# Using HDMI EMI for fast wireless data transfer

DevFeed: [Using HDMI EMI for fast wireless data transfer](<https://devfeed.tech/articles/using-hdmi-emi-for-fast-wireless-data-transfer-21659.md>)

Original publisher: [Read original article](<https://www.windytan.com/2023/02/using-hdmi-radio-interference-for-high.html>)

Author: Oona Räisänen (noreply@blogger.com)

Published: 2023-02-27T21:02:00Z

Content type: tutorial

Language: en

Sources: [Oona Räisänen](<https://devfeed.tech/sources/oona-raisanen.md>)

Topics: [hdmi](<https://devfeed.tech/topics/hdmi.md>), [monitor](<https://devfeed.tech/topics/monitor.md>), [vulnerability](<https://devfeed.tech/topics/vulnerability.md>), [Raspberry Pi](<https://devfeed.tech/topics/raspberry-pi.md>), [data](<https://devfeed.tech/topics/data.md>)

Tags: [communications](<https://devfeed.tech/tags/communications.md>), [hdmi](<https://devfeed.tech/tags/hdmi.md>), [monitor](<https://devfeed.tech/tags/monitor.md>), [raspberry-pi](<https://devfeed.tech/tags/raspberry-pi.md>), [security](<https://devfeed.tech/tags/security.md>), [side-channels](<https://devfeed.tech/tags/side-channels.md>), [tempest](<https://devfeed.tech/tags/tempest.md>), [vulnerability](<https://devfeed.tech/tags/vulnerability.md>), [webcam](<https://devfeed.tech/tags/webcam.md>)

## AI overview

The article investigates wide-band radio interference from a monitor and shows how HDMI electromagnetic emissions can reveal a distorted image of a Raspberry Pi desktop. It connects the observation to the known monitor-eavesdropping technique called van Eck phreaking and explores whether the emissions can transfer additional information.

## Source excerpt

This story, too, begins with noise. I was browsing the radio waves with a software radio, looking for mysteries to accompany my ginger tea. I had started to notice a wide-band spiky signal on a number of frequencies that only seemed to appear indoors. Some sort of interference from electronic devices, probably. Spoiler alert, it eventually led me to broadcast a webcam picture over the radio waves... but how? It sounds like video The mystery deepened when I listened to how this interference sounded like as an AM signal. It reminded me of a time I mistakenly plugged our home stereo system to the Nintendo console's video output and heard a very similar buzz. Am I possibly listening to video? Why would there be analog video transmitting on any frequency, let alone inside my home? If we plot the signal's amplitude against time we can see that there is a strong pulse exactly 60 times per second. This could be the vertical synchronisation signal of 60 Hz video. A shorter pulse (pictured above) can be seen repeating more frequently; it could be the horizontal one. Between these pulses there is what appears to be noise. Maybe, if we use the strong pulses for synchronisation and plot the amplitude of that noise as a two-dimensional picture, we could see something? And sure enough, when main screen turn on, we get signal: (I've hidden the bright synchronisation signal from this picture.) It seems to be my Raspberry Pi's desktop with weirdly distorted greyscale colours! Somehow, some part of the monitor setup is radiating it quite loudly into the aether. The frequency I'm listening to is a multiple of the monitor's pixel clock frequency. As it turns out, this vulnerability of some monitors has been known for a long time. In 1985, van Eck demonstrated how CRT monitors can be spied on from a distance[1]; and in 2004, Markus Kuhn showed that the same still works on flat-screen monitors[2]. The image is heavily distorted, but some shapes and even bigger text can be recognisable. So