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Transmit Radio Signals via Ethernet

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Re: Transmit Radio Signals via Ethernet

#21

Post by londons_explore »

4gotunameagain wrote: post #19
coderjames wrote: post #10

Please don't try this at home! 118 MHz - 137 MHz is a protected Aviation band across the globe for airplanes to communicate with air traffic control. We already have enough industrial noise problems in this band; please don't contribute to pollution of protected spectrum. You will be interfering with the safe operation of the airspace. See: https://en.wikipedia.org/wiki/Airband

This does not magically increase the power radiated by an ethernet cable or somehow change the base frequency of the interference. Furthermore, the power levels are very low. If you check the link at the bottom, he is using a directional (Moxon) antenna to receive this faint signal. If this could somehow pose an issue with anything, it would have been caught in EMI testing of all network equipment sold

EMI testing only tests a product during typical use.

It's very possible to transmit illegal power levels with software mods, or even carefully crafted data packets in some cases.

Re: Transmit Radio Signals via Ethernet

#22

Post by JosephRedfern »

4gotunameagain wrote: post #19
coderjames wrote: post #10

Please don't try this at home! 118 MHz - 137 MHz is a protected Aviation band across the globe for airplanes to communicate with air traffic control. We already have enough industrial noise problems in this band; please don't contribute to pollution of protected spectrum. You will be interfering with the safe operation of the airspace. See: https://en.wikipedia.org/wiki/Airband

This does not magically increase the power radiated by an ethernet cable or somehow change the base frequency of the interference. Furthermore, the power levels are very low. If you check the link at the bottom, he is using a directional (Moxon) antenna to receive this faint signal. If this could somehow pose an issue with anything, it would have been caught in EMI testing of all network equipment sold

Does EMI testing consider "atypical" uses like this one? I'd assumed that they only tested normal use cases. I'd consider (wrongly, perhaps?) changing speed of a NIC several times per second to be an atypical use.

Re: Transmit Radio Signals via Ethernet

#23

Post by PragmaticPulp »

Clever hack, but a lot of people are misinterpreting what’s going on here. These devices emit some very low level of 125MHz energy during normal operation. This software is simply turning that on and off, but not doing anything to increase the amount of emissions.

Presumably the 125MHz emissions are within the FCC allowed envelope anyway, so this isn’t doing anything to exceed normal emissions limits. This only works in a quiet RF environment, as noted in the README.

There is no need to be concerned about this signal reaching aircraft or otherwise interfering with normal transmissions.

Re: Transmit Radio Signals via Ethernet

#24

Post by [deleted] »

avian wrote: post #18
zsellera wrote: post #3

As someone recently participated in an EMC measurement, I really don't understand how anyone passes these tests without some kind of cheating (using double-shielded, very expensive industrial cables + hacking with functional earthing).

I've spent months and sleepless nights trying to get a product through the EMC certification. It's certainly possible but it's time consuming and expensive. With a shoestring engineering budget and a product that needs to be on the shelves in a month? Not really. I'm sure many devices on the market are not compliant. I follow lists of products removed from market for non-compliance and there are plenty each week. But…

[deleted]

Re: Transmit Radio Signals via Ethernet

#25

Post by derefr »

londons_explore wrote: post #21
4gotunameagain wrote: post #19

Earlier quoted context omitted.

This does not magically increase the power radiated by an ethernet cable or somehow change the base frequency of the interference. Furthermore, the power levels are very low. If you check the link at the bottom, he is using a directional (Moxon) antenna to receive this faint signal. If this could somehow pose an issue with anything, it would have been caught in EMI testing of all network equipment sold

EMI testing only tests a product during typical use. It's very possible to transmit illegal power levels with software mods, or even carefully crafted data packets in some cases.

> or even carefully crafted data packets

Unless you’ve made custom PHY hardware for those data packets to be pushed onto the line through, your data packets are going to be line-coded to ensure that the signal is self-clocking. Which basically precludes boosted harmonics.

Re: Transmit Radio Signals via Ethernet

#26

Post by norrius »

jcims wrote: post #15
skunkworker wrote: post #9

Earlier quoted context omitted.

I was thinking the same thing, have it exfil a secret key out of a server room (theoretically). I also got reminded about the method to send data from one computer to another over low frequency sound https://www.extremetech.com/computing/171949-new-type-of-aud...

Also through HDD noise https://arstechnica.com/information-technology/2016/08/new-a...

I love how a (metaphorically) air-gapped system can be attacked (literally) through the air. Maybe the truly critical things should also be vacuum-gapped (and put into Faraday cages while we're at it)?..

But the system still has some connection to the outside world, right? That means we could run some heavy GPU load and measure the variation in its power consumption, which apparently has been tried before: https://www.helpnetsecurity.com/2018/04/13/data-exfiltration...

Along these lines, the excess heat has to go somewhere, so maybe one could measure the variation in the work of the coolant system. I couldn't find any research about it right away (BitWhisper is similar, but a bit different), but I trust someone has already tried that.

Re: Transmit Radio Signals via Ethernet

#27

Post by jcims »

4gotunameagain wrote: post #19
coderjames wrote: post #10

Please don't try this at home! 118 MHz - 137 MHz is a protected Aviation band across the globe for airplanes to communicate with air traffic control. We already have enough industrial noise problems in this band; please don't contribute to pollution of protected spectrum. You will be interfering with the safe operation of the airspace. See: https://en.wikipedia.org/wiki/Airband

This does not magically increase the power radiated by an ethernet cable or somehow change the base frequency of the interference. Furthermore, the power levels are very low. If you check the link at the bottom, he is using a directional (Moxon) antenna to receive this faint signal. If this could somehow pose an issue with anything, it would have been caught in EMI testing of all network equipment sold

I think the issue is introducing a signal (particularly morse code) on a noise source that is typically steady state. I can pick it up pretty easily with just a bare UHF connector, no antenna.

Low risk overall but it's a good reminder.

Re: Transmit Radio Signals via Ethernet

#28

Post by vvanders »

4gotunameagain wrote: post #19
coderjames wrote: post #10

Please don't try this at home! 118 MHz - 137 MHz is a protected Aviation band across the globe for airplanes to communicate with air traffic control. We already have enough industrial noise problems in this band; please don't contribute to pollution of protected spectrum. You will be interfering with the safe operation of the airspace. See: https://en.wikipedia.org/wiki/Airband

This does not magically increase the power radiated by an ethernet cable or somehow change the base frequency of the interference. Furthermore, the power levels are very low. If you check the link at the bottom, he is using a directional (Moxon) antenna to receive this faint signal. If this could somehow pose an issue with anything, it would have been caught in EMI testing of all network equipment sold

Part 15 is pretty clear that any harmful interference should be minimized[1]. Even though it's low power that doesn't mean that it still can't be picked up. Just because equipment is sold at retail doesn't give you a free pass on it.

Take powerline ethernet where the power levels are "low" but still can cause significant issues[2].

[1] http://www.arrl.org/part-15-radio-frequency-devices#Myths

[2] http://www.elmac.co.uk/RF_Emissions_of_Powerline_Ethernet_ad...

Re: Transmit Radio Signals via Ethernet

#30

Post by avian »

4gotunameagain wrote: post #19
coderjames wrote: post #10

Please don't try this at home! 118 MHz - 137 MHz is a protected Aviation band across the globe for airplanes to communicate with air traffic control. We already have enough industrial noise problems in this band; please don't contribute to pollution of protected spectrum. You will be interfering with the safe operation of the airspace. See: https://en.wikipedia.org/wiki/Airband

This does not magically increase the power radiated by an ethernet cable or somehow change the base frequency of the interference. Furthermore, the power levels are very low. If you check the link at the bottom, he is using a directional (Moxon) antenna to receive this faint signal. If this could somehow pose an issue with anything, it would have been caught in EMI testing of all network equipment sold

As others have pointed out, EMC testing often only considers typical use and this is not one.

Another thing is that regulations don't only consider radiated power. Constant-level spurious transmissions are sometimes tolerated to a higher degree compared to modulated ones (e.g. in some bands maximum allowed interference is determined by quasy-peak level, not power). This is exactly because modulated interference (which is what this produces) is more harmful to communications systems.

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