signal and bandwidth

Discussion in 'Wireless & RF Design' started by aac9876, Dec 23, 2007.

  1. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    How can I have a poor wifi signal -82 and a still have a pretty good speed on download and upload. Can someone
    explain why bandwidth can make up for this..??
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
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  3. nanovate

    Distinguished Member

    May 7, 2007
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    Your wifi receiver might pretty sensitive. Many are better than -82dB at 11Mbps.

    You need to quantify "pretty good speed" ... signal strength is only part of the equation. You can have a very strong signal but have very poor data throughput. For instance if you are in a location that has lot of other wireless devices.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    There should be also written where is the noise. If the signal is like 8db higher than the noise, then it usually has usable data flow for good bandwidth.
     
  5. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    its -82 dbm that sucks for a signal . usually with this external antenna,Yagi<at that dbm, i get terrible service. that time it was good. Usually good means -60 or better dbm. Here is the way I understand this...
    The signal has microscopic modulations on the sine wave.
    Those wave lay over a chip for a fraction of a second and if
    a little jog in the wave hits a semiconductor it produces micro current and is a 1. otherwise its a 0. Right??
    the chip has conductors that are exactly the right size for a 2.4- 2.45 gighz wave.. right???
    So how does bandwidth work with this in mind..??
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Everything's relative ;)

    You might have a -20dB signal, but +20dB of noise on top of it, and you won't be getting much data across.

    Are you anywhere near a cellular tower, airport, or radio station? Sideband emissions from such sources can swamp low signals, even from many gigahertz away. Even just a cellular telephone in a weak reception area could swamp your 2.4GHz signal, since they use the same band; the tower would tell the cell phone to boost it's signal to compensate for the low signal, generating lots of noise.

    Recently in a city in Colorado, residents have found their garage doors opening and closing at random intervals. It turns out that the US Air Force recently installed a high powered transmitter for emergency communications, and one of the sideband harmonic frequencies just happens to be on the same frequency as many garage door openers. :rolleyes: The fix for that would be for the USAF to install a passband filter in their antenna - but they may object to the loss in sensitivity.

    You could try using a more directional antenna. Yes, a Yagi is certainly highly directional ... but you might consider adding a corner reflector to it.

    If your antenna is made of aluminum, inspect it carefully for corrosion. Where I live it's quite humid, and raw aluminum left outside corrodes rather rapidly. This will wreak havoc with your selectivity/sensitivity.

    After you've given it a thorough cleaning up, I suggest treating it with a product called "CorrosionX" - you can search for it online. It's used by the U.S. military to preserve aircraft that are used in corrosive environments. It's not particularly cheap, but it works really well.
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    One problem I've ran across was the use of wireless broadband routers and cordless telephones. The two can intefere with one another ... and it's best to keep them on different channels.

    In the cases I've seen, you had very good signal and terrible performance ... if any.

    When your in an apartment complex, it can get interesting. :D
     
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