Re: Advice for research project on detecting appliance use from radiated EMF noise #RTL #experiment #gnuradio #airspydiscovery

David Ranch

Hello Nathan,

Sounds like a very interesting research project and I imagine a LOT of people could learn from your findings!

One thought though: you mentioned this research was going to be "EMF noise that these devices email through the air" but I've always been curious if they are also radiating noise via the AC power lines as well.  Much like the electric or magnetic interference, this "conducted" interference on the AC lines could also help you find and detect things potentially even farther away.  I have to believe there can be a way to couple an SDR to the power line, cancel out the 50/60 cycle power, and view things in the frequency and/or time domains.

Anyway.. good luck with the research!


On 07/09/2020 11:01 AM, Nathan R wrote:
Hi all,

I am a graduate student currently exploring a new research project on activity recognition within a household setting by sensing when a user turns on or interacts with a particular appliance or electric device. The intent behind the project is to wirelessly detect device use by passively measuring the EMF noise that these devices emit through the air during regular use. Through past literature searches, we have identified the very low frequency range of 0-2 MHz as the target area where many of these devices are emitting noise. I did not have a lot of knowledge on antenna and radio design coming into this project, and only limited experience with SDRs, but have made some headway in the past few weeks. My setup thus far has consisted of using an RTL-SDR V.3 in direct sampling mode paired with a variety of pre-made antenna designs, of which I have achieved the best results with the MegaLoop 30+ MLA. I have also just ordered an Airspy HF+ Discovery and the Youloop antenna which I hope will help me to achieve even better SNR in the HF range.

From my readings and my background knowledge in electromagnetics, I have come to understand that these loop antennas perform better in the very low frequency ranges, but also couple to the magnetic component of radio waves. This appears to match with my experimental results where although I have been able to detect a variety of appliances and devices, such as TVs, washing machines, and light bulbs, it is only devices that generate strong magnetic fields, like power drills with DC motors, that I am able to detect from more than a foot away.

Especially once we get the new Airspy SDR, I am fairly confident in all of the areas of our pipeline except the antenna design. Thus my question is if there is anyone who, either purposely or accidentally, has had experience with detecting appliances from longer distances before, suggestions on how we could improve our antenna design for these lower frequencies, and thoughts on whether detecting these waves through the air at a house or room scale is even realistically possible at all.


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