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Wi-Fi antenna

Discussion in 'Boat Electronics' started by Bruce, Apr 10, 2010.

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  1. Bruce

    Bruce Guest

    A new one.

    I'm now residing ashore as I sold my sailboat. The place I rented is
    nearly a mile for the marina and I can sometimes log onto the marina's
    free Wi-Fi net using the laptop's built in antenna.. I am using a
    Wi-Fi transceiver that has some level of amplification, or at least it
    is sold as a "high powered" Wi-Fi.

    I have built a parabolic antenna which (according to the rather crude
    signal strength meters included with Linux) seems to approximately
    doubles the signal strength and allows me to access two additional, of
    the five or six different circuits at the Marina.

    Question: I am now building a larger parabolic antenna system. The
    original was a ten inch dish and the new one will be a 17 inch dish.
    Are there any formula to estimate the additional gain of the 17 " over
    the 10"? In addition the first effort was screen and the second will
    be solid aluminum. Again any estimates of gain increase - decrease .

    I realize that there are many slip between the cup and the lip and
    nothing is certain about antenna systems so am looking for estimates,
    best guesses, text book "rule of thumb" basically any information
    about parabola size or material and gain.

    I do have the basic formula to calculate the focus point and some
    recommendations for F.L. versus diameter.

  2. Yes, there are formula for calculating Parabola Antenna Gain.... Google
    should get you those. The difference in parabola material is directly
    related to Frequency in that The mesh size needs to less than 1/4 of
    wavelength in order to be effective as a reflector. Solid is better.
    Antenna Feed System is a critical point in the design, as well as
    getting the feed system aligned with the dish's focal point. there are
    literally hundreds of 2.4 Ghz Gain antenna designs around the net. I
    would look at the Pringles Cantenna, and some of the cheaper Grid Corner
    Reflector types with simple Dipole Feeds. I use some nifty little Patch
    Antennas, on my 2.5 mile WiFi Links that provide LAN extensions, up and
    down the beach, for my Close Neighbors. (close + 10 Sq Miles)
  3. Bruce

    Bruce Guest

    Had done some looking and read up on various types. Settled on the
    parabolic as (hopefully) the type is not as directional as the
    Pringles Can type. Aiming the thing is a bit iffy without a sensitive
    signal strength meter. But of course, a tighter beam is higher gain
    The parabolic is actually easier for me to build as "wok" type cooking
    pans are a dime a dozen and in all sizes.

    Anyway, will do more research and see whether I can locate the gain


  4. Bruce

    Bruce Guest

    Yes, had that URL. But was interested specifically in gain versus
    diameter calcs. will look further. Thanks.

  5. Just as a thought, why not use a Sat TV dish. They are everywhere. Just about the right frequency and they are parabolic. Be sure
    to move the receiver element to the dish center, as they usually have a 30 degree included angle built in.
  6. Bruce

    Bruce Guest

    I would but I'm not sure whether I can buy just a disk. Most companies
    prefer to install a system :)

    I built a new parabola using a 17 inch aluminum "wok". Common as dirt
    here. The 17" was 225 baht (about US 7.25) and I used a 2 inch piece
    of 1" X 3 mm stainless for the mount and a piece of aluminum scrap to
    hold the active element.

    It appears to be more powerful then the previous model which was a 10
    inch strainer for frying bananas.

    If I had a signal strength meter I'd be in the catbird seat but I
    don't and suspect that for that frequency and power it would be more
    then a diode and single npn amplifier :)

    So, I can only try and see if I can pick up new stations and try and
    decide if it drops out more then the last one.

    I may try a corner reflector as I can bend up a big one out of


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