2.4GHz Wifi corner reflector 

First Harmonic (FH) was getting patchy wifi coverage to his desktop computer in his bedroom.  The obvious thing would be to invest in a new multiband wifi modem/router, one of those things that looks like a UFO with spiky antennas for its multiple bands.  But the situation presented a good opportunity for some basic UHF antenna experiments over this short unlicensed duplex data link. Discussion of the popular Cantenna suggested lower performance than many have claimed due to the small size of Pringles/Milo cans at 2.4GHz. A repurposed satellite TV dish of diameter 1.2m or more seems to be the best option.  Not having one, and needing a solution that would not turn FH’s bedroom into a junkyard, I opted for a homebrew corner reflector based on one of the many online designs.

First, I lashed up a cardboard and alfoil structure to act as a reflector, and while it seemed to make some difference, it was physically difficult to support.  Some kind of stand and semi permanent reflector was needed.  I went looking for a suitable reflector. Sheet aluminium from the hardware warehouse was too expensive.  Whilst shopping for dinner one night I found a cake cooling rack for $6.  To support it I made up a vertical stand from pine and hardwood dowel.

After knocking off the wire supports, the mesh was bent at right angles and cable tied to a pine base. The dowel was positioned right at the focal point of the 90 degree reflector as indicated on the template.  Once in the bedroom, the wifi dongle was taped to the dowel in front of the reflector mesh. The advantage of using a dongle is that it runs USB (not RF) from the transceiver back to the computer, so no losses. The disadvantage is that the dongle’s tiny internal antenna is probably inefficient.

To aim the reflector at the wifi modem at the back of the house I needed a reasonable wifi S-meter. We installed Wifi Scanner eval version.

Wifi Scanner shows signal strength for each network in dBm and updates every few seconds.

Signal strength went from about -90db before installing the reflector to about -82 to -84db.  This is about what can be expected from a passive corner reflector.   Rotating on its azimuth, it was about as sharp as expected for a beam of this type.  I did not do an A/B comparison on strengths of all the other neighbourhood networks but you would expect some to come up and others to drop as a result of adding the reflector.    

Speedtest showed 0.4 and 6 Mbps up/down with the reflector in place, with the house’s physical ethernet plugged in we get 0.7/8. 

Outcome… one online and happier FH. Job done.

There are many excellent yagis, dishes and collinears for turning domestic wifi into point to point links over multi-kilometer paths.  This little experiment was just a start. Perhaps it planted a seed in a young mind.


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