jamming a signal ?

Discussion in 'Wireless & RF Design' started by Mathematics!, Mar 24, 2012.

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  1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    I know jamming an FM , AM or any non Spread Spectrum based signal is not that hard as long as you are able to create deconstruction interference to cancel the wave out. (just math get the wave to be y=0 on the graph.)
    And I also know devices exist for doing that

    But when it comes to Spread Spectrum based signal / frequency hopping signals based on a PN code. I have read that these are hard to jam.

    But in theory if you where to create deconstruction interference on all the channels hopped I would think you could in theory jam these signals to.
    So I can see Spread Spectrum providing security from making since of intelligent data. (only people that could make since of the data is the people that knew the pn code ) But I don't see it totally immune from jamming.

    I post here because somebody I was talking to believes that
    Spread Spectrum is immune from jamming. I agree with him on the security of data being almost impossible to make sense of without the pn code but I disagree with him in saying that they are still jammable.

    But maybe I am wrong about the jamming of the signal.

    In theory if you where able to make all the waves in consideration y=0 then it would be totally jammable. But I don't know how practical or weather we have the capabilities to create a device yet that can jam all the hopped signals/all signals in a spectrum.

     
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    The former USSR had jamming devices that could completely overload the receivers in the HF to VHF spectrum for huge areas. There were times when we didn't even try and used semaphore for communications between ships before satcomm was common.

    It's not really a jammer but this thing drove me crazy back then when I ran military long-range HF networks. http://en.wikipedia.org/wiki/Russian_Woodpecker
     
  3. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    Ok, I know in theory Spread Spectrum can be jammed completely.
    But in practices do the government or agency have the ability to put the math on paper to physical device. Meaning can they create it to completely jam a spread spectrum signal like in wifi or 3g ...etc etc

    I know creating the actual device could be harder then doing the simple theory out obviously
     
  4. Blofeld

    Active Member

    Feb 21, 2010
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    I don't think that destructive interference is how jammers operate. My understanding is, that you just try to "swamp" the frequency range that you want to jam with noise.
     
  5. nsaspook

    AAC Fanatic!

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    Lets just say a "government or agency" with a almost unlimited budget can build anything within the known laws of physics and engineering.;)
     
  6. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    Well you right that would normally be the easiest way.

    But in theory you could do it by destructive interference as well. In theory


    Great to know this so if I work out some theory using quantum entanglement to travel back in time. They will have the stuff to build it. :)
     
  7. nsaspook

    AAC Fanatic!

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    You're too late. One of the chief scientists designed one in the 1960s.

    http://www.youtube.com/watch?v=3MByhY6aSUo&feature=related
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Why the sudden interest in jammers? You are bumping up against the TOS with this one. When you jam a signal, you are destroying a legitimate business, and are in violation of law. In the case of phone jammers, it is a direct violation of ToS, because it is a safety violation.

    Unless you are at the source, destructive interference is not possible, there will be nulls and peaks of the RF wave. So you would be forced to have a powerful transmitter

    Since this thread is both illegal and immoral I am closing it. If you wish to pursue this subject do it elsewhere.
     
    Last edited: Mar 26, 2012
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