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Thread: Unknown activity - industrial activity near airport

  1. #1

    Default Unknown activity - industrial activity near airport

    Hi all

    Anyone got any idea what this is? Its taken from a heavy industrial location which is next to a busy international airport.
    This pattern is seen across all of the site (all the bits I've looked at so far.)
    The pattern seems to be extremely regular, although possibly the spacing changes from time to time (unsure as havent had time to examine it all yet.)

    Seems to be roughly:
    - Every 3 seconds, a 1 second pulse around 10-15Mhz wide, ranging all across the 2.4Ghz spectrum
    - Every 45 seconds or so, a 5-7 second pulse across the entire spectrum

    These results are consistent across a very large area and dont seem to be tied to any particular machinery or potential interferer.

    There is some strength to these signals, so I'm keen to understand what it is.
    There is no wireless ethernet deployed at the site. There are a few 802.15.4 transmitters, although they dont produce anything like this, obviously.

    Any thoughts gratefully received!

    Click image for larger version. 

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  2. #2



    I am wondering if the Every 3 seconds, a 1 second pulse symptom is your Wireless card. If you disable your wireless card in the Device manager do they go away? Not sure about Every 45 second, across the full spectrum. Is there any Security equipment at the site like a video camera that may be transmitting every 45 seconds?

    Also, can you send a 5 - 10 minute recording to And put my name on it?


    Last edited by Richp01; 05-17-2011 at 08:39 AM.

  3. #3


    Did a little investigation into Radar and there is a L-Band radar that is used for Air Traffic Management that runs in the 1 - 2 GHz Frequency range. So it may be the cause of the 45 second interference.

  4. #4


    Can you please upload a recording in the forum to look at.. the image is a little blurry.. Thanks..

  5. #5

    Default 5 Minute capture

    Thanks for the responses, capture attached.
    Note, from this location 3 APs from a distant, neighboring installation 802.11 network can be seen at very low signal strength, although there appears to be no traffic on them and a such they dont obscure the strange signal I'm seeing.

    I'm now thinking that actual the two patterns are separate things, but don't know that for sure. Suspicion is that the the wideband 5s burst every 45s or so is pure noise from something industrial. The 3s pulses though, really look like something deliberate.
    However I have no evidence to support this!

    FYI, not only is there an airport to the North, there is also a major port around 1.5 miles to the South East (wasn't clear to me yesterday as I hadn't been to that part of the site.) Something maritime maybe??

    Unknown - 5 mins.wsx

  6. #6


    Further info:
    - Havent tried disabling local wireless card and taking a capture, will do so tomorrow. BUT...same results seen on two machines, and captures taken 5 miles from the site (where my hotel is) do not show the same patterns (they are normal looking captures.) I will try this though tomorrow.
    - There are security cameras, but they are all fibre connected as far as anyone can tell. Also, the wideband pulse seen every 45s is across a very large area (like, 50-100 acres or more) of medium to high-density industrial plant. I cant see any wireless cams pushing out that much power. Also, there aren;t that many of them in the heart of the plant, they are only round the edges, so physically pretty distant.

  7. #7


    I believe I've cracked it.
    The short pulses are S-Band ground location radar from the airport.
    The wideband noise, I've homed in from 30 odd captures to one specific area in the plant (thanks Chanalyzer for making that easy) and there is a very large compressor mounted some 6m above ground - which explains the wide area that the noise is seen in.

  8. #8


    Glad to see that you have found what appears to be the cause of the spectrum interference.

  9. #9


    Hi Trubloff,

    I believe you have. I have been working with 2.4GHz since 1996 before it was an open system and I have had problems with ground radar in warehouses next to two international airports in that time. In one location it worked in our favour as a competitors kit was FH and could not cope with the interference whereas we could change our operating frequency on our direct sequence kit to avoid it.


    Phil B


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