, given I am not the best at calculus and similar math, been out of school for 30 years, where should I start learning? What should I scope the learning too so I can hire and supervise RF engineers?

author: rf-fil
author_rank: Regular Contributor
timestamp: February 18, 2025, 05:20:36 am
content: It takes a few semesters at uni, plus some years of experience to be reasonably good at RF design. An easier way to manage this kind of project is to make the RF engineer responsible for the outcome - i.e. don't micro-manage them. Just make sure the end goal is agreed and understood. And, importantly, who carries the risk. Specifically, development of this type can take often longer than expected. Make sure it is agreed and understood who is paying for it.Btw, I've not done much NFC but I've seen in get super difficult whenever you try to do something slightly non-standard or different from the evaluation boards. Like, a different form factor, or different coil shape, etc. Or having the coil in proximity to large metallic objects. Or having the reader and the tag unusually far away from each other.

author: Poroit
author_rank: Frequent Contributor
timestamp: February 18, 2025, 06:53:47 am
content: G'day jpyeron,As @rf-fil stated, "years of experience"...not just study but also hands on inhouse and out in the field.Don't knock yourself out trying to know it all.It looks like the 2 changes suggested were both to improve the RF range/connectivity so read up on antenna power/gain etc so you have enough knowledge to keep the engineers honest.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 18, 2025, 08:03:56 am
content: NFC antennas are completely different from any other antenna design. For example, with NFC you are using near field, while with traditional antennas, the goal is to get a good far field radiation pattern. With NFC you do not want any far field radiation (good way to fail EMC). One of the ideas of NFC is also that unused power gets recycled, so you aren't using a lot of power by having the NFC antenna transmit. In the same way that an ideal inductor doesn't lose power, ideally the NFC coil doesn't lose power too. Because of all of these reasons, you're not going to learn much by looking at classical antenna designs.NFC antennas are closer to transformers than actual antennas, since they are not designed to actually radiate any signal beyond a certain point. The coil on the PCB forms the primary, and the card has the secondary (all NFC cards have another coil on them). The NFC chip on the card receives power from the PCB coil (the mechanism is like a transformer), and then the NFC chip on the card shorts out the coil on the card. This steals power from the PCB coil and allows the chip on the PCB to detect a 1 or a 0.To do NFC antennas right, you first need to find the following data:- The source impedance of the chip (potentially something like 50 ohms but maybe not)- The size and number of turns you want (NXP should have an antenna calculator somewhere). Having a larger loop is helpful if you want NFC to work further, but it might not be possible.- Matching components (the antenna is matched by adding a capacitor, so the inductance of the PCB coil resonates with the capacitor and results in a mostly resistive impedance). A NanoVNA should be able to do this measurement. You want to get the impedance shown by the NanoVNA as close as possible to the source impedance of the chip as listed in the datasheet. There are plenty of articles about how to use the NanoVNA to check your NFC antennas. Of course use a real VNA if you have one.- Bandwidth (What data rate are you doing?) The Q of the LC circuit is very important since it limits your bandwidth. If your Q is 20 then you can't do any of the higher modulation rates. Most of the time you need to add a resistor to lower the Q of the PCB antenna + capacitor. (In every other RF antenna adding resistors is bad because it will destroy your output power, but NFC antennas are different). If you want to go above 102 kbps, you will need a Q of around 8 if I recall correctly. This information should also be in the datasheet- Metal objects near the antenna. Metal objects will cause you to lose power because of eddy effects (think of a metal sheet as a transformer with 1 turn that is shorted). One classic mistake is putting a ground plane under the PCB coil. You will need ferrite shielding if you have metal nearby.In any case just follow the datasheet's recommended design/layout if you're unsure. A lot of it is probably also software, but you're good at that. Try messing around with the transmit power and receiver sensitivity. Make sure to read all of the application notes too for your specific chip, since they will tell you how to do all the math related to NFC. You can easily compare NFC transmit power by making a coil of wire and hooking it up to an oscilloscope.

author: jpyeron
author_rank: Regular Contributor
timestamp: February 18, 2025, 01:52:12 pm
content: Everything so far has been very helpful, thank you.Quote from: rf-fil on February 18, 2025, 05:20:36 amQuote from: Poroit on February 18, 2025, 06:53:47 amThese are the goals.Quote from: rf-fil on February 18, 2025, 05:20:36 amYep, that's the balancing act. Keep costs in check vs finding an engineer willing to take the project and be able to deliver.Quote from: EggertEnjoyer123 on February 18, 2025, 08:03:56 amThese are perfect examples of why I am trying to learn enough to lead the project, not do it. I understand that I am not the RF engineer.That being said, some books that found in my searches:Design Constraints for NFC Devices by Dominique ParetAntenna Designs for NFC Devices (Waves) by Dominique ParetNear-Field Antenna Measurements (Artech House Antenna Library)Near-Field Antenna Measurements (Artech House Antenna Library) by Dan SlaterThoughts on the book list? Again, my goal is to communicate with the engineer so the task gets done right and everyone is happy.

author: LM21
author_rank: Regular Contributor
timestamp: February 18, 2025, 09:24:59 pm
content: This is may be a silly question, but do you need to know it all, isn't it your experts/subcontractors job to know. Is there any steps where you can verify that something is done, and progress is achieved.

author: Kean
author_rank: Unknown
timestamp: February 18, 2025, 09:39:04 pm
content: Quote from: jpyeron on February 18, 2025, 01:52:12 pmThose NFC specific books sounds good as NFC is HF RFID, and much like LF RFID it operates in near field rather than far field as mentioned by EggertEnjoyer123.Maybe grab some more fundamental RF books?RF Circuit Design by Bowick is highly rated, maybe something from ARRL, or look for other RF starter books on Amazon that don't cost a ridiculous amount.I still need to get back to studying this stuff.

author: jpyeron
author_rank: Regular Contributor
timestamp: February 19, 2025, 12:15:49 am
content: Quote from: LM21 on February 18, 2025, 09:24:59 pmIn a perfect world, I absolutely wouldn't need to know anything. Not silly, it was what I thought last time. This time I will know a little bit more.Quote from: LM21 on February 18, 2025, 09:24:59 pmThat's where I failed last time, and resulted in me brining 2 bags or water in to the datacenter as an emergency fix.Quote from: Kean on February 18, 2025, 09:39:04 pmIt is on the shelf at work, going to reread the first few chapters to understand more on Q.Quote from: Kean on February 18, 2025, 09:39:04 pmIt is a work project, Money is of no importance. I want the stones.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 19, 2025, 03:34:39 am
content: My advice is to read every application note for your chip first. Also look at the evaluation kit (generally the design files are provided for free). The app notes are generally written well enough that the lay engineer can understand.There also should be simulation tools provided by NXP. See here:https://www.nxp.com/company/about-nxp/smarter-world-blog/BL-NFC-ANTENNA-DESIGN-MADE-EASYOf course, always make sure that there is no metal close to your antenna (or any magnetic materials like ferrite)

author: KE5FX
author_rank: Super Contributor
timestamp: February 19, 2025, 04:02:54 am
content: Get accounts that give you access to the current frontier models on Google and OpenAI, and possibly (political leanings permitting) xAI.No, really. Do that. Disregard the chorus of barking nitwits who will pop up any minute now to discourage this course of action.Bowick's good, too, but o1-pro with Deep Research is a superpower. Learn to play these models off against each other, and you will be able to obtain actionable, explainable, and verifiable answers on almost any topic you throw at them.

author: Poroit
author_rank: Frequent Contributor
timestamp: February 19, 2025, 06:44:53 am
content: Att. EggertEnjoyer123,Thank you for your insight into NFC antenna.What is your opinion of the two mods the RF Engineer proposed to the OP?

author: jpyeron
author_rank: Regular Contributor
timestamp: February 19, 2025, 12:29:18 pm
content: Quote from: EggertEnjoyer123 on February 19, 2025, 03:34:39 amOur issues stem from the "innovative" changes to move the antenna a few meters from the chip. Per the primary design requirement.Quote from: EggertEnjoyer123 on February 19, 2025, 03:34:39 amYeah, working on that too. There is more metal, switching power supplies, etc. around the installation location than a scrap yard. Hence - worked on the bench, but not in the field.Quote from: KE5FX on February 19, 2025, 04:02:54 amWTF? I am assuming this is sarcasm, but I don't get it.Quote from: jpyeron on February 19, 2025, 12:15:49 am@Kean, Thanks - read first 3 chapters last night, one more tonight. Flash backs to college. Probably going to need to read them twice and find a lab exercise to make it stick.

author: Kean
author_rank: Unknown
timestamp: February 19, 2025, 01:31:52 pm
content: Quote from: jpyeron on February 19, 2025, 12:29:18 pmI am trying to locate my copy, but no luck yet *. I had to relocate a bookcase a while back when there was a pipe leaking in my office ceiling. Only a few books were damaged thankfully.FYI, I recall that the web link in the book for the "companion site" athttp://books.elsevier.com/companions/9780750685184That no longer works, but I found they are now athttps://booksite.elsevier.com/9780750685184/?ISBN=9780750685184* I may happen to have a PDF copy as a backup...

author: KE5FX
author_rank: Super Contributor
timestamp: February 19, 2025, 05:43:35 pm
content: Quote from: jpyeron on February 19, 2025, 12:29:18 pmxAI's newest Grok model is competitive with o1-pro according to Karpathy and others. That means that (like it or not) it's potentially very useful.You can file me under 'not', for what it's worth. I don't have an X account, so I don't have access to it myself. But it needs to be mentioned for completeness' sake, I think.

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2025, 08:01:20 pm
content: Quote from: KE5FX on February 19, 2025, 04:02:54 amExcept where they are not.Consider this article, from somebody that works in a field where they will try almost anything - for good reason. He is more than open to significant improvements, and keeps looking for them - but he insists on "kicking the tyres" of each and every new technology. Hence he indicates where Deep Research did well.It is abenefitthat 99.99% of us won't understand the detailed domain terminology in his article - because that allows us to focus on the general points that will be valid in all domains.https://www.science.org/content/blog-post/evaluation-deep-research-performance"...the query I chose was 'I want you to write a research report on summarize the toxic effects of thalidomide with respect to different species and different isomers of the compound, and what’s known about the mechanism for those effects <tggzzz omitted>' I chose that for several reasons. First off, it's a reasonably technical topic, and I wanted to see how the Deep Research system dealt with the chemistry and toxicology literature in general. Second, it's one with several complications, and there are many misconceptions that have proven difficult to get rid of. ... It's definitely a topic with some heft to it."

author: KE5FX
author_rank: Super Contributor
timestamp: February 19, 2025, 08:35:38 pm
content: Quote from: tggzzz on February 19, 2025, 08:01:20 pmThis just in: guy from industry with a replication crisis of existential proportions criticizes LLMs for emphasizing older works rather than newer ones.

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2025, 08:50:35 pm
content: Quote from: KE5FX on February 19, 2025, 08:35:38 pmThat is a cherry-picking summary.Why did you pick those cherries rather than the others he mentions?I chose not to quote part of his article in order to avoid such problems.I suggest anybody interested in understanding the characteristics of LLMs should read his entire article; it isn't long.

author: KE5FX
author_rank: Super Contributor
timestamp: February 19, 2025, 09:47:12 pm
content: I don't think his article makes the point you are thinking/hoping/wishing for. The only relevant question is, what happened when he gave it the same task 12 months ago, or 24?24 months ago: "This thing hallucinated a bunch of random crap. Total bollocks."12 months ago: "It got some stuff right, but still missed major points and made several glaring errors."Today: "It asked clarifying questions, cited its sources, and didn't hallucinate anything at all. But for some reason, it overlooked this one detail that I think would have been well worth including. Also, for reasons I'm personally certain of but can't articulate to save my life, it's not really 'reasoning.'"

author: tggzzz
author_rank: Super Contributor
timestamp: February 19, 2025, 10:12:44 pm
content: Quote from: KE5FX on February 19, 2025, 09:47:12 pmEr, no.I'm not interested in history, I'm interested in characteristics - especially those that trip up "the man on the Clapham omnibus" and youngsters.I note that youngsters are triumphantly rediscovering "active research topics" that were first encountered 40 years ago, and then forgotten.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 20, 2025, 07:12:14 am
content: Quote from: Poroit on February 19, 2025, 06:44:53 amI'd have to see pictures to understand what is going onQuoteWhy is this necessary? The chip is small and the antenna itself will probably take up more space. You could probably put the chip inside the loop even and still get better performance. It is way easier to route digital signals over a few meters than it is to route an RF signal.QuoteBuy a ferrite backing for the NFC antenna. Like this:https://www.mouser.com/datasheet/2/223/MCP-DS-MHLL%20SHEET%200814-606086.pdfAll the magnetic fields will go through the ferrite instead of making it to the metal.

author: jpyeron
author_rank: Regular Contributor
timestamp: February 20, 2025, 02:56:29 pm
content: Quote from: EggertEnjoyer123 on February 20, 2025, 07:12:14 amWhat pictures? I will see what I can oblige.Quote from: EggertEnjoyer123 on February 20, 2025, 07:12:14 amThese are the requirements, and I cannot go in to the why we have those requirements - secret squirrel stuff.Quote from: EggertEnjoyer123 on February 20, 2025, 07:12:14 amCool, bought some samples. 100% to 150%, 2 each. Will do some A/B testing with them.Mfr.:Laird Performance MaterialsDesc.:EMI Gaskets, Sheets, Absorbers & Shielding Flex Ferrite Sheet 13. ...Mfr. #:MHLL5040-000Mouser #:875-MHLL5040-000Mfr. #:MULL6060-300Mouser #:875-MULL6060-300Mfr. #:MSLL6060-300Mouser #:875-MSLL6060-300Quote from: KE5FX on February 19, 2025, 05:43:35 pmOk, will add to the mix. I will treat them like interns and see what they bring to me.Quote from: jpyeron on February 19, 2025, 12:29:18 pmHad a nightmare last night about Is, Js, Pis, Ls, Ts, and Qs. Somehow omega was absent from the dream.

author: rf-fil
author_rank: Regular Contributor
timestamp: February 21, 2025, 10:32:27 am
content: Few other thoughts... when I said "sometimes things take longer than expected".. I mean it. In this type of R&D, where there is some new aspect to the solution, it may take 10x longer, 100x longer. Or it may not be reasonably feasible at all. I'm not trying to be facetious. This actually happens quite often. Are you in this situation right now? Are you sure that what you're trying to do is feasible?I have seen this a fair bit. Projects get conceived and commited to, before the technical feasibility is established. The most devious ones are a type of a technical tarpit where things seem reasonable, especially if it's outside of one's expertise: "Let's make the room allowed for the antenna slightly smaller." "Let's use a 500mAh battery instead of 800mAh.", "Let's take 20% off the target BoM cost." A "small change" like this, and the project is dead (and you might not know it). Btw, this is hard to fix late in the project. The risk of this issue ocurring can be minimised with good systems engineering practice in early stages. Anyway, I'll get off my high horse, lol.As others have said, NFC coils are near field antennas - it's in the name. They work a bit differently than other "antennas". They are more like transformers. Issues with NFC coils are related to their tuning and coupling. This can be debugged with EM solver software. Not cheap either. Or, empirically with building prototypes and testing in-situ with VNAs and other test equipment. If you suspect a tuning issue, you can replace the key tuning capacitors with variable ones and manually adjust the system until it works. Then measure their values and replace them with fixed values.

author: rf-fil
author_rank: Regular Contributor
timestamp: February 21, 2025, 10:43:10 am
content: Quote from: jpyeron on February 19, 2025, 12:29:18 pmSo you have some sort of transmission line between the chip and the "antenna"? Has that been properly factored into the design? Is there a model in LTSpice or ADS or whatever that proves that this can even work? I don't understand that requirement anyway... why not keep the chip near the coil and just run a comms/power cable to it? This is just bad architecture.

author: LM21
author_rank: Regular Contributor
timestamp: February 21, 2025, 03:41:07 pm
content: What about evaluation kits. Many products have such. They wont probably solve your R&D projects, but they could help. And they make learning phase easier.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 22, 2025, 07:52:52 am
content: Just going to put this out there but if you're not careful with how you connect the PCB to the antenna you will have an EMC nightmare too.The best way is probably using two pieces of coaxial cable to connect the two ends of the antenna to the PCB. Put 2 SMA connectors on the PCB for the positive and negative transmitted signal from the chip. Then put two SMAs on the antenna side, one for each side of the antenna. The ground of the SMAs connects to the center of the antenna and the ground of the PCB. You will have to determine how the cable affects impedance matching though, and it will be a lot harder than just putting the chip with the antenna.

author: rf-fil
author_rank: Regular Contributor
timestamp: February 23, 2025, 06:38:57 am
content: Quote from: EggertEnjoyer123 on February 22, 2025, 07:52:52 amThat would only work if both antenna connections are ~50 ohms. If it is just a coil, the impedance at each terminal will be inductive and nowhere near 50 ohms. So, putting a coax in there would adding the capacitance and inductance into the circuit. Coax impedance is sqrt(L/C), isn't it?If OP wanted to use a cable, they would need to factor the inductance and capacitance into the circuit. I am not sure this can even work...

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 23, 2025, 06:45:28 am
content: Quote from: rf-fil on February 23, 2025, 06:38:57 amPut the matching network on the antenna side. Surely you can fit a few 0201 components, right?

author: jpyeron
author_rank: Regular Contributor
timestamp: February 24, 2025, 11:01:26 pm
content: Quote from: EggertEnjoyer123 on February 22, 2025, 07:52:52 amThis is more along the v1 approach, prior to the RF engineer consultant took over.Quote from: rf-fil on February 21, 2025, 10:32:27 amNot a high horse - been there done that.No, I am not sure what was proposed, poorly tested, and approved is feasible. I think this is why the subject is "I need to learn a lot, where to start"Quote from: rf-fil on February 21, 2025, 10:32:27 amYep, that is giving me hope... EM solver software software recommendations? Limited to the ones provided by the NFC chip manufacturers so far.Quote from: rf-fil on February 21, 2025, 10:32:27 amBack to my job of creating test and evaluation criteria.Quote from: rf-fil on February 21, 2025, 10:43:10 amQuote from: rf-fil on February 23, 2025, 06:38:57 amQuote from: EggertEnjoyer123 on February 22, 2025, 07:52:52 amAgain, we willing to go back to the drawing board, but I don't know enough yet.Quote from: LM21 on February 21, 2025, 03:41:07 pmSo many of these... could fill a ball pit.