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Logitech X-530 - AM radio frequency

  1. Oct 18, 2015 #1
    I have poorly made computer speakers - Logitech X-530. They sometimes pick up AM radio stations and pops up when lightning is turned off. What AM radio frequency is picked up by computer speakers? I am curious becaous some kinds of popping is picked up by computer speakers but it is not picked up by AM radio on frequency about 1600 kHz.
     
  2. jcsd
  3. Oct 18, 2015 #2

    davenn

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    hi there konrado5
    welcome to PF :smile:

    radio signals being picked up by audio gear is a problem as old as the 2 of them have been around.
    commonly caused by close proximity to a radio/TV station transmitter and the signal is easily overloading and being received by the audio gear

    Either the cable between your computer and the speakers and or the cable between amplifier and speaker acting as an antenna
    The signal is brought into the amplifier where is rectified/demodulated by the diode junction within any one of the transistors of the amplifier
    then amplified and outputted to the speaker(s) along with the computer sound

    RF chokes ( a few turns of the speaker cable(s) or input cable wound around a ferrite core along with some small value ceramic capacitors across
    the speaker lines and input line will often help ( capacitor values of around 0.01 - 0.1 uF could be experimented with)


    cheers
    Dave
     
  4. Oct 19, 2015 #3
    Perhaps I written this post not clearly enough but my question is merely question caused by curiosity. What AM frequecy is picked up if speakers acting as an antenna?
     
  5. Oct 19, 2015 #4

    davenn

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    you did and I answered :smile:

    since there is no specific tuned circuits in the cables/amplifier system, it will be prone to picking up the strongest signal there is nearby
    As I said, it may be a radio or a TV station .... It may even be a CB radio or a commercial VHF vehicle radio ... in say a taxi or a courier truck etc

    many years ago, when I lived in a different country, there was a PA system in a hall, I operated and looked after with several other colleagues
    We were regularly plagued with taxi cabs that would sit outside the building and use they radio to talk back to base and their audio would come
    blasting through the PA speakers. Those radios were on around 75 MHz and 10W transmit

    Other times I have seen gear from people that live within 5 - 10 km of a radio or TV broadcast transmitter and the RF signal can get into all sorts of electronics
    AM radio stations are typically around 10 kW transmit power and TV stations can be up around 100 kW. It can cause all sorts of weird problems

    maybe you have a station nearby ??


    cheers
    Dave
     
  6. Oct 21, 2015 #5

    Ouabache

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    In addition to what davenn has described..
    I too have experienced this phenomenon. At college when I wired speakers to the kitchen, my source signal (stereo receiver/turntable/CD player) was located in a distant room. When i played jazz or classical music through my speakers, during in the quiet sections I could hear a radio station. The long length of speaker wire across the apartment was probably acting as an antenna and coupled the signal into my wires and ultimately to my speakers.

    To find out what radio frequency it was. I took an AM/FM receiver and tuned across both bands until I found the station. It turned out to be our local college AM station WBAA on 920kHz. This is an example of what davenn described, the signal coming from a nearby AM station. The WBAA broadcast studio is on campus and the transmitter, over the ouabache river in the neighboring town. A digitally tunable AM receiver will show you what frequency is being picked up. Alternatively, if you listen; every broadcast station will identify with their call letters at least once per hour. If they don't happen to mention the broadcast frequency, you can look up their call letters on the web and quickly find out the frequency.
     
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