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Qi wireless charging

Posted: Tue Sep 25, 2018 10:15 pm
by JEL
I read that Qi wireless chargers operate between 100-205 kHz and emit at 5-10 Watts.

Putting up several of those around your SDR... could they be the possible cause of USB connection issues?

I have 3 running, and I assume they broadcast continuously (Since they begin charging a device as soon as it is placed in the holder. There's no physical contacts, at least none visible, between the device and the charging pad. Only the EM field)

And since putting them up I have had the SDR, that sits at the end of a 10 meter long USB cable (Two 5-meter cables, one is powered (From the USB port, not external power source). Technically over the 5-meter limit of USB, and I can't run the Airspy on that cable, but the 'cheap' SDR is just lean enough on the data throughput for it to normally work without the connection being dropped), drop out several times.

SDR# just stops and I have to press the play button to get the SDR running again. It doesn't crash, it just acts like the stop-button was pressed.
When I try the Airspy on that cable it won't even begin to play (And if it does it stutters wildly and stops within seconds)

So, could those 3 Qi wireless chargers possibly be what puts the noise/interference over the limit for the 10 meter USB cable, and be the cause for SDR# simply stopping?

I have been running this long USB cable for over a year without issues, until now where the Qi wireless chargers have been put in use.

I recorded a 30 second video of the spectrum between 100-200 kHz (With no filters to block that area, and with a long-wire antenna running along the floor inside. The antenna is not actually near any of the chargers. The closest it gets is within about 1.5 meter (4-5 feet) to one of them)

I get a signal around 125 kHz, but it doesn't appear to be a very strong signal (The chargers claim to broadcast at 10 Watts, but I don't know if they can alter their power in any way)

I'm not sure it IS the wireless chargers that generate that signal though, because I have an LED TV that generates a ton of noise all the way up to over 10 MHz (With a very prominent signal around 75 kHz that looks a lot like the signal I get here at 125 kHz), so there's a chance this new signal could come from a neighbor instead of the chargers perhaps.

Anyway, I'm asking here in case others have already 'been there', so to speak :)

Re: Qi wireless charging

Posted: Wed Sep 26, 2018 1:32 am
by rtlsdrblog
Is the charger connected to your PC? It might just be that it's taking too much power away from the RTL-SDR and Airspies?

Re: Qi wireless charging

Posted: Wed Sep 26, 2018 1:28 pm
by JEL
rtlsdrblog wrote:
Wed Sep 26, 2018 1:32 am
Is the charger connected to your PC? It might just be that it's taking too much power away from the RTL-SDR and Airspies?
The signal in the video turns out NOT to be related to the chargers. I don't know where that signal came from, but my guess currently is that it's a neighbor's TV (I base that on the fact that it looks like the signal I get from my own TV, and that the neighbors were home when I recorded that video, and how strong it was compared to the one from my own TV. I can't confirm that it's from a TV though, but at least it's not from the chargers)

Currently there is no signal anywhere between 100 and 200 kHz that seems to be charger related.

No, the 3 chargers each have their own wall-socket power-supply (Those typical transformers that are used for pretty much all devices these days), so they're not connected to the computer in any way.

They are also not placed close to the computer. The closest one is about a meter (3 feet) away from the PC desktop-box (on the table where I got the monitors and keyboard)

So it appears they don't radiate any significant radio-signals (at least not at the frequencies where I have looked)

I'm wondering if perhaps it could be some windows update that changed something. It's a windows7 PC and it still gets those automated updates every few weeks. Perhaps one of those messed something up.

I will keep an eye on it and see if I can find a pattern.

Thanks for replying :)

Re: Qi wireless charging

Posted: Thu Sep 27, 2018 11:16 pm
by JEL

It seems it was indeed interference from one of the wireless chargers that was the cause of the trouble.

I took one charger out of service for the day, and so far there has been no problems running the SDR.
(It's just one day of testing, so obviously a thin basis to really conclude anything on. But at least it points to the charger as being the cause. I will do more testing of this and hopefully a repeatable pattern will emerge)

I suppose I should try to find the frequency or frequencies the charger actually uses, although I'm not sure if I can (I'm not sure what to look for and I didn't find anything at the frequencies Google says are used by the Qi-WirelessCharging standard)

But I'm probably not the only one facing issues with this relatively new wireless technology.
As Pink Floyd might have sung it: "just more noise in the wall" :) (The noise-wall that blocks the signals we DO want to hear)

Re: Qi wireless charging

Posted: Fri Sep 28, 2018 6:56 pm
by JEL
Further update:

Apparently it is not the wireless charger that cause problems :(

I had a disconnect again even when it was OFF.

I'm leaning toward it being due to neighbor-interference instead.
They have been doing a lot of construction work in the room (a bedroom) just above where the SDR and antenna is placed, so perhaps they installed something like lights or a television or something else that may cause considerable EM-interference. I can't think of any other reason now.

Apartment-life really is not very compatible with this hobby.