Build Your Own EMI Probes

[Gerald Musy] wanted to investigate the source of electromagnetic interference (EMI) in his switching power supply design. Stymied by the high cost of EMI probes, he decided to build his own. Lucky for us, he wrote up his results of experimenting with four different designs.

The probes include an unshielded loop, a shielded loop, a ferrite core probe, and an electric field probe. None of these are especially complex to build–the ferrite core one is probably the most involved–you can see from the scope traces that the different probes pick up different information.

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Listening to Electromagnetic Interference with a RTLSDR Dongle

Being curious by nature, [Marios] decided to see what kind of radio-frequency emissions may be generated by an Arduino connected to a simple breadboard wire, and more importantly try to pick them up using a RTLSDR dongle. Electromagnetic interferences are disturbances that affect electrical circuits due to either electromagnetic induction or electromagnetic radiation. Before going into the market, all electrical devices are thoroughly checked for unwanted electromagnetic emissions so they usually aren’t obvious suspects when such problems arise.

Using the Arduino embedded PWM controller in fast PWM mode and by manipulating the duty cycle, he actually managed to create a primitive form of amplitude modulation and was able to transfer a very simple audible signal at several frequencies up to 1.75GHz. Embedded after the break here is video of the system at work.

As a side note, did you know that during the solar storm of 1859 the EMI were so strong that the telegraph operators received several shocks? Pipelines maintenance systems also have to be aware of such events, that can lead sensors to provide inaccurate results.

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