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Eliminating radio interference from Apple charger

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Re: Eliminating radio interference from Apple charger

#61

Post by amatecha »

crote wrote: post #53
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 (…

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?

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

Re: Eliminating radio interference from Apple charger

#62

Post by mtreis86 »

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.

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.

Re: Eliminating radio interference from Apple charger

#63

Post by amatecha »

NovemberWhiskey wrote: post #54
crote wrote: post #53

Earlier quoted context omitted.

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?

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 heari…

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.

Re: Eliminating radio interference from Apple charger

#64

Post by amatecha »

colechristensen wrote: post #55
wkat4242 wrote: post #16

Earlier quoted context omitted.

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.

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.

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.

Re: Eliminating radio interference from Apple charger

#65

Post by genewitch »

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.

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!

Re: Eliminating radio interference from Apple charger

#66

Post by genewitch »

gorkish wrote: post #45

I'm quite frankly amazed that this is the first time this guy has had to put a choke on something as a radio amateur. I guess he doesn't use HF that much otherwise he'd probably have opted to buy an entire bag of ferrites. 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 wo…

where can one buy a bag of ferrites?

Re: Eliminating radio interference from Apple charger

#68

Post by pnpnp »

Clamchop wrote: post #60
pnpnp wrote: post #43

Earlier quoted context omitted.

There’s also a big difference between one charger emitting some noise, and a couple million in a big city raising the noise floor for the frequency.

It's not Apple's job to determine if there's a problem with that and regulations on this issue are, so far as I'm aware, treated very seriously.

Sorry - I can clarify a little. If it complies with regulations, Apple is definitely not at fault.

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.

Re: Eliminating radio interference from Apple charger

#69

Post by NovemberWhiskey »

amatecha wrote: post #63
NovemberWhiskey wrote: post #54

Earlier quoted context omitted.

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 heari…

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 anten…

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.

Re: Eliminating radio interference from Apple charger

#70

Post by urlgrey »

genewitch wrote: post #66
gorkish wrote: post #45

I'm quite frankly amazed that this is the first time this guy has had to put a choke on something as a radio amateur. I guess he doesn't use HF that much otherwise he'd probably have opted to buy an entire bag of ferrites. 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 wo…

where can one buy a bag of ferrites?

There are several options from Amazon, try searching for "Clip-on Ferrite Ring".
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