Eliminating radio interference from Apple charger(oh8hub.substack.com) |
Eliminating radio interference from Apple charger(oh8hub.substack.com) |
How did this thing get FCC approval? What's it's FCC approval number? Who tested this thing? Want to look that up.
If RF got outside the charger and into the USB cable, it's very badly designed. The power in the USB cable is DC. There shouldn't be any significant RF component. There should be ferrite beads and capacitors in the power supply to deal with this. When the filtering is close to the switcher, it's much easier to deal with the noise, and very small ferrite beads, available in surface mount, can usually do the job. Once it gets out on an external wire, it's hard to filter.
This is an old problem for Apple. A report from 2013, from a pilot charging an Ipad in an aircraft.[1]
[1] https://pointsforpilots.blogspot.com/2013/06/radio-interfere...
Looking at the radio display, it seems like the peak power is about 7-8 S-units. At VHF, that would be about -100dBm; or about 100 femto-watts. I presume that the charger is pretty near the radio. With free-space path loss being inverse square law, it's essentially going to be completely negligible within a very short distance.
Oh, and if the antenna is indeed near the charger (say within one wavelength, 2 meters in this case) it might be inside the near-field - which means that you're getting additional power transferred that wouldn't be reaching the far-field, and you might even be affecting the behavior of the device due to coupling.
Looking at the FCC report, the radiated emissions are totally in-line with FCC Class B requirements.
Modern ham radio equipment has exquisitely sensitive receivers and you easily hear all kinds of interference from digital devices that are completely Part 15 compliant. The prevalence of switched mode power supplies literally everywhere has made HF radio completely unusable for many people outside rural areas.
On the other hand, aviation voice radios aren't very sensitive and navigation radios have filtering built-in. So the output of an Apple charger is probably some orders of magnitude too small to cause any issues.
Is this something a regular radio would detect, or is OP just trying to listen to a handheld radio half a continent away using a really sensitive receiver with the volume knob turned all the way up?
(I have not read the entire report and I have no expertise in RF.)
http://www.righto.com/2016/03/counterfeit-macbook-charger-te...
Very bad. Strange also because Apple usually gets their PSUs made by Delta afaik and they are as good as it gets.
Folks need to relax. People actually experienced with RF wouldn’t worry about this at all, and the FCC is perfectly capable of doing its certification job.
Well that isn't even remotely correct.
Any time you have switching, which this does, in DC you have VERY high frequency components in every rise and fall time. Much faster than your period or switching frequency, it's all about how fast you rise/fall. You switch, rapidly, through anything that has inductance, and you have RF.
Here's the schematic for a switcher I designed.[1] This is a strange application - USB power in, 120V out, to drive an antique Teletype machine. Without any filtering, there would be huge spikes in the DC across C1-C2. But it didn't take much filtering to fix that. There's a small ferrite bead at L2, and an RC filter at the snubber at R1-C7. The back to back Zeners are to absorb inductive kickback from the output electromagnet. That's the output side. On the input side, there's more noise suppression, to prevent injecting noise back into the USB power source, which is usually a laptop here. Note L1 and C12. Those are all tiny surface mount parts, total cost in quantity maybe US$0.20.
It's an exercise in LTSpice to get the values right and make the DC power smooth DC, in both voltage and current. This is well understood.
There are radio hams using this thing, and they report it's not blithering in the RF spectrum.
[1] https://github.com/John-Nagle/ttyloopdriver/blob/master/boar...
i didn't read the article and i don't know the expertise of the author, but depending on the type of antenna you use, you may have to choke literally every wire in the "shack", KB/mouse, power, speakers, ethernet, etc. Although, funny enough, this is for the inverse case - the radio messing with the computer!
I wonder if an RF choke (AKA a 1:1 Current Balun) directly attached to the UHF port on the back of the radio would help in this circumstance - the feedline is probably coupling with the USB cable!
Far better to use a linear power supply, which has a transformer and as a result is far heavier.
Wouldn't this then be a problem with whatever car charger he is using and not with the apple device plugged into that charger?
Fascinating. No wonders we have so much red tape on stuff that is in the air.
Maybe his magsafe charger really is bad, but if it's plugged into a computer or a crap charger it's also likely that it's just RFI riding the cable straight out of the computer. USB stuff is the worst offender in my shack -- the majority of USB cables are just a complete joke.
When I'd transmit on 20m, it would sometimes open my old liftmaster garage door. Until I wrapped all of its cables in ferrites.
Are we sure it’s a real MagSafe puck? The article didn’t check that.
Sadly copies of Apple stuff are so rampant, especially on Amazon, if you didn’t buy it yourself from a reputable retailer. It’s quite possible it’s a fake. The little white charger bricks were copied rampantly. With Apple’s prices the fakers stand to make a lot.
Given Apple’s normal engineering quality that would be my first guess. Or Bloggie’s guess it’s the PSU that’s the issue.
It’s interesting they found the problem, and that a simple ferrite bead fixed it.
But I have no doubt there are fakes out there for something g like the MagSafe puck. Without ruling that out simply declaring it a “piece of crap” seems unwarranted.
This isn’t true at all. FCC would care greatly if a company the size of Apple was selling a product that violated the emission limits.
That said, I don’t think this device violates the official limits. The author’s problem is that they need something extremely quiet, beyond the acceptable limits.
> If all the cheap switching power supplies and other devices were actually tested, almost none of them would be RF quiet (or even compliant).
If you’re suggesting that “almost none” of the power supplies on the market are actually compliant, you are incorrect. I’ve done my fair share of compliance testing. It’s true that you can find random supplies that aren’t compliant, but it’s not true that we’re all out here fudging test results and lying our way through certification. These things actually get tested.
If Kleenex gets into toilet paper and tell you that toilet paper is now kleenex, the response is "you clearly don't what what the hell you're talking about, get your head out your ass".
Magsafe is a magnetic power connector that clicks into a socket, whether Apple sticks their head up their ass or not.
That inrush current however, given sufficiently large buffer capacitors, can be enough to trip the overcurrent protection that most if not all RCDs also have - and that one tends to get more sensitive as they age, it's a common issue with old breakers.
(Another device that could trip is an arc-fault detection device, but AFDDs are fairly new and not required by many electrical codes. Nevertheless, it's a good idea to upgrade your distribution boxes with them, if you have the budget. These things save lives.)
An RCD will trip when the difference between the current going down the live and neutral conductors exceeds a certain value -- in normal operation they are opposite and cancel each other out.
If it operated how you describe, it could never detect someone touching a live conductor, because the current would not return through the ground prong.
Either way, it's certainly a problem with the computer - I've far more demanding equipment that has never done this, and have yet to find a circuit it won't *pop*.
I don't know anything about electronics. Do you think this is some kind of defect or bad design of the power supply?
Note that this author isn’t claiming the device breaks FCC limits, just that it emits enough that his highly sensitive radio could pick it up.
It’s not reasonable to be mad at a company for shipping a product that meets the limits. This guy just wanted something lower than the official limits because he’s tuning a radio to that frequency right next to it.
It's only a problem if it's a problem. If they'd done proper filtering inside the device maybe it's ok.
I had a long serial line strung across my desk from a USB-Serial dongle to an embedded board. It ran under the LCD monitor. Weird banding and noise was showing on the monitor.
The demo was: "watch the artifacts on the monitor go away, as I clamp this ferrite bead around the serial cable".
Why not notify the FCC ?
The author’s use case is relatively niche. The FCC limits aren’t designed to be so strict that devices can’t emit measurable radiation at all because that’s an impossible task.
The only reason the author is hearing it is because he is literally tuning a highly sensitive radio to that frequency and putting it right next to the device.
Moving either charger to a different ground potential removed the issue. There was probably a missing backfeed filter diode on a ground track or decoupling capacitor somewhere in the headphones' charging circuit.
The "gosh, this is hot" thing when its on charge has been an issue from time to time, as the magsafe ages out, or some component on the mac board. Apparently its caused by HF on top of the desired DC, leaking out the componentry somehow as mechanical vibration.
I think the periodic electric impulses may be interpreted by your brain as a fake stick-slip phenomenon and change how the texture feels.
See: https://superuser.com/questions/462244/electric-shock-mild-v...
https://www.amazon.de/Samsung-Powerbank-Capacity-Charging-In...
Perhaps (as the author says), the engineers could come up with something more elegant.
Isn’t that just two wraps? Or two and a half at best?
is there a guarantee that these frequencies weren't added in for some engineered purpose?
The end of this thing is a bunch of wire in a loop, the inductor that transfers the energy to the phone. So it was odd to me that he chose the cord as the antenna that was broadcasting the noise, when I'd think it would be the business end. These frequencies being broadcast might be overlooked harmonics, ok to filter out, but they might be a designed part of the energy transfer that the charger is attempting. It's possible that he's damped the noise and the charging, but under normal use he doesn't need the maximum charge so it's still a win.
not my specialty, just speculating based on basic EE knowledge.
So, no, this doesn’t slow down charging.
Honestly doesn't surprise me. I hold the same kind of sentiment after spending $1200~ on a brand new iphone 14 pro max just to find that I had to buy the charger brick so I could plug it into a wall. Come on Apple. Eliminating QOL things doesn't just automatically equal improvement.
Expecting every company to make their products ultra-quiet beyond the FCC limits so amateur radio operators can use them right next to their radios isn’t realistic. You certainly wouldn’t like paying the added costs of all of your products just to make them extra quiet for hams.
The author showed how easy it was for hams to solve their own problem as needed. Putting a ferrite on every charger in the world just to appease the handful of hams who want to use their radio right next to it is unreasonable.
Seems like the author resolved the problem at minimal cost and effort.
And as others have mentioned, Apple could have placed a small ferrite on the power supply PCB to achieve the same effect.
The author has different priorities but they're idiosyncratic.
Perhaps they should have made the charger optional... but completely agree overall with the decision not to include it.
The only argument is "well, then they should have dropped the price of the phone." Okay dropped it relative to what? "Obviously relative to last year's price." Why? There is/was heavy inflation and other products became more expensive but the iPhone didn't. At most you are complaining about shrinkflation.
I’m pleased Apple stopped adding enormous amounts of ewaste by not producing tens or hundreds of millions of these things every year for the majority of people who do not need them.
Or they could just include a 20 watt usb c charger with my $800-1200+tax and activation fees phone and not force me to spend another $60 on their power adapter. though to be fair a third party option would certainly be less expensive.
> Mix 31 excellent for 1-10 MHz common mode suppression, then about same as 43 up to 250 MHz, NOT recommended for multi-ratio impedance transformers (baluns/ununs) due to material characteristics and power handling capability – ok for ham radio 1:1 feed line choke applications. Curie temperature >130 C
But in looking for concise relevant information i found https://palomar-engineers.com/ferrite-products/ferrite-cores... which i quoted above
edit: also, thank you
The black ring is probably one of the "other pieces for my car mount".
I'm also just grown weary of amazon.
Also there was a possibly false tale of intel adding clock jitter years ago to spread the emi across a band to pass tests, and then forgetting to enable that jitter on production units.
Smaller, cheaper, lighter, better. Just hard to retrofit if they weren’t designed as part of the board to begin with.
The minimal effort included hours of studying electrical engineering and radio technology at university including all the math and physics needed. Studying for amateur radio license. And after founding this issue delving deep into radio interference literature and datasheets of various components. Then setting up a test environment to replicate the issue and do tests trying to eliminate the interference. After a success write a blog post describing the solution in short and hopefully interesting way.
I think it'd be great if Apple offered a small discount for opting out of unnecessary items.
Androids have their fancy ~100W fast charging where all of the charge controlling is in the brick for thermal reasons and those require special proprietary chargers that become obsolete after a generation, but Apple doesn't do that.
Also if the interference didn't come from the disc side of charger then the issue wouldn't be resolved with ferrite bead on that end. If the issue was on the USB connector side then the bead should be placed there.
Wikipedia on MagSafe (wireless charger)
> MagSafe is a proprietary, *magnetically attached* wireless power transfer
That probably means I can talk with my phone while wireless charger hangs on to the back of the phone?!
https://www.theverge.com/2020/10/13/21514480/apple-iphone-ch...
But, separated by a very large piece of conductive metal. (I think even carbon fiber planes have a conductive layer in there, to prevent damage from lightning strikes.)
Worst offender is you aren't using a ground plane or routing a return path. You might be under the impression that your signal travels on the copper you routed for the signal - it does not. It travels mostly in a magnetic field between your copper signal and the closest signal of largest difference. Which in your case is only sometimes going to be your ground trace.
Short version... I would not use this as any sort of example for RF performance, at all anywhere, ever, and I'm being a nice as possible on that. I bet if you made a quick loop with an oscilloscope it would off the charts in reality. This would never pass FCC background.
EDIT: I see this was 7 years ago, but I would not use that as an example. At a very minimum if you are still making circuits... Watch every Phil's Lab video from 1 to 100. But somewhere in 50s is a good one on stack ups and signal returns.
EDIT2: While I'm picking you apart, which you implictitly asked for, your board is HUGE. So who cares how large L1 and C12 are? On that note, I could almost not find L1 at all, the schematic is a bit of a mess. KiCad is great and now allows for global and bussed component blocks I would recommend. Again, there is a Phil's lab video on that.
There is no one ground. The 120VDC side has an HV ground, and the 5VDC side has a ground. The important point is to have separation between the two.
That is exactly one of the misunderstandings I’m trying to warn that you are missing.
I’m certain that your switching transition times are massively faster than the 300k period (each rise and fall time).
You can have split grounds, but you don’t have traces under your grounds so in many cases you aren’t even effectively using them. You are grounding a portion of every signal inside every other signal trace.
“The rest doesn’t matter much”… my man, I can’t explain in this form just how wrong you are.
It’s one thing to be wrong on a design from years ago. My old designs were worse. But it’s another thing to willfully ignore all the ways in which someone who knows better is trying to help you with.
Everything you think about that circuit is wrong in ways you aren’t getting - yet.
Try Phil’s lab videos for EMI.
It may be that this charger passes the legal requirements while still causing small amounts of interference when placed near a receiver.
Not really. Part of the FCC certification process is that devices need to accept interference from other devices operating within the limits.
Go read the FCC sticker on the bottom of any nearby device if you don’t believe me. It’s spelled out in the text.
The only reason the author had a problem is they put it right next to, quite literally, a highly sensitive receiver tuned to the exact frequency. It doesn’t mean the device was exceeding FCC limits, it means the ham operator needed to carefully set up their environment more tightly then even the FCC limits.
Note that only some classes of device have this requirement to accept all interference from devices operating within the limits. For some classes of devices if a consumer device interferes with then the consumer device's owner is responsible for stopping the interference even if the consumer device is operating entirely within limits.
The FCC regulations are divided into several parts, covering different devices and services. For example Part 87 covers various aviation radio services and devices, Part 97 covers Amateur Radio, and Part 20 covers mobile phones.
For any given frequency there might be devices or services covered under several different parts that can radiate on that frequency. There will generally be some kind of hierarchy among them where devices are not allowed to interfere with devices higher in the hierarchy and must accept interference from devices higher in the hierarchy.
The Part that covers much of consumer electronics other than mobile phones is Part 15. For most common consumer devices, if it is not a mobile phone and you did not need to get a license from the FCC to use it it probably falls under Part 15. This includes "intentional radiators", which are devices that are intended to emit radio such as WiFi routers, "unintentional radiators", which are devices that intentionally generate radio frequency energy within the device but it is meant to stay within wires or within the device, and "incidental radiators", which are devices that aren't intended to generate radio frequency energy but do so as a side effect such as DC motors and mechanical light switches.
Part 15 is at the bottom of the hierarchy.
For Part 15 devices, 47 CFR 15.5(b) says:
> Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.
Other Parts can have quite different rules. For example Part 95 Subpart C, which covers radio control such as is commonly used in RC models, says this:
> (a) RCRS stations must not cause interference to:
> (1) Authorized radio operations in the 72–76 MHz band, including radio remote control of industrial equipment on the same or adjacent channels; or,
> (2) Broadcast television reception on TV Channels 4 or 5.
> (b) RCRS operations are not afforded protection from interference caused by the operation of:
> (1) Industrial, scientific or medical devices (see part 18 of this chapter) operating in the 26–28 MHz band; and,
> (2) Fixed and mobile stations in other services operating on the same or adjacent channels.
For Amateur ("ham") Radio, the interference rules are much more extensive, because hams are authorized to use a lot of frequency bands that overlap other services. Here's a link if anyone is curious [1].
Comparing to a broadcast FM station, the strength of the RFI as observed by any nearby radio will be trivial by comparison. Broadcast stations are some of the highest-power radio transmissions around us, typically thousands of kilowatts (for example the rock station near me transmits at an ERP of 51,000 watts[0]). You will hear this station clearly no matter what kind of nearby RFI is present, and the receiver's AGC will reduce RF gain to probably as low as it goes. By comparison, amateur radios typically operate in the range of 5-100 watts. Thus you might gather that comparing localized RFI to broadcast stations is not a meaningful comparison.
I don't think so.
Not "thousands of killowatts" transmitted. Your example is as you say, an ERP of 51kW.
But even ERP doesn't refer to the transmitter. An ERP of 51,000W is most likely a 5-10kW transmitter, with a gain factor of 5-10.
Back in the '30s a few AM stations ran at 500kw, and could be picked up on other continents.
Or, taking a notoriously powerful FM radio station like KRUZ 103.3, it would be like hearing that station from perhaps 300,000 kilometers away.
Most loss is not free-space loss though - it's due to reflections from man made objects and absorption into the earth that results in line-of-sight effects at these frequencies.
I often look at the automated reports and look sadly at the 99% of stations that can hear me but that I can't hear.
Avoid sinking a lot of money into a transceiver immediately before you've been operating for awhile and know what you're really interested in doing. You also do not need a rooftop antenna for HF (3-30 MHz; the frequencies that most often travel far) - a wire across your backyard can be quite effective.
Since you're here, I recommend getting started with digital modes like WSPR and FT8. They require a lot less power to make some surprising connections, and will teach you a lot about how propagation works and adjusting antennas, and because of the low power requirements, can be done with relatively inexpensive equipment. Some "old timers" grouch about how they're not "real" ham radio, but ignore them.
Edited to add: A good starting point that doesn't even require a license is to get an SDR receiver like the RTL-SDR and hook a long wire to it as an antenna, then listen for WSPR or FT8 signals with WSJT-X, and whatever else (other digital modes, Morse Code) with fldigi.
Then out of no where it's talking about tantalum nitride...
No, I'm pretty sure that video was made by an AI.
I was just replying to the above comment which could read “a little noise from a single device isn’t a big deal.”
It is definitely up to regulators to decide what is acceptable, and up to Apple to meet those regulations. It’s still a little unclear from the OP whether or not the spurious emissions meet transmission requirements, but it definitely a good place to do further lab tests for compliance.
Do bodies like the FCC independently verify compliance?
