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.
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.
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.
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.)
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?
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.
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 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.
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.
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...
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.
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.
> 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
I'm also just grown weary of amazon.
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.
The black ring is probably one of the "other pieces for my car mount".
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.
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?!
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?
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.
Smaller, cheaper, lighter, better. Just hard to retrofit if they weren’t designed as part of the board to begin with.
Seems like the author resolved the problem at minimal cost and effort.
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.
And as others have mentioned, Apple could have placed a small ferrite on the power supply PCB to achieve the same effect.
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.
The author has different priorities but they're idiosyncratic.
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.
Perhaps they should have made the charger optional... but completely agree overall with the decision not to include it.
https://www.theverge.com/2020/10/13/21514480/apple-iphone-ch...
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.
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.
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.
