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I Physics of noise picked up by a radio when home lights are switched off

  1. Mar 22, 2016 #1
    I would like to get an, if possible, detailed analysis of the phenomenon by which you hear a noise in your radio speakers when the home lights are switched off. It probably has to do with a wave packet emitted due to switching off the lights, which is picked up by the antenna of a conventional radio appliance. I would like to have a reference with a detailed analysis how this wave packet is generated and at what frequency bandwidth it is emitted.
  2. jcsd
  3. Mar 22, 2016 #2


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    The very first radio transmitter was a "spark" transmitter. So if there is a spark somewhere in the system (fluorescent lights), it will generate a broadband noise.
  4. Mar 22, 2016 #3


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    The answer to this question really does depend on your existing state of knowledge.
    Any circuit consists of Resistive, Inductive and Capacitative elements, not necessarily by design but because if its dimensions and shape. When a switch is opened, the Inductance will cause an induced voltage spike. That's a consequence of Lenz's Law and the spike will be of a polarity to resist the drop in current and cause a spark (greater or less depending on the details) and the current will gradually die down in a series of subsequent spikes. These current spikes can have a spectrum that can covers lf, mf, hf and vhf bands. This energy will radiate from the structure or appliance to cause interference in the form of EM waves. The EM wave is radiated by exactly the same mechanism that a normal Radio wave is radiated from a transmitter and antenna. (Radio Frequency currents will cause RF radiation from anything.
    I suggest you start reading around the subject, which is very wide and covers a range of knowledge start level. This wiki link could get you started. Otherwise, you could do a google search based on 'elementary antenna theory' or some such terms.
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