Simple Directional WiFi Antenna

Wifi Antenna

Back in 2007, [Stathack] rented an apartment in Thailand. This particular apartment didn’t include any Internet access. It turned out that getting a good connection would cost upwards of $100 per month, and also required a Thai identification card. Not wanting to be locked into a 12-month contract, [Stathack] decided to build himself a directional WiFi antenna to get free WiFi from a shop down the street.

The three main components of this build are a USB WiFi dongle, a baby bottle, and a parabolic Asian mesh wire spoon. The spoon is used as a reflector. The parabolic shape means that it will reflect radio signals to a specific focal point. The goal is to get the USB dongle as close to the focal point as possible. [Stathack] did a little bit of math and used a Cartesian equation to figure out the optimal location.

Once the location was determined, [Stathack] cut a hole in the mesh just big enough for the nipple of the small baby bottle. The USB dongle is housed inside of the bottle for weatherproofing. A hole is cut in the nipple for a USB cable. Everything is held together with electrical tape as needed.

[Stathack] leaves this antenna on his balcony aiming down the street. He was glad to find that he is easily able to pick up the WiFi signal from the shop down the street. He was also surprised to see that he can pick up signals from a high-rise building over 1km away. Not bad for an antenna made from a spoon and a baby bottle; plus it looks less threatening than some of the cantenna builds we’ve seen.

45 thoughts on “Simple Directional WiFi Antenna

  1. I’m impressed, That shouldn’t have worked. first, you don’t know if the spoon us actually a parabola, second, he’s assuming it is and doing the math as if it were. third, cantennas have to be tuned as they are built, how he got any signal at all is a miracle. great job!

    1. Reflector antennas are much more forgiving than a waveguide antenna. The critical point in the cantenna is the coupler between the coax from the card and the waveveguide (soup can). A reflector, as long as it has nog holes larger than about of 10th of the wavelength will reflect the signal. The feeding antenna in the dongle is probably ill shaped, as it will be omni directional instead of aiming the signal at the reflector, but it will still work, albeit with a distorted radiation pattern and somewhat less gain in the broadside direction.

    2. It probably doesn’t work. Just the fact that he set the dongle outside was probably the key.

      I’ve never had any luck with these things. If the connection is slow and breaking up, it’s still going to be really sketchy even with pringles cans and wok pans or whatever, and you can pick up wifi SSIDs from a kilometer away if you have a clear line of sight without any of these.

      1. While I haven’t built an outdoor one before, I have used a large wok as parabolic reflector and smartphone running a WiFi signal strength app at its focal point to determine that upwards of 25dB gain is possible with such a setup.

  2. Im a little sick of seeing “Super simple and cheap directional antenna!!!” everywhere. Almost anything metal works as an antenna, and placing grounded metal stuff behind it gives it some level of rejection to background signal, but this designs are not really a parabolic antenna. A parabolic antenna needs a real parabolic reflector with a real calculated shape, and an absolutely exact location for the antenna in the focal point of the parabola, everything else is an “antenna with metal behind that kinda gets wifi signal”, but no more than that.

      1. The benefits of WokFI are well documented.

        Once upon a time in college without money for my own broadband, I shared it from a friendly neighbor a thousand or so feet away in another community.

        I should just submit my old hacks instead of letting my comrades pick from the tips line, here’s mine, a bit more of a hack than the one in the article:

        So, there’s a lazy susan bearing, an old DirecTV dish from the days before “grey market” satellite receivers became black that everyone then ripped out, a trusty old WRT54G with DD-WRT on it cranked up from 30mW to 250mW (square hole cut and scrap PC fan screwed to the case), and WindSurfer cardboard+gluestick+tinfoil directional antennas.

        Gut the feedhorn, point the WIndsurfers back into the dish, flip the dish upsidedown and bolt it to the arm backwards, and have the dish pointed what looks like awkwardly downward (angle is really about 20-30 degrees steeper that what you presume it to be, so the feedhorn doesn’t block line of sight).

    1. Agreed. When I was a kid (maybe 8-10ish?) Dad taught us how to graph parabolas in Lotus 1-2-3 and we printed a couple wider ones and bent sheet metal into the shape of the graph. Then he taught us how to find the focus point by drawing lines and calculating reflection angle and we taped a microphone to the focus point.

      Long story short: we could hear the dog panting from 150′ away. It was pretty cool.

    1. Well, the parabola amplifies the signals like how a cone could amplify your voice if you speak through it, with the constraint of narrowing where the amplified signal is directed.

  3. While I agree with Eduardo to some degree, in this case, close enough is good enough.

    The design could no doubt be improved and the gain increased by making the spoon “more paraboloc”, but for the wavelengths in question, this rough shape is near enough.

    If you look at all the bashed and distorted satellite dishes in the world that sitll manage to receive a signal you will realise that there is a fairly large margin of error in a parabolic radio reflector. Light reflection in a slolar cooker is another example of close enough is good enough. You wouldn’t get away with this much error in a telescope’s optics because you are trying to form a perfect image, but you do in the solar cooker or wifi antenna because you are trying to grab as much energy as possible.

    1. I think the ‘good enough’ is important as it comes down to the required tolerances (if you only need an 80% ‘parabola’ to get enough signal then why work harder?).. as I discovered having hammered a squashed satellite dish to what visually approximated a parabola and it worked far better than the flatter version :-)

      Even with optical quality you’re still only going for good enough (see kit-lens vs Nikkor/Canon-L lens) until you have a reason for needing more (although, much like demanding a perfect parabola spoon in this application, there’s always people demanding perfect results when it’s not required/perceivable).

    2. The loss of gain associated with ball-parking the location of the antenna in relation to the reflector is offset by the gain associated with the surface area of the reflector relative to wavelength. And it doesn’t have to be a parabola. There are many directional gain antenna designs that utilize non-parabolic reflectors. There are box-reflectors, corner reflectors… even the common Yagi or log-periodic is an example of this.

      If you’re going for absolute perfection and absolute maximum gain… sure, make a perfect parabola and place the antenna at the focus. But sometimes imperfect is good enough.

    3. A solar cooker is where you *do not want* a very fine focus, unless you like a tiny spot in the middle of your raw steak to be charred through, or holes melted in your stew pot.

  4. I’m not sure abouth that exact focal point, because if you use an ordinary wifi dongle it is omnidirectional so if you get the signal right on the dongle or 1 feet away there is no problem since you actually can receive a stronger signal. This is better for download, but for upload i’m not sure if this antenna can improve signal a lot..

    1. I have an Alfa with that huge omni antenna. Very disappointing. As claimed by the websites touting this combo, the sensitivity is incredible, and I can pick up 20-30 APs whereas anything else I have picks up 4-5 max. But sensitivity doesn’t equal selectivity, and with all those AP’s broadcasting over each other, the throughput when an actual connection is made to any of the additional distant APs is near zero. Merely making the AP list is far easier than useful communications, all you need is one uncorrupted SSID packet every few minutes. One of the software utilities recommended by sellers of this combo to display AP lists seems to accept corrupted SSID packets too, leading to a false list numbering in the hundreds, with multiple garbled versions of each AP; so take “Amazing, I can receive ### APs now!” claims with a grain of salt. This setup probably only works when there’s a few APs in the extended range, otherwise you need a directional antenna.

  5. ive had alot of luck with making these type things.. i took the case cover off a computer and flexed it out like this “\_/ and dangled my receiver in the v and it worked meant the difference of having and not having a connection

  6. I saw the Orcon site a few years ago and built this.

    Old parabolic lamp shade on a goose neck. I calculated the focal point, opened the dongle to determine the precise location of the antenna and placed it accordingly. I figure I get around 12db of gain. Also I’m surprised no one has yet to mention re-using old DBS dishes.

  7. Has everyone forgotten that a circular arc approximates a parabola for small angles of arc. So, as long as the spoon is somewhat spherical, it’s going to be very close to reflecting all the signal that hits it to and from the focal point.

  8. ” It turned out that getting a good connection would cost upwards of $100 per month”

    Meanwhile back in Australia, a mediocre ADSL2 connection with a 200gb cap that drops out when it rains costs $100/month..

  9. I absolutely adore topics like this.
    When I was much younger I had similar success with a 700Mhz video receiver and an umbrella I had covered with aluminum foil.
    I placed the transmitter at extreme range and fiddled with placing the receiver at different points until the signal got better then lopped off the extra handle length and wire-tied the receiver in place.
    I attached the rig to a camera tripod and kept it pointed at the RC truck the camera and transmitter were mounted to and that was my first foray into ROVs! :D
    Awesome times.

  10. I have a WiFi router on my wall with the wireless link setup to act as a virtual cable to the DSL modem. I put some aluminum flue tape on a piece of cardboard behind the antenna, gave it bit of curve. The signal strength improved a bit so I called it good enough.

  11. Wish I could hire one of you guys to help me get internet at my rural home. Here is my situation in a nutshell. No DSL available, No broadband and of course satellite is terrible. Currently we are using hotspot through AT&T and it’s a ripoff. Comcast has those public hotspots now (have to login I know). There is a house exactly .5 miles away down the road with Comcast broadband and one of those hotspots. Is there anyway I could pick up that signal? Any other ideas?

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