A car's engine rotates in the range of 500 RPM to 6000 RPM. This is in the audible range. The car's engine is activated using spark plugs which are an electrical system at the same frequency (or some harmonic).

Turning on the radio to an AM receiver, you can sometimes hear a sound at the frequency that the engine is spinning. I believe this happens because the electrical system radiates EM with a broad spectrum and it is enveloped at the audible RPM rate. The broad spectrum intersects with the receiver frequency selection.

Is there a name for this type of system?

Are there any effective DSP techniques for selecting and "receiving" the RPM sound in this scenario?

My application is a transmission scheme similar to the above. My receiver will be a software defined radio.

  • $\begingroup$ Sure: it's name is "interference." But since you want to capture the spark plug bursts, you want an AM radio without any squelch control, or better yet just a big antenna loop connected to a low-pass filter. What is your goal? There are simpler ways to count the firing rate or check for misfires, etc. $\endgroup$ – Carl Witthoft Mar 1 '16 at 12:32
  • $\begingroup$ Have published the real project to github.com/fulldecent/system-bus-radio Way more fun than getting the firing rate! $\endgroup$ – William Entriken Mar 5 '16 at 16:18

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