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Strange Radio Reception

  1. Jul 26, 2009 #1
    Right this is a question about some radio noise that I picked up from my speakers last night.

    My speakers were plugged into my tv with the volume off, this tv was plugged into a Freeview box which had an aerial cable plugged into that connects to the aerial in the loft.

    Just after I plugged in the speakers I heard some sounds coming from them even though the volume was set to 0 and the tv was turned off. I put the speakers to my ears and I heard radio stations that seemed to be fading in and out (increasing and decreasing in volume) and there must of been more than 5 (maybe loads more) and some were speaking in french and russian and no one radio station was clearly audible for more than about 3 seconds, even whilst you could hear one you could hear another in the background, this would then fade out and another would fade in.

    When I removed the aerial cable the radio reception would stop so I think the aerial in the loft must of been picking up the radio stations, a strange thing is that I tried the same setup this morning and I couldn't pick up any radio stations, also I swear I could hear really old and odd music that was pretty spooky at the time (like out of a movie), sung in french so is it possible to pick up old radio signals or do they fade away?

    Also how could I have picked up this signals in the first place?
    Could the weather have been the cause? (it was slightly stormy last night, low pressure)
    Why did I pick up loads of different radio stations?
    Why did they keep fading in and out?
     
  2. jcsd
  3. Jul 26, 2009 #2

    Born2bwire

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    Reception is usually better at night. I forget the exact reasons but long range radio signals propagate by bouncing off the ionosphere. The ionosphere is a plasma and is dispersive. One of the consequences of a dispersive medium is that the reciprocity theorem is not guaranteed, that is, if you receive a radio signal off of the ionosphere, you may not be able to send your own signal back to the original transmitter. Things can get a bit tricky when it comes to trying to bounce the signal, any ham radio operators might be able to give much more detail on this.
     
  4. Jul 26, 2009 #3

    DrGreg

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    Welcome to the forums, Chris28!

    As you used the word "Freeview", I assume you are from the UK, like me. For the benefit of other readers, "Freeview" is the name of the UK's terrestial broadcast digital television system, in the UHF band 474-850 MHz.

    As Born2bwire said, at night and under abnormal weather conditions, radio signals can travel further than usual, so radio signals from France, Germany, Russia, etc can sometimes reach the UK. On top of that, aerials and electronic equipment can sometimes do what they weren't designed to do and pick up strong radio signals (at very low volume), even when switched off! Whatever you heard was a live broadcast, radio signals certainly don't hang around for years after transmission! (I'm not sure if this is possible, but they possibly even might be analogue television transmissions rather than radio stations.)

    The fading would be due to changing atmospheric conditions and the fact that several stations may have been transmitting on the same frequency and interfering with each other.
     
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