Necessity is the mother of invention so I've been a busy bee. With no Internet of my own, I have to sniff out spare bandwidth on the passing ether.
I built a cantenna a few months ago. While it did give me a good directional wifi antenna the improvement in signal strength was not always that good.
During my daily Internet research for a better and/or cheaper life I happened upon the bi-quad antenna. I read of an impressive signal improvement so I had to see for myself.
I won't go into too much detail as to how I built the antenna so for precise details go to the link at the end of this post. Here, I present how I achieved the same results as others using just what was available to me. No money was spent converting what I had around me into a double bi-quad antenna.
Sitting on my wardriving netbook we see the completed double bi-quad, so called because it consists of two bi-quad antennas interlinked. The reflector plate is an old PCB that had a circuit partially inked onto it but I soon had that off with a Brillo pad.
Here we see the centre of the antenna, consisting of an N-type chassis mount connector held in place with four bolts, which are shielded from the reflector plate with some plastic from a discarded shampoo bottle. The reflector plate plays no electrical role (or maybe it does - see comments) in the antenna so it has to be shielded.
The antenna wire is made from a 1mm thick copper wire taken from thick mains cable. Each side of the four diamonds of the antenna array is supposed to be as close to 30.5mm as possible, which is one half of the wavelength of the 2.4GHz wifi signal.
At no point should the wire touch itself, especially at the crossover points. The wire ends are then attached to the N-type connector. One end was soldered to the centre of the N-type and the other end was held between two washers on one of the mounting bolts. The mounting bolts are electrically connected to the ground of the N-type and complete the circuit to the wifi adaptor.
Here we see the rear of the reflector plate with the N-type bolted in place.
To connect the bi-quad antenna to your wifi adaptor you will need an N-type to SMA adaptor as pictured above.
Remove the supplied stick antenna from the wifi adaptor and screw on the N-type to SMA adaptor.
The wifi adaptor and bi-quad antenna can now be attached to each other and thus linked to the computer.
Note that the wifi signal will be polarised much like a satellite signal so the antenna will need to be rotated (as with the LNB on a satellite dish) to get the best signal.
Here are two screen grabs from NetSurveyor showing the improvement in signal with a bi-quad over the standard stick antenna.
The stick antenna is omni-directional and the O2wireless router that i was connected to gave a signal strenth of -59dB.
The bi-quad is more directional than a stick and by pointing the antenna directly at the router the signal improved to -58dB (a doubling in signal strength). Power increased from 1.26mW to 1.58mW.
The bi-quad antenna will have a dual use; for connecting my computer to the Internet and also for making Skype calls on the move.
Here we see my two Skypephones. The one on the left is a Three network phone that I can use for free (whilst in the UK or Ireland) to call any other Skype user. For countries (such as Spain) where there is no free Skype access over a 3G network I use the Belkin wifi phone on the right. My parents have another Skypephone in the UK with which we can keep in contact for free.
The only problem with the Belkin wifi phone is its poor internal antenna, which means I have to sit next to the router that is "donating" access to the Internet. With the case off the Belkin wifi phone we can see the antenna (highlighted with the red box at the top). I have two options here. I can replace the internal antenna with a connector to allow me to plug in the bi-quad antenna. However, this will make the phone cumbersome and could ruin it altogether.
The second alternative I am going to pursue is to cheaply buy an old secondhand Linksys WRT56G router from eBay, which can be updated to make it into a wifi repeating station. The bi-quad antenna feeds the repeater, which then acts as a strong access point next to my Belkin wifi phone.
MartyBugs.net - BiQuad Antenna Construction
Lifehacker - Turn Your Old Router into a Range-Boosting Wi-Fi Repeater