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Can wireless charging phone holders interfere with avionics?

I am sure that mobile phone makers pull every trick to reduce emissions. It was always the case that an old Nokia 6310i would pick up a weak signal long after every smartphone became useless and I am sure it is still the case today. Today’s phones don’t have to be that good; most people live their entire life in a good signal area now. Mostly old people live in the countryside But they still have to be reasonable.

Many years ago, spread spectrum came in. Those setting the compliance standards, and predictably those running the €2000/day compliance test labs got very agitated about this and started planting articles in the tech press that this will be banned by the EU next year, etc. That was fiction/FUD (it cannot be banned) and we still have spread spectrum, widely used in IT products. It makes the spikes lower and fatter, and there is no regulation on fatness But it helps only a bit; it won’t give you a 40db drop.

Sinewave generation is easy enough to do. You can do it using PWM and filtering it, by feeding a sine lookup table into a DAC, by generating a sawtooth and filtering it, etc. But that dissipates power in the amplifier driving the coils. The better approach is to sine-modulate a switching power supply, which could be done totally analog, or with some micros which are fast enough.

But this wireless charger was about £20 which means the manufacturing cost must be below about £5, so they couldn’t care less… If I was to use it in the plane I would rebuild it with a decent circuit, but is wireless charging totally passive, with no “data” passed? I haven’t looked into it. USB (cable) charging is quite an involved protocol, to handle the various incompatible approaches from Apple and the others.

Administrator
Shoreham EGKA, United Kingdom

The font on that analyser makes my eyes bleed! Why on earth are the lower case a’s bigger than all the other lower case letters (!)

Various manufactures do eval kits for Qi chargers.

This ST Microelectronics one is available from Farnell / Mouser / Digikey etc.

STEVAL-ISB027V1

The font on that analyser makes my eyes bleed! Why on earth are the lower case a’s bigger than all the other lower case letters (!)

As they say, in the land of the blind, the one-eyed man is King, and in this case the man with a spectrum analyser is the King. I paid about 1k for that in 2014, used, which was a fraction of what they would cost new. It’s got quite a high spec.

This ST Microelectronics one is available from Farnell / Mouser / Digikey etc.

Looking at the price of the STWBC chip I doubt any chinese products use that. But it does look like a square wave drive thing, with a capacitor to create a sort of resonant circuit.

Anyway, a DIY implementation looks like a lot of work.

Sometimes things move backwards, and the USB-C connector is much less suited (due to its high insertion force) to phone holders than the micro-USB, or the old Iphone/Ipad wide one.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Sometimes things move backwards, and the USB-C connector is much less suited (due to its high insertion force) to phone holders than the micro-USB, or the old Iphone/Ipad wide one.

Strange – even with my rheumatic hands I have zero problems with this

EHLE / Lelystad, Netherlands, Netherlands

I think the issue you’ll have with the wireless chargers is not so much the radio’s antenna picking up the splatter (it doesn’t go very far, as Peter shows, and probably won’t reach the antenna in a way that will matter) but rather if the splatter gets out up the power input of the charger and into the aircraft’s electrical system. Noise getting out on the supply is a problem with quite a few cheap devices. But this is generally fixable with ferrites.

Last Edited by alioth at 24 Apr 09:07
Andreas IOM

Yes; conducted RFI is pretty likely. It’s not that easy to filter however in the aircraft scenario because you fix one path and the muck p1sses out of another hole.

I have spent a lot of time on this, in years past, having built various multi output power supplies for tablets (especially in the days before most things would run off USB 5V) and then found it totally wiped out some VHF frequencies. Luckily one of these was the Shoreham tower one so I found it immediately. I then built totally OTT filters for the DC input, shielding the cable, etc, but they didn’t do enough.

I had more problems with a satphone car holder (here – search for sattrans) which radiated like Chernobyl and no amount of line filtering (in a diecast box underneath the car holder) was enough to make VHF comms work. I had to abandon that project because of that. It was a private project – basically a version of what is today the Golze ADL but running over Thuraya dial-up, and doing just textual stuff.

Basically the designers of some of this car stuff are clueless. There are well known approaches e.g. multiphase PWM on which the ripple cancels out (first order) and this deals with a raft of issues in one go. Run it at say 1MHz (have to if you want small ferrites and small ceramic caps) and there won’t be any emission below 1MHz The phone makers know all this and do it right, otherwise their phones wouldn’t work.

Administrator
Shoreham EGKA, United Kingdom
17 Posts
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