Cheap biquad antenna extends LAN between apartments

[Danilo Larizza] is sharing a network connection between a couple of apartments. They are not far apart, but they are also not right next to each other so a set of external antennas is necessary. He built this 2.4 GHz biquad antenna on the cheap (translated) just to test if it improved the signal before he tried to buy a proper antenna. It turns out to work well enough that this is all that he needs.

The antenna itself is about one meter of thick wire bent into two squares which are 31mm on each side. The coaxial cable going to the router connects to the center portion of this antenna. For a bit better directional reception he added some tin foil as a reflector. Since this is outdoors he used a food storage container for protection (the antenna is mounted to the lid, the body has been removed for this picture). The whole things is perched on a stake in a flower pot with proper line of sight to the other antenna.

We’ve seen a very similar design used for an NRF 24L01+ radio. If you need more details that [Danilo] posted that would be a good project to study.

Comments

  1. Justin says:

    SWR is sooo 1990’s

  2. wowme@wtf.com says:

    Even Danilo knows that it is aluminum, not tin,

  3. Matthias Welsh says:

    Cool that it worked out, but after designing and tuning quite a few antennas. It probably works, but if properly tuned up (spec-an/tracking gen) to where the VSWR settled below 2 it would be a kickass antenna. You may be able to cheat using a router with an interface that provides signal strength or RSSI and trim down the quads/stand off. No measured and cut antenna will be optimal off the bat.

  4. Linkdead says:

    I’ve built something similar with a copper clad board, some copper wire, and an RF connector. They work really well in pairs. I considered a more complex Yagi desgin, however these are faster to build with minimal parts to measure.

  5. PvreHaavok says:

    In Brazil you would be arrested and forced to pay a fine for this!

  6. A_Blind_Man says:

    wasn’t this done a really long time ago?

    http://www.engadget.com/2005/11/15/how-to-build-a-wifi-biquad-dish-antenna/

    take off the dish and add some sides to decrease the vertical beamwidth and you have a pretty decent ~13dbi of gain in a 45 degree beam horizontal (all depends how close to perfect you are.) If you can get your hands on some LMR 400 coax, use that of you have your router/computer more than a few feet away.

  7. az1324 says:

    “The antenna itself is about one meter of thick wire bent into two squares which are 31mm on each side.”

    31mm x 8 !~= 1m

  8. Erich says:

    Don’t forget, a dipole with a corner reflector or a helical circularly polarised antenna at each end are also very easy to build with not much more than some wire.

  9. You mean there are still people using 2.4Ghz out there :)
    If you want to narrow your beamwidth you can stack 2 biquads on top of each other.
    The diameter of the wire you use also has an impact on the frequency range and the distance of the termination points impact on the SWR as well as the distance of the element to the back plane. If you want to do something really different you can also use a biquad with rounded elements instead of square ones…
    Like OO instead of

  10. jpnorair says:

    My preferred approach is the good-old circular yagi-uda. In my opinion it is the easiest to manufacture to a high degree of precision, because you only need to find circular things of the right sizes to wrap the wires (or tubes) around. You can also use tape to fine-tune the inner-diameter. I have paint bucket wrapped in duct tape in my closet, for some of the 433 MHz ISM band Yagi-Uda arrays I’ve made.

    • Justin says:

      A tip if you ever decide to build one for 2.4: almost all wifi antennas sit vertically oriented. I built a 40 cm yagi recently and found out that the neighbouring ids dropped to a fraction when I positioned it horizontally. Odd but true.

  11. SteveHaD says:

    Pretty cool and seems to do the job, so that’s what matters the most. I’d personally want to find a way to make it look a little better. It wouldn’t be so bad if it wasn’t for the foil.

    While I do like the DIY route, it’s worth considering that an equivalent (likely better performing) yagi direction antenna can be had for about $5-$10 on eBay. So if all else fails, it’s quite cheap now days to get a decent antenna.

  12. MrX says:

    Man, biquads rock! Around 5 years ago I built a quarter-wave biquad for my parents, to improve reception of VHF for TV. The thing was nearly half meter wide but worked really well!

  13. FatTony says:

    It’s even from 2002: http://www.frars.org.uk/cgi-bin/render.pl?action=link&url=1064&goback=999999
    Built two of such antennas in CD-R trays with a friend to connect our houses with the great DLink AP900+

  14. metropolis says:
    • FatTony says:

      This is exactly the guide we used back then for our AP900+ Quad. We used some 50cm coaxial cable soldered directly to the AP PCB.
      Before we tried a tin can / Pringles antenna unsuccessfully.

  15. Slipster says:

    The antenna gain would be negated by the long run of coax. At 2.4ghz you lose signal very fast unless you run extremely expensive hardline. Best to place the router/wap/etc as close as possible to the antenna.

  16. ka1axy says:

    I did something similar for my brother, who wanted to share (with permission) his neighbor’s wireless internet. Two pieces of foamcore, cut to form a parabolic curve, which was then covered with alumin[i]um foil. A hole was pierced at the focus of the parabola, and the coaxial dipole antenna of the wireless adapter was inserted. Signal strength increased noticeably on the display.

    Some gain is better than none, but as says, you gotta minimize feedline loss, because most coax doesn’t perform well at 2.4G.

    For those considering longer paths, surplus satellite dishes work well, but you need to replace the feed with your 2.4G biquad.

  17. Manuka says:

    USB based “wokfi” approaches are simpler & usually superior to biquads,as only slow digital signals (rather than 2.4GHz RF) are in the cheap USB feedline. Check => http://www.usbwifi.orcon.net.nz for numerous DIY ideas

  18. There is also the ground plane model

    http://www.danilolarizza.com/?p=62

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