PC fan produces 200 Hz EM field synchronized to mains frequency

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Ravaner
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Hello. I need an explanation for a strange phenomenon ... I use a fan (PC type) powered by mains (220 V / 50 Hz in my country). At a distance of about 3', I get a sin EM field (sure it is not by mains cords) at a stable frequency of 200 Hz synchronized on main frequency. Even during power on (acceleration) and power off. During these periods amplitude grows or decreases but frequency is sill 200 Hz. If someone can explain that, thanks by advance ...
 
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I wonder if the motor has 4 poles? Maybe that would account for the 200 Hz "back feeding" on the mains.
 
Curious. 200 Hz, being an even order harmonic would require some sort of asymmetric distortion. If the stator of the motor simply went into partial saturation on both +/- halves of the current peak, this wouldn't happen. Rectification would cause it...
Is there a permenant manget nearby?