Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Eliminating radio interference from Apple charger

oh8hub.substack.com

Post reply on HN
Print view View original

71–80 of 179 posts

Re: Eliminating radio interference from Apple charger

#71

Post by amatecha »

NovemberWhiskey wrote: post #51
Animats wrote: post #10

> 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 po…

> 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 (…

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.

Re: Eliminating radio interference from Apple charger

#72

Post by Animats »

SV_BubbleTime wrote: post #38
Animats wrote: post #10

> 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 po…

>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.

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...

Re: Eliminating radio interference from Apple charger

#74

Post by sigmar »

NegativeLatency wrote: post #2

I wonder if someone suggested this at apple and was overruled because a bulky ferrite would "look bad"

The "bulky ferrite" he used is an easy 'hack.' the correct way to fix this wouldn't be as expensive or as bulky, as noted in the article: "I expect Apple could solve this problem with much cheaper and hidden it somewhere cleverly."

Re: Eliminating radio interference from Apple charger

#75

Post by t0mas88 »

NovemberWhiskey wrote: post #51
Animats wrote: post #10

> 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 po…

> 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 (…

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.

Re: Eliminating radio interference from Apple charger

#76

Post by NovemberWhiskey »

amatecha wrote: post #71
NovemberWhiskey wrote: post #51

Earlier quoted context omitted.

> 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 (…

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.

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.

Re: Eliminating radio interference from Apple charger

#77

Post by jrockway »

t0mas88 wrote: post #75
NovemberWhiskey wrote: post #51

Earlier quoted context omitted.

> 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 (…

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.

> 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.)

Re: Eliminating radio interference from Apple charger

#78

Post by SV_BubbleTime »

Animats wrote: post #72
SV_BubbleTime wrote: post #38

Earlier quoted context omitted.

>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.

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…

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.

Re: Eliminating radio interference from Apple charger

#79

Post by jrockway »

amatecha wrote: post #71
NovemberWhiskey wrote: post #51

Earlier quoted context omitted.

> 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 (…

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.

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.

Re: Eliminating radio interference from Apple charger

#80

Post by jrockway »

NovemberWhiskey wrote: post #76
amatecha wrote: post #71

Earlier quoted context omitted.

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.

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.

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!
Post reply on HN