Reddit and GitHub user iminehard noticed their cellphone experienced interference while near their impressive GPU mining farm. Following this, iminehard investigated the issue and found that there was a definite increase in noise around a specific LTE range. iminehard’s testing methodology and results are covered in more detail below.
“TL;DR – Large number of GPUs in open air crypto currency mining “rigs” emit substantial spurious emissions/noise on portions of the LTE spectrum used in the United States.”-GitHub and Reddit user iminehard
Testing for interference
iminehard documented their testing methodology along with their results. Testing made use of a Laptop, an RTL-SDL tuner, and an omnidirectional antenna for said tuner. SDL, or Software Defined Radio, allows you to use a computer to capture and produce RF signals, using its CPU to process the signals. This is different from regular radio, which uses specialized hardware to process the signal. Iminehard used this to capture the frequencies on which LTE operates.
The first pair of tests iminehard performed was a single GPU inside a case, first at idle, but overclocked and with fans on, and the second with the mining software bminer running. No perceptible difference can be seen on the charts comparing the LTE spectrum between the two tests. The lack of difference between the charts could mean a few things. Namely, it could mean that the case used blocked or grounded out the interference. Otherwise, it could mean that the interference generated by a single GPU is undetectably negligible.
Moving forward, iminehard tested their mining farm, with interesting results:
iminehard used the same testing method that was used above on their farm. And unlike the previous test, there was a significant change in what iminehard called “range 1” of the LTE spectrum used by the United States (617-746 MHz).
Results of interference
As shown above, there is some definite interference caused by large-scale GPU farms. This interference may cause service disruptions for those trying to use cell phones within the field. Due to the fact that this may cause service interruption, the farms may break federal laws regarding intentional interference. Or may cause the FCC to come knocking on your door asking you to knock it off.
Shielding to prevent interference
The above tests were performed on ‘open’ GPUs. ‘Open’ referring to the fact that the GPUs were not mounted in a metal case. A metal case may provide some shielding for the interference that the GPUs release, either due to grounding or construction. Aside from being sure to mount all GPUs in a real case, one could build a Faraday cage around the entire farm. A correctly built faraday cage should contain all the interference within the cage. One major downside to using a Faraday cage is that Faraday cages are conductive. If it collapses, it could damage equipment.