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

Post by Doxin » Thu, Jan 18, 2018, 9:50 AM UTC

DanBC wrote: post #70

cestith wrote: post #35

Back a couple of decades, my alphabetic pager was going off but the messages were gibberish. It turned out the CPU in the PC I'd been asked to look at was a Pentium running at 150 MHz. I'd set my pager directly on top of the case, and the nominal frequency for it was 150.5 MHz, frequency modulated. The lines in the motherboard can be used as antennae and the CPU pins can produce a clock pulse and modulate it. There u…

> There used to be a parallel port audio device for PCs which was mainly just different resistors. The driver for it just timed pulses to the different pins. Resistor ladder DA converters are pretty fun. https://en.wikipedia.org/wiki/Covox_Speech_Thing https://hackaday.com/2015/11/05/logic-noise-digital-to-analo... https://www.tek.com/blog/tutorial-digital-analog-conversion-...

Post by anfractuosity » Thu, Jan 18, 2018, 2:40 PM UTC

randyrand wrote: post #108

lovelearning wrote: post #36

Earlier quoted context omitted.

Here's one. This sentence from the linked paper is informative - "When data is exchanged between the CPU and the RAM, radio waves are emitted from the bus's long parallel circuits." For some background: Digital circuits like computer motherboards have components called oscillators that switch voltage on and off a number of times every second. This is what "clock speeds" refers to - 2.8 GHz CPU clock speed means volta…

First realize the aptitude modulation in this radio is very crude. Unlike normal radio which has many amplitudes, this radio only has 2. On and off. Tone or no tone. This radio has no control over the exact amplitude. Due to this limitation, this radio can only transfer a single tone at a time. Music must be monophonic. To transfer a 60htz tone we just switch between the on and off state at 60htz. The On state will b…

Post by randyrand » Thu, Jan 18, 2018, 7:04 PM UTC

anfractuosity wrote: post #123

randyrand wrote: post #108

Earlier quoted context omitted.

First realize the aptitude modulation in this radio is very crude. Unlike normal radio which has many amplitudes, this radio only has 2. On and off. Tone or no tone. This radio has no control over the exact amplitude. Due to this limitation, this radio can only transfer a single tone at a time. Music must be monophonic. To transfer a 60htz tone we just switch between the on and off state at 60htz. The On state will b…

Despite the fact you can only modulate the carrier on/off, you can still also output normal music with speech etc using pulse density modulation - https://news.ycombinator.com/item?id=16168317 Which I don't think is monophonic, but I could be wrong?