Long Range Wi-fi Dish Antenna
THIS INEXPENSIVE WI-FI DISH ANTENNA OUTPERFORMS ALL OTHERS!
Presented here is a project showing how to convert common satellite TV antennas into high performance wi-fi dish antennas. If you intend to make multi kilometer wi-fi connections, this is the antenna type to use. With a high power wi fi adapter this kind of antenna is fantastic. Such a large 2 or 3 meter diameter wi-fi dish can provide 802.11 connections to access points dozens of kilometers away (if the path is line of sight). Satellite dishes are easy to convert into wi fi dish antennas. The essential change is replacing the satellite TV feedhorn with a modest directional wi fi antenna. None of the manual "curve making" of scratch built parabolics is necessary. One does need a C or Ku band reflector in good condition and basic tools for measuring, cutting, and bolting parts.
Obtain a parabolic reflector designed for C or Ku band satellite television service. These are now inexpensive and abundant. The wi-fi dish pictured above was built from satellite TV gear discarded by a local resident. Similar reflectors can be found in thrift stores, flea markets, and other habitats of electronic scroungers. Seek moderate to large reflectors (at least 76 cm or 30 inches diameter), since these will provide greater gain and directivity. Use a reflector in good condition and free of dents!
BUILDING A FEED FOR THE WI FI DISH ANTENNA
For very long range wireless networking, I have used a short 5 turn version of the helical wi-fi antenna, left hand polarized, with an 80 cm parabolic reflector. Signals were about 26 dB stronger than on a simple dipole! Mounting the helical wi-fi antenna was a matter of installing an angle bracket and bolting the helical wi-fi antenna into place at the dish focal point. It was necessary to slightly bend the bracket to aim the helix directly into the dish.
Another wi fi dish antenna feeder option is a 3 or 4 element yagi mounted at the focal point and aimed into the reflector. Yagi feeders are simple to construct, durable, and effective.
Note that a wi fi biquad, biquad, or "cantenna" waveguide feed would work well in a wifi dish antenna, and would have a slight polarization advantage over a helical - but would lose more signals in rain and not work as well with signals reflecting off of buildings, hills, vehicles, etc. The biquad wi-fi antenna pictured below was built out of junk parts one afternoon, and enabled very good long range 802.11 connections on its own. Mounted at the focal point of a surplus DirecTV dish, it provided full-scale signals from otherwise weak access points.
A small wi-fi dish, using a cantenna feed.
The mount needs to be inverted!
Another small wi-fi dish, using a biquad
MOUNTING AND AIMING THE WI FI DISH ANTENNA
Installing a wi fi dish antenna is more complex than it seems. Consider how the antenna will be used: for a fixed point-to-point link, scanning the area for usable free hotspots, or a portable link back to one's home access point? A fixed antenna can be aimed and bolted into place. A steerable or portable dish needs a means of securely mounting and aiming (motorized or by hand).
Offset feed antennas originally designed for modern Ku band digital TV require special mounting and aiming technique. The best method is to invert the mounting hardware and angle the dish to about 75 degrees for peaking signals on the horizon. In azimuth, aim directly at the desired access point, but in elevation, offset about 37 degrees. The webmaster's antenna stands atop a vertical length of 2" schedule 40 pipe. A prime focus wi fi dish, on the other hand, can simply be mounted on a pipe and aimed directly at the signal source.
These wi fi dish antennas are very directional! It is common to scan an area and see weak signals just barely detectable when out of the beam. As the antenna is aimed directly at the distant access point, the signal strength will jump up considerably - perhaps to full scale. High directivity associated with wi fi dish antennas is good: interference from off center stations is reduced and distant access points are reachable at broader bandwidths.
All of the parabolic wi fi antenna feed types discussed here are intended for connection to USB wireless adapters. Yes, extended range connections are possible with a simple USB wi fi adapter mounted at the reflector's focal point, but for maximum performance, the adapter must have some kind of directional antenna directly feeding the RF circuitry. Make it easy, and find a wireless adapter with a removable external antenna. Then, unscrew the original and replace it with the yagi, helical, or biquad homebuilt antennas. Mount this at the reflector focal point and go for those cross-town or cross-county links.
As to getting the wi fi data into the computer, use USB extension cables for the shorter runs. Powered USB hubs can be used for longer runs when the computer is 15 or 20 meters away from the wi fi antenna. One user actually mounted the antenna outdoors, on a rotator, and connrcyed three sets of hubs and USB extension cables to reach is office computer. He then had access to five full strength wireless hotspots and was never without free (as in beer) broadband. In another case, a farmer set up an attic mounted indoor parabolic, by a window, for wi fi access to another of his buildings. He used two powered USB extensions (essentially a data repeater built into the cable) to reach his desktop system and have wireless broadband.
Good luck, and may you enjoy lots of long range wi-fi connections!