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
7 comments:
:O You have boggled and astonished me with your electronic knowledge and MacGyver skills.
My only real skill is as a researcher.
If I need to know, I know where to go.
Far too many people resort to their wallet, if they have a problem. I use my head and save thousands of pounds, yearly.
ur such an good at it. nice job
Just wanted to bring something to your attention as both your cantenna and double biquad solutions were an inspiration to me as I'm also using an Alfa AWUS036H and Google was kind enough to point me in your direction during my searches..
Your comment, "The reflector plate plays no electrical role in the antenna so it has to be shielded." is, I believe, simply incorrect.. Think about it.. Did you take measures to ensure that the N-type chassis mount connector was 'sheilded' in your cantenna build? You didn't mention it there but I imagine the answer is no.. The can acts in the exact same way as the reflector on a biquad, or in your illustration, double biquad design.. The can and reflector are the (-) negative connection of the antenna while the little stick of wire and the double /biquad are the (+) positive side of the connection.. Both are needed.
I came to this conclusion only earlier today while preparing my notes to build a double biquad myself primarily based on your idea of using the Alfa without a pigtail.. I was also referencing other builds of this antenna at - http://www.trevormarshall.com/biquad.htm and - http://martybugs.net/wireless/biquad/ and - http://www.lincomatic.com/wireless/homebrewant.html (scroll down about 2/3 of the page)
At Trevor Marshall's link, we can't see the connections very well..
At the martybugs link, which is a direct replica of Trevor's, we can see more clearly the connections.. the copper pipe is directly soldered to to the copper PCB.. Then, further down, the braid is crimped within the copper pipe creating the (-) negative bond from the wire to the copper PCB reflector.. I believe some solder between the braid and copper pipe would only help in that build..
In lincomatic's build,(2/3 of the page down) he shows how he didn't correctly connect the feed from the biquad element to connect to positive and negative even though his N-type connector was soldered to the backplate.. He then corrected his design.
I don't mean to come across as though I know anything at all.. I'm as amateur as I can be in this field.. I just wanted to point out a detail I found across several pages..
I myself, as I said earlier, was inspired by your build and so I did so today.. Build it that is.. I couldn't be happier..
Thanks for the inspiration.
Thanks for your comment Ken.
A few months ago, I considered what you have posted. I knew that the copper pipe (of other designs) was connected to the copper of the PCB and tried a little experiment.
I shorted the N-type to the face of the reflector plate to see if it made a difference. There was no increase or decrease in signal.
I have no idea why that should be so. I am a computer scientist, not a telecommunications expert so I will leave such matters to others.
I get a better signal than with a stick antenna so I can't complain.
Recently, I downloaded the latest driver for the AWUS036H and attained a further slight improvement in operation. You can download it here
http://www.alfa.com.tw/in/front/bin/ptlist.phtml?Category=105397
hi man you say
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 washer " abo yo make it clear you say the distance to the reflector needs to be 15 mm you say but when you bend that one end to the washer it gets closer to the reflector and we can't keep the expected distance to the reflector ro what do we have to do
The reflector is the diamond array not the leads from the reflector array going to the N-type.
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