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System Bus Radio: Transmits AM radio on computers without transmitting hardware

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Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#21

Post by kabdib »

I debugged a boot issue on the Apple Newton this way. The latest flash image was a brick on production hardware (no available LEDs, GPIOs, etc.) but not on development hardware. But I could flash a new OS image.

So I wrote some small loops that did different stuff on the bus (so that they sounded different) and salted the boot path with them, then listened in on my portable AM radio. Found the problem inside of an hour by moving the loops further down the path.

There were probably other ways to do this (could have coaxed a hardware tech in the lab to solder in a GPIO), but this way was more fun. :-)

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#22

Post by BuildTheRobots »

There's also PiFM[1] which (iirc) modulates one of the GPIO pins fast enough on a Pi to produce an FM radio signal.

It's fun to play with, and is a great hack, but please don't try and use it for anything or any length of time; it puts out a tonne of horrible harmonics all over the radio spectrum.

[1] https://github.com/rm-hull/pifm

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#23

Post by luk32 »

godelmachine wrote: post #19
zenkat wrote: post #13

Earlier quoted context omitted.

What part of the computer is emitting the radiation? And how is this program manipulating it to generate a song?

The CPU colloquially called the processor does this. When you feed a program to the CPU, it switches between logic gates (read - transistors turning on and off), to process the program. As the processing elements switch between power levels of 0 and 1 (0V & 5V / 0V & 12 V), there are electromagnetic fluctuations. These EM fluctuations are the emmissions we are talking about here.

I highly doubt that cpu is the emitter. More probable is some long path on mother board, used for data communication.

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#24

Post by ComputerGuru »

godelmachine wrote: post #19
zenkat wrote: post #13

Earlier quoted context omitted.

What part of the computer is emitting the radiation? And how is this program manipulating it to generate a song?

The CPU colloquially called the processor does this. When you feed a program to the CPU, it switches between logic gates (read - transistors turning on and off), to process the program. As the processing elements switch between power levels of 0 and 1 (0V & 5V / 0V & 12 V), there are electromagnetic fluctuations. These EM fluctuations are the emmissions we are talking about here.

I don’t think the FETs generate enough EM on their own? It’s probably the inductors on the motherboard charging and discharging as a result of the FETs that cause the EM whine/hum?

Another likely source is the power supply, which has coils by the dozens and will react to varying loads of computational work. The cheap ones are already all over the radio spectrum even when you don’t want them to be.

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#25

Post by ComputerGuru »

baq wrote: post #20

side channel information leak for two, please

Definitely. Here’s a decent paper: https://www.cs.jhu.edu/~astubble/600.412/s-c-papers/em.pdf

I know there’s a story about US and Russian intelligence using this at an embassy or something, but I can’t find it.

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#26

Post by godelmachine »

ComputerGuru wrote: post #24
godelmachine wrote: post #19

Earlier quoted context omitted.

The CPU colloquially called the processor does this. When you feed a program to the CPU, it switches between logic gates (read - transistors turning on and off), to process the program. As the processing elements switch between power levels of 0 and 1 (0V & 5V / 0V & 12 V), there are electromagnetic fluctuations. These EM fluctuations are the emmissions we are talking about here.

I don’t think the FETs generate enough EM on their own? It’s probably the inductors on the motherboard charging and discharging as a result of the FETs that cause the EM whine/hum? Another likely source is the power supply, which has coils by the dozens and will react to varying loads of computational work. The cheap ones are already all over the radio spectrum even when you don’t want them to be.

The transistors also have a drain and a source :)

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#27

Post by godelmachine »

luk32 wrote: post #23
godelmachine wrote: post #19

Earlier quoted context omitted.

The CPU colloquially called the processor does this. When you feed a program to the CPU, it switches between logic gates (read - transistors turning on and off), to process the program. As the processing elements switch between power levels of 0 and 1 (0V & 5V / 0V & 12 V), there are electromagnetic fluctuations. These EM fluctuations are the emmissions we are talking about here.

I highly doubt that cpu is the emitter. More probable is some long path on mother board, used for data communication.

The CPU is comprised of millions / billions of transistors which switch on and off multiple times (which depends on the base clock frequency).

Re: System Bus Radio: Transmits AM radio on computers without transmitting hardware

#30

Post by lovelearning »

luk32 wrote: post #23
godelmachine wrote: post #19

Earlier quoted context omitted.

The CPU colloquially called the processor does this. When you feed a program to the CPU, it switches between logic gates (read - transistors turning on and off), to process the program. As the processing elements switch between power levels of 0 and 1 (0V & 5V / 0V & 12 V), there are electromagnetic fluctuations. These EM fluctuations are the emmissions we are talking about here.

I highly doubt that cpu is the emitter. More probable is some long path on mother board, used for data communication.

Yes, it's the bus traces between CPU and RAM. From linked paper: "When data is exchanged between the CPU and the RAM, radio waves are emitted from the bus's long parallel circuits."
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