[Animats]

> This radio interference was also present on the aviation frequencies (around 124 MHz)

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...

[NovemberWhiskey]

>How did this thing get FCC approval?

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.

[amatecha]

I use HF radio all the time from inside my home, in the middle of one of the densest cities in BC. Within the past few weeks I've made contacts with stations in Alaska, Belize, Costa Rica, Colombia, Russia and Japan with a radio inside my home in Vancouver, Canada. HF is 10000% usable in urban areas. It's not optimal or perfect, but it's just fine.

[jrockway]

Making the contact is easy (the interference you hear doesn't exist at the receiver), hearing the other end is hard. Most of my indoor QSOs are people running 1500W FT8 which is ... an unnecessary amount of power. (Meanwhile, I'm sitting here transmitting at 3W.)

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.

[amatecha]

Yup, RX harder than TX in the city, that's for sure. I'm thinking to set up a "loop-on-ground" antenna[0] for RX which, from anecdotes I've heard from people I know, takes their S8 noise floor to like S1.

[0] http://www.kk5jy.net/LoG/

[jrockway]

I should definitely set something like that up. I have a patio now and this would be unlikely to annoy anyone above me looking at my patio and reporting it to the board. (Not that I think my neighbors would care, but it's a common complaint against hams.)

[NovemberWhiskey]

Sure. Right now, we're coming towards the top of a sunspot cycle that results in SFI levels not seen in 20 years. Let me know how you were doing in 2019. There's obviously a seasonal overlay here.

[amatecha]

I wasn't an op in 2019 -- got my certification in 2022. That said, I used to receive FT8 with my RTL-SDR and have a few screenshots. Here's a map of my received signals on 40m, overnight in May 2020, with a random-wire antenna: https://i.imgur.com/flfyIZx.png At that time I lived in an even more densely-populated area (a condo complex with over 100 units, on a main street, surrounded by other similarly-large condo complexes).

[jrockway]

Oh man, I haven't been paying attention to the sunspot cycle. I got my license at a low and committed to being depressed about it forever, but ... time fixes everything I guess!

[threeio]

its still doable in 2019... just not as plentiful ;) I was still able to get DXCC during the lows in a Silicon Valley downtown tiny lot (however, this isn't an apartment in a major city)

[asdefghyk]

Would not a persons specific setup have significant effect on the interference situation, - The radio would be in a completely shielded metal box? - so no interference that way directly , not via the antenna input. Outside antenna , with a shielded feed in cable would also reduce interference from these devices like small power supplies that just produce interfearance to a few meters distance ???

[kaishiro]

As someone who has always been interested in getting into ham radio - do you have any pointers on where to start or what to avoid?

[MandieD]

First of all, get your entry-level license. If you're in the US (or have someone who can receive mail for you), this is relatively easy and inexpensive, and can be done completely online.

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.

[matthews2]

Join a local club!

[t0mas88]

Near-field being as big as 2 meters from the charger can be quite relevant for use in aircraft. Since on a narrow-body aircraft passengers can easily be within 2 meters of some of the VHF antennae.

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.

[jrockway]

> Since on a narrow-body aircraft passengers can easily be within 2 meters of some of the VHF antennae.

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.)

[skykooler]

Isn’t carbon fiber conductive itself?

[thenickdude]

Yes, and blocks radio transmissions very nicely. When making a model airplane with a carbon fibre hull, we have to add a plain fibreglass or plastic window for the antenna to receive through.

[tonyarkles]

Carbon fibre is definitely conductive. A couple of years ago I measured a 1” diameter tube and got about 15ohms/ft.

[Animats]

Right, it's a resistor. This is a problem for airframes and wind turbine blades. Its resistance is too high to deal well with lightning. So aluminum is needed to provide a conductive path.

[crote]

Do you have any idea how that power compares to regular FM radio broadcasts, which are somewhat close in frequency?

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?

[amatecha]

Due to proximity, the interference from the charger is comparable to what the receiver was expecting from a normal signal (like an amateur radio repeater or fellow operator's station), which is why his radio broke squelch while scanning. Because the radio is relatively close to the charger, the RFI is picked up quite well.

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.

[0]https://en.wikipedia.org/wiki/CFOX-FM

[FireBeyond]

> 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]).

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.

[TylerE]

Back in the pirate radio days 100 and 250kw transmitters were common.

Back in the '30s a few AM stations ran at 500kw, and could be picked up on other continents.

[FireBeyond]

AM? Definitely, but even that is 100, 250, 500. Not "thousands of kW".

[amatecha]

Oh sorry, I doubled up my units of measurement there, yes, tens of kilowatts haha :) (unfortunately too late to be able to edit that comment)

[NovemberWhiskey]

To get a very broad idea: if you had perfectly efficient but isotropic antennas (you don't) this would be about the power level you'd get receiving a typical 3W hand-held radio signal at 140MHz from 1,000 kilometers away. This is why you can talk to the International Space Station easily enough with vanilla ham radio equipment.

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.

[amatecha]

How did you come to that estimation? The strength of the RFI on the waterfall suggests received signal strength comparable to someone transmitting on a 5w HT within, say, 5-10 miles (aka not in the immediate neighbourhood, but pretty nearby). Someone transmitting 3w at 1000km distance will not register even the slightest on any amateur receiver, even with RF gain absolutely cranked to the max and with a massive antenna.

[NovemberWhiskey]

I actually updated my post about the same time you wrote this response; I was just considering free-space path loss, which is not where most of the loss is in typical ham scenarios. Most of the 5W in the case you described is getting lost in a terrible compromise antenna, then due to line of sight effects (assuming that the user is not standing on a hill or something) and multipath.

[TylerE]

The ISS also orbits quite low. If you're relatively close to the path it's only a few hundred miles away. Small temporal window due to the speed, but still.

[js2]

I can't be sure this is the exact model as OP, but the FCC testing doesn't seem to indicate any issues from my brief skim:

https://fccid.io/BCGA2548

(I have not read the entire report and I have no expertise in RF.)

[Mistletoe]

Is the original author certain he has an authentic Apple charger? I’ve seen teardowns many times of bogus Apple chargers that use worse designs and components.

http://www.righto.com/2016/03/counterfeit-macbook-charger-te...

[wkat4242]

Yeah and the external wire will act like an antenna especially if it's got the right length.

Very bad. Strange also because Apple usually gets their PSUs made by Delta afaik and they are as good as it gets.

[colechristensen]

It’s not very bad. Detectable signals is not at all equivalent to interference.

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.

[amatecha]

Breaking squelch on a scanning radio in the general vicinity is pretty bad. It shouldn't be generating such strong RFI on VHF frequencies. I use 2m (VHF) handheld radios at my desk at home with like 5 computers around me, countless chargers (including a wireless charger just like in the article). There is never a time that my radios are stopping on RFI generated within my office.

[galangalalgol]

When people ask for certification. The stuff you get on amazon now doesn't have FCC numbers. Or silk screening on the pcbs or components to identify them.

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.

[SV_BubbleTime]

>The power in the USB cable is DC. There shouldn't be any significant RF component.

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.

[Animats]

You don't have to let the spikes from the switcher get very far.

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...

[SV_BubbleTime]

Oooh. I clicked through your PCB there. I would highly recommend you read a couple books on circuit design. You have a 2 layer PCB with no ground plane and you aren't routing ground, signals passing parallel with each other on adjacent layers, you have mixed analog and digital domain, massively long traces where they could be shortened with a small jumpers.

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.

[Animats]

Nothing there is going faster than about 300KHz, so the signal paths are not a big issue. If things had to go faster, there would be a proper ground plane. The tiny area around the switching IC did require careful layout (it just follows the Linear Technology data sheet) but the rest doesn't matter much.

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.

[SV_BubbleTime]

> nothing faster than 300k

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.

[xeonmc]

off topic, but what do you think of this video by Asianometry talking about the intricacies of analog design for a laymen audience? https://www.youtube.com/watch?v=lNypq1XuZRo

[genewitch]

Even very expensive linear supplies will have Vpp of a few millivolts or microvolts "ripple". Vpp is voltage peak to peak, which you wouldn't expect on a DC device, but there you go.

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!

[mtreis86]

This, for reference see the book High Speed Digital Design by Hall Hall and McCall https://archive.org/details/highspeeddigital0000hall/ The sharper the edge of the digital pulse, the greater the strength of the AC high frequency components. A perfect square wave is the sum of the infinite series of odd harmonics of a sine wave with the same wavelength.

[SV_BubbleTime]

I watched a video recently that had another author describe issues in a way that I found very intuitive. https://www.youtube.com/watch?v=kdCJxdR7L_I

[wglb]

Switch mode power supplies such as this one emit RF. There are varying degrees of shielding that can help, but ham radio stations that are looking for good reception forbid using any such chargers (e.g., iPhone charger, Macbook chargers, etc).

Far better to use a linear power supply, which has a transformer and as a result is far heavier.

[marcinzm]

>If RF got outside the charger and into the USB cable, it's very badly designed

Wouldn't this then be a problem with whatever car charger he is using and not with the apple device plugged into that charger?

[rajnathani]

Could the problem be with the DC current that is being supplied via USB power from the car / power adapter? If this DC current is very noisy, then it could make the noise generated worse I presume?

[jve]

> a pilot charging an Ipad in an aircraft.[1]

Fascinating. No wonders we have so much red tape on stuff that is in the air.

[numpad0]

Well, modern DC converters use PWM, and also the device in question is a Qi induction charger operating at 110 - 205kHz with up to 15W output so there is some significan- how are these unlicensed!?