Long Range Parabolic Wi-Fi Antenna

Part 2: Completing the Helical Wi-Fi Feed - Mounting it on the Dish

This antenna can be constructed in a couple of hours and some measuring, cutting, bending, and bolting metal. Use caution around the sharp edges. When finished, put it up and enjoy a very durable antenna that provides great signals.

Here is a table used for my prototype helical wi-fi antenna and its connector. Note that turn 1 starts at 0.8 cm (height above ground plane of feedpoint). Turns Spacing is 2.5 cm, and the diameter is 3.9 cm (close enough for 1.5" PVC tailpiece). If your connector can be trimmed to allow a feed connection closer to the ground plane than 0.8CM, then simply run the helix as low as necessary. Most impartant is keeping the proper spacing between turns.

13. Carefully wind the helix, using circuit tape or wire, then solder to center conductor of chassis connector. Double check against the turns template. Polarization will be right-handed if the turns spiral clockwise (looking outward from feedpoint).

14. Attach the angle bracket and wi-fi adapter, making sure all parts are secure and ready for service, as seen in the images below.

At this point, helical wi-fi antenna is ready for its smoke test...plug in the cables and look for some signals! Theoretical gain of the prototype helical was about 18 dB over an isotropic radiator; it beat my biquad by about 7 to 13 RSSI units, and indeed seemed less sensitive to polarization and rainfall. Signals still seem to fluctuate much from second to second. If your antenna is functioning satisfactorily at this point, I suggest spray painting three layers of clearcoat onto the windings and groundplane for stability and corrosion prevention.

INTEGRATION WITH A PARABOLIC REFLECTOR

For very long range wireless networking, I have used a short 5 turn version of this helical wi-fi antenna, left hand polarized, to feed an 80 cm parabolic reflector. Signals were about 26 dB stronger than on a simple dipole! Mounting the helix was a matter of removing the original satellite TV feedhorn from the dish's focal point, then (using the angle bracket) bolting the helical wi-fi antenna into place. It was necessary to bend the bracket just a bit to aim the helix at the center of the dish.

Mounting the newly built parabolic wi-fi antenna was tricky - it required inverting the mounting hardware and angling the dish to about 75 degrees for peaking signals on the horizon. It rests atop a vertical length of 2" schedule 40 PVC pipe. The antenna is very directional! After not initially seeing much signal strength from a distant access point, the s-meter suddenly pegged full scale when I aimed it dead-on! Aiming properly in both azimuth and elevation is important with these large parabolic wi-fi antennas because of the narrow beamwidth. However, these narrow beams have two great advantages: interference is reduced and distant access points are reachable at fast connect speeds.

Note that a yagi, biquad, or "cantenna" waveguide feed would work well with a parabolic reflector, and would have a slight polarization advantage over a helical - but would show more sensitivity to polarization and rain. 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 DirecTV dish, it provided full-scale signals from otherwise weak access points. Many excellent designs are available on the world wide web. Find them. Then mount them on parabolic reflectors for long range wi-fi operation!

Good luck, and may you enjoy lots of long range wi-fi connections!

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