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Characterizing interference from USB chargers


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3 hours ago, 0TreeLemur said:

@EricJ  nice thread and I enjoyed your pdf article.  Do you think a SDR setup could be used to do the spectrum analysis as you did, or would it be too noisy?   It seems that if the antenna is as far way from the computer as possible and near the USB adapter it might work?  Thx.

Yeah, you can do stuff like that.   There's already off-the-shelf stuff and software to do things like that.   Today even very good, bench-quality spectrum analyzers are USB units that plug into a laptop or desktop.   RTL-SDR dongles have been around for quite a while and have a very wide tuning range, so they can sense the local radiation environment and then be used for analysis on a laptop or an RPi or whatever.    Do a web search on "RTL-SDR spectrum analyzer" and there's a bunch of stuff (mostly free) that can be used for some quick basic analysis.   The RTL-SDR dongles are about $20 these days, and sometimes come with an antenna or two.   If you're worried about VHF interference, just get a little VHF antenna for it and go from there.

These days if I'm doing reasonably serious bench or field work I usually use stuff from these guys, but it's a lot more of an investment than $20 for a dongle and d/l some free software.  ;) Still just a USB device that plugs into a 'puter, though:

https://signalhound.com/

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1 hour ago, Gagarin said:

The USB adapters employ switching regulators to increase the dynamic range and reduce heat. You can reduce the noise they generate by putting them in the linear mode by adding a resistor in series at the cigarette lighter input. The resistor would be about 27 ohms/1 watt but it may vary depending on the load and whether your plane is 12v or 24v.

Interference is sometimes coupled through the power bus. For this case try a 1000mfd/50v capacitor connected in parallel to the cigarette lighter input. 

I've no idea what you might've meant, but most of what you wrote doesn't make much sense and either isn't correct or isn't a good idea, imho, anyway

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19 minutes ago, EricJ said:

I've no idea what you might've meant, but most of what you wrote doesn't make much sense and either isn't correct or isn't a good idea, imho, anyway

Don't worry Eric it was not intended for your superior intellect.

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  • 4 months later...

*UPDATE*

Brice, @ragedracer1977, loaned me a couple in-panel units that he had laying around, including one with appropriate certifications, so I thought I'd break out the spectrum analyzer again and see what I could see.   Be warned that the doc is like last time, only this time it is twelve pages of nerd-speak instead of just seven.   There are still pictures and plots, too, for those unenamored of my prose.

Executive summary:

Pretty much all of the units are very quiet except the same ones that were noisy the last time, i.e., the units with the voltage/load/temperature display.   The unit that has a CO detector in it didn't work this time, but I included the results for it from last time that show it's pretty quiet, too.   The very expensive, certified unit was also quiet, as was a very nice, non-certified unit that is popular with homebuilders (experimental).   I also include some discussion about the non-relevance of the certifications from an rf interference point of view.

Doc here:   http://ericjacobsen.org/Files/USB_Power_Supply_RF_analysis_3.pdf

These were the units tested:
image.png.f6dcd3131663bf6cf53c07a62d58c07e.png

The two on the left are the crappy ones (which I fly with regularly and don't cause problems), and the rest are very quiet.   The right-most one is the Appareo TSO'd unit that Aircraft Spruce sells, and they also sell the Blue Sea Systems marine unit next to it that is popular with homebuilders.   The Blue Sea unit has device detection capability so that it can presumably do smart-charging to connected devices.   On my Galaxies (tabs and phones) this often means a 15-20 minute charge to full instead of a couple of hours.  This is also a marine unit with a conformal-coated circuit board, etc., i.e., you get something for the extra money.   Amazon sells a round, lighter-socket fittable version that I think I'm gonna try:

https://www.amazon.com/gp/product/B01BV1MTAA/

My personal opinion/conclusion is that the TSO/RTCA certs get you next to nothing either from a standards or performance perspective for interference mitigation.   Neither standard provides confidence that a compliant unit won't cause interference.   A very cheap unit like the white Wells Fargo-branded model is already essentially as quiet as the more expensive units, and with twenty-cents worth of shielding could be essentially guaranteed to suppress radiation.   It may already have some, I don't know, because I didn't take any of them apart.

The Blue Sea Systems units:   

https://www.bluesea.com/products/1039/12_24V_Dual_USB_4.8A_Chargers_-_Switch_Mount

https://www.bluesea.com/products/1045/12_24V_Dual_USB_4.8A_Chargers_-_Socket_Mount

Anyway, just some additional info for Those Who May Care.

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11 hours ago, EricJ said:

*UPDATE*

Brice, @ragedracer1977, loaned me a couple in-panel units that he had laying around, including one with appropriate certifications, so I thought I'd break out the spectrum analyzer again and see what I could see.   Be warned that the doc is like last time, only this time it is twelve pages of nerd-speak instead of just seven.   There are still pictures and plots, too, for those unenamored of my prose.

Executive summary:

Pretty much all of the units are very quiet except the same ones that were noisy the last time, i.e., the units with the voltage/load/temperature display.   The unit that has a CO detector in it didn't work this time, but I included the results for it from last time that show it's pretty quiet, too.   The very expensive, certified unit was also quiet, as was a very nice, non-certified unit that is popular with homebuilders (experimental).   I also include some discussion about the non-relevance of the certifications from an rf interference point of view.

Doc here:   http://ericjacobsen.org/Files/USB_Power_Supply_RF_analysis_3.pdf

These were the units tested:
image.png.f6dcd3131663bf6cf53c07a62d58c07e.png

The two on the left are the crappy ones (which I fly with regularly and don't cause problems), and the rest are very quiet.   The right-most one is the Appareo TSO'd unit that Aircraft Spruce sells, and they also sell the Blue Sea Systems marine unit next to it that is popular with homebuilders.   The Blue Sea unit has device detection capability so that it can presumably do smart-charging to connected devices.   On my Galaxies (tabs and phones) this often means a 15-20 minute charge to full instead of a couple of hours.  This is also a marine unit with a conformal-coated circuit board, etc., i.e., you get something for the extra money.   Amazon sells a round, lighter-socket fittable version that I think I'm gonna try:

https://www.amazon.com/gp/product/B01BV1MTAA/

My personal opinion/conclusion is that the TSO/RTCA certs get you next to nothing either from a standards or performance perspective for interference mitigation.   Neither standard provides confidence that a compliant unit won't cause interference.   A very cheap unit like the white Wells Fargo-branded model is already essentially as quiet as the more expensive units, and with twenty-cents worth of shielding could be essentially guaranteed to suppress radiation.   It may already have some, I don't know, because I didn't take any of them apart.

The Blue Sea Systems units:   

https://www.bluesea.com/products/1039/12_24V_Dual_USB_4.8A_Chargers_-_Switch_Mount

https://www.bluesea.com/products/1045/12_24V_Dual_USB_4.8A_Chargers_-_Socket_Mount

Anyway, just some additional info for Those Who May Care.

Wow! Nice work!

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  • 1 year later...

I had a Skiva charger for a few years that I found via a link on another post somewhere.  It didn't introduce any static, and worked great for the few times I used it.  Unfortunately, I tried to use it a couple weeks ago and it blew the fuse to the cigarette lighter in my 231.  After landing I tried to plug it into my Tundra, and it blew the fuse there too.  Then I went on a search for other options, mostly because I felt the Skiva was a pretty cheaply made plastic POS.  After a bit of research, I tried using a charger that I already owned with an Apple cable that was wrapped around a ferrite core, and there was no difference...a ton of static in my com radios.  I finally found a post that referenced an Anker IQ charger that somebody had luck with.  I came close to buying that one, but liked the smaller form factor in this one better: https://www.amazon.com/gp/product/B07PGT7LSR/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1  I tested it today, and had absolutely no static in my com radios.  Hopefully this helps someone that is in the same search as me.

 

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