WiFi Cabling - dB loss per foot

Discussion in 'Wireless Internet' started by Dennis, Oct 9, 2008.

  1. Dennis

    Dennis Guest

    The antenna on my network card needs to be sitting in my window to
    access a public AP. This is very inconvenient. I was thinking about
    getting an extending cable for my antenna, about 15 feet long, but
    from what I understand there is extreme signal loss per foot when
    dealing with WiFi cables. I forget the math but it's around 5dB of
    loss for 15 feet, which is pointless if your going to use a 5dB

    So I'm thinking of using something like this, as it uses a USB cable
    to cover the distance:

    My question(s) are: Will I experience the same extreme dB loss using
    this on a 15 foot USB cable instead of a 15 foot WiFi cable with an
    antenna at the end? Is the USB signal amplified somehow? How do people
    who put antennas on their roof and connect them to a computer in their
    basement deal with signal loss on the 20-30 foot cable? etc etc

    (other solutions/links are welcomed)

    Thanks in Advance Guys
    Dennis, Oct 9, 2008
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  2. Dennis

    miso Guest

    There is no RF loss with USB. You might want to consider a moderate
    gain directional antenna of you are going to put this by the window.

    I think the general consensus is high power doesn't buy you all that
    much unless you have high power on both sides (host and client). So
    you don't need this particular unit. The newegg review complaining
    about mobo problems may have a usb power issue, especially in the case
    where it connects then drops.
    miso, Oct 9, 2008
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  3. Dennis

    seaweedsl Guest

    USB is one good way to go. Another USB adapter to consider at

    Removable antenna is smart. That way you can always upgrade if you
    need a better connection.

    Also, you might consider an ethernet bridge adapter. These will
    connect to your computer using ethernet cable, which has a theoretical
    limit of 100 meters! Zero loss.

    Here's a cheap one: http://www.newegg.com/Product/Product.aspx?Item=N82E16817201523

    It's called AP, but does more- under features:
    "Provides station mode to act as a wireless LAN client station"
    seaweedsl, Oct 10, 2008
  4. Dennis

    DTC Guest

    You might want to look at the Ubiquiti Nanostation 2 for $79.

    DTC, Oct 10, 2008
  5. Dennis

    miso Guest

    Not a bad idea, though it require a wall wart, while the USB device is
    powered via the cable. My experience is USB is more likely to have a
    driver problem than ethernet. I think any ethernet device other than a
    card on the bus doesn't need a driver.
    miso, Oct 11, 2008
  6. Dennis

    Dennis Guest

    Great info thanks guys!

    The Nanostation looks very interesting, I'm tempted... but it uses
    power over ethernet so I'll need a PoE network card or adapter? Is
    this it? http://www.newegg.com/Product/Product.aspx?Item=N82E16833127059

    Also I'm a bit confused about what makes it a good antenna. The main
    number I've been focused on is the tx/rx dB, the webpage says the
    Nanostation says it's "10dB x 2"? In reality what's that mean? 20 dB?
    I've been looking at some of the homemade antennas on YouTube... some
    claim to be around 12dB etc etc ... how does a commercial antenna like
    this compare; what other numbers factor into it?
    Dennis, Oct 11, 2008
  7. You are on the right track using a USB wireless adapter and usb
    extensions (if necessary) to your computer. Low loss coaxial cable is
    expensive, and still loses too much of the signal to be worth the
    trouble. There are a couple of higher power (500 mw) wireless
    adapters on the market, but you should do fine with a good USB device
    in the window, running a cable to one of the ports on your computer.
    Consider using a powered hub if you need to run more than 2 meters of
    USB cable. It works! You can use an adapter in a top-floor window
    and pass USB data to your basement this way...

    Take a look at the wi-fi antennas page: http://www.ab9il.net/wlan-projects/wifi1.html
    for some home-build ideas. A bit of gain can greatly extend your
    range / data rate.

    Good Luck

    ab9il.worldwide, Oct 11, 2008
  8. Dennis

    F8BOE Guest

    An AP in client mode would do it if there is an AC plug nearby.
    Most APs can be run in several modes and only need a CAT 5 or 6 cable and
    are OS independent.

    D-Link's DWL-G730AP is a good example...
    F8BOE, Oct 11, 2008
  9. Dennis

    seaweedsl Guest

    Couple more comments to help clarify your options:

    USB: If you have USB 2.0, then you should not need a USB hub until
    you are over 15 feet. So, USB should work well buying nothing more
    than the USB adapter and a 15' extension. This has been my experience
    with a couple different USB adapters.

    Ethernet: What DTC is saying is that you will not need anything extra
    with the Nanostation to use it. If I understand correctly (have not
    used it) the Nano comes with an injector that you plug the ethernet
    cable into and then it adds power for the nano for the cable that
    comes out of it. So you will need two ethernet cables; laptop to
    injector, then injector to Nanostation. (DTC; please correct me if
    I'm wrong, guys)

    For the cheaper AP/client adapters, you will have to plug in it's wall
    wart power supply directly to the back of the adapter. From what I
    can tell, this is not an issue if it is to be used indoors on your
    windowsill. POE seems to make sense for installations that are
    outdoors or more than 10-20 feet from a wall plug perhaps.

    Antennas. If you are getting acceptable connections at the window
    with your adapter card and antenna, then whatever antenna that comes
    stock with your adapter should be fine. I really doubt that you need
    even a 10dbi antenna, not to mention something more powerful. Probably
    a simple 2 dbi omni antenna (could add a reflector) is fine,
    considering what you have reported so far.

    What is the gain on your current working setup's antenna? Is it a
    adecuate connection when at the window ?

    Cables: There are antenna cables that are lower loss. The LMR400
    cable (about 1/2" thick) loses .25 db per meter at 2.4 Ghz. So a 3
    meter cable would lose .75 db. Call it 1 db with connector loss. But
    these are thick and expensive and will require pigtail adapters to be
    flexible enough to use. Do-able, but not practical.

    seaweedsl, Oct 12, 2008
  10. Dennis

    DTC Guest

    That's correct...you need two cables. The NS is auto-sensing, so it can
    be a crossover or straight cable. If your hub or switch has 49 volt PoE,
    it won;t pass through the NS's power injector. You just can't plug the
    NS directly into the 48 volt hub.
    DTC, Oct 13, 2008
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