Best Homemade 802.11 Antenna? Calling all electrical inclined people.

Discussion in 'Community' started by coopdog, Nov 15, 2003.

  1. coopdog macrumors 6502a

    Joined:
    Oct 5, 2002
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    The Great Midwest
    #1
    I went "war driving" for the first time last night. It's a really fun thing to do on a boring friday night. We wern't doing the hacking kind of war driving where you try to exploit and find the backdoors and weaknesses in a wireless network then post the GPS online for other hackers.

    We did it with my friends ibook and a 12V to 120V inverter. It was fun, we went up to one of our friends houses and got on his airport and could talk to him on ichat with Rendezvous.

    We used the app Macstumbler to find the open networks. It works pretty well. But the antenna on the ibook isn't very powerfull at all and turning the iBook just a few degrees or moving in from the dash to my lap would loose the signal.

    I really want a way to boost the signal. But most of the antennas out there are $100-$500 for med range ones. I never buy something I can make myself, so I invesigated home made 802.11 antennas.

    Here's a site that lists all the major homemade designs.

    http://www.saunalahti.fi/elepal/antennie.html


    Here are the most popular designs with full steps and photos.

    http://www.turnpoint.net/wireless/cantennahowto.html

    And to one design that claims to go 10 MILES w/ line of sight!!! Thats huge!

    http://www.wwc.edu/~frohro/Airport/Primestar/Primestar.html


    But most, like the 2 links above are pretty directional especialy the 2nd one. I'm looking for a somewhat uni directional antenna, the more beam spread the better. I don't really care about size just so it can fit in the back of an SUV.

    Hey it snows here so you got to have one. Even the cop cars are SUVs.

    Anyway can any one with some electronics background give me some advice or point me in the right direction.

    Remember I AM NOT using this for hacking or anything of that nature. Maybe even for good, call up the buildings that have an open network and tell them that they are open to hackers. :D

    Maybe even make this a Macrumors project :D

    Thanks Guys!
     
  2. coopdog thread starter macrumors 6502a

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  3. kaosfere macrumors member

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    Nov 1, 2003
    Location:
    Chicagoland
    #3
    The cantenna is a classic for ham operators working on the microwave bands. You can't go wrong with its simplicity. However, it, like most external WiFi antennas, is a directional model -- it trades bad reception from most directions for good reception from a specific one. This kind of antenna is ideal if you have already isolated a signal, but not the best if you are trying to *find* one -- for that, you want something omnidirectional, or close to it.

    This is a design for a very good vertically polarized omnidirectional antenna with positive gain characterisitics. It is a bit complex, though. Here's a simpler plan for a similar, but less fancy, antenna. The J-pole is another very good omnidirectional antenna design, although I think it may be impractical at frequencies this high.

    The double-quad that is shown in one of those links above would not be omnidirectional, but would, I believe, be bi-directional if you removed the reflector from it. However, doing so would remove an impedance from the emitter, and require recalculation of the dimensions.

    A good book for you to check out would be the ARRL Antenna Handbook. It's designed for hams, but it is a great general-reference book both for theory and for specific designs.

    Hope this helps.
     
  4. coopdog thread starter macrumors 6502a

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    Oct 5, 2002
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    #4
    Thanks for the great post
    kaosfere!

    I think I'm going to try the can first, its much easier than the others. I'm now wondering what would be better a long can with a small circumference, or a can thats shorter and has a bigger circumference.
    It seems like most things longer and bigger around are better for radio signals get better reception. But I'm thinking there is a limit like a cantenna thats 6" by 2' would get the same or better than one that is 2' by 4'?

    I was thinking maybe some small duct work (like for forced air heating and cooling) maybe 1 foot diameter from homedepot and put a duct cap on the end. Then try differnet lengths.

    I was thinking the same thing about taking off the cap and making it hit 2 directions. Or even making a few cantennas to get more of a 360 degree spread. But that would create a lot of interference and the cables arn't cheap, my friend just bought a kit off ebay for about $27 w/ shipping. It comes w/ everything but the can, cheapest thing we could find.

    Also you need the cap on the end. My understanding is that it stops the waves from just going through and bounces them to the connector. Also I think you also need to do a calculation to figure out how far away you mount the connector from the end cap.

    Is there any way to amplify the signal like add circut to it with a power supply?

    I have thought about doing this, but I can't find any site that makes them or makes any tech sence to me atleast. Can't any radio or microwave be amplifed? But I guess you can't have a weak outgoing signal and then a strong reciver and get good results? :rolleyes:

    The cable should get here on friday so I should start to build it soon. Ill try and post some pics and maybe some wardriving ones too. :D

    Oh I just found this, it's a guy that used a coffee can short and deep and wide:

    So I guess thats pretty good. I found out that my friend w/ the ibook that we used last time, his built in antenna sucks. He only gets about 30% by his apple base station. The airport wire is smashed and fraied by the screen going back and forth. So I guess with any external antenna we should see great improvement.

    Thanks For ALL the help!
     
  5. kaosfere macrumors member

    Joined:
    Nov 1, 2003
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    Chicagoland
    #5


    You're welcome. Always glad to gab radio.

    If by "better", you mean more signals, you want to go with a wider, narrower reflector. If you were trying to build a highly selective antenna, you would want long and narrow.

    I'm not an expert on microwave antennas, having worked mostly on the HF band, so this info should be double-checked by looking at a detailed theory website, however I think that you're correct on both counts. The effectiveness of the cantenna is pretty much diminished by not having the end cap. That sort of antenna is what's considered a "waveguide" -- it relies on the fact that microwaves are blocked efficiently by metal to "funnel" the signal to where it belongs. Without the endcap, the signal will more or less pass through -- you'll still get any signal that does go through, but it will be much weaker.

    As for the distance of the end cap from the driven element, if I remember right (it's been about a decade since I read up on the theory much), as long as the end cap is sufficiently far enough away to prevent coupling with the emitter, that's all that matters. For best performance, you will want it, I think, to be at around 1/4 wavelength which, at 2.4 GHz, is just a little over an inch.

     
  6. coopdog thread starter macrumors 6502a

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    #6
    Thanks again kaosfere!

    The 802.11 cable is supost to get here today via UPS. My friend an I are planing to build it today. Ill try and take some pics! Thanks again!
     
  7. kaosfere macrumors member

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    #7
    No problem. Good luck, and let me know how it goes!
     
  8. coopdog thread starter macrumors 6502a

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    Oct 5, 2002
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    The Great Midwest
    #8
    The Results.On!

    We built it! It was $4 for a can, and about $17 on ebay for the wire and connector that goes on the can. So pretty cheap for the boost in power.

    The first time we went war driving just with the iBook built in antenna we got about 40 networks with about 4 hours of driving. It was quite annoying because I had to hold up the ibook the whole time and when I kept it in my lap I got no hits at all.

    Now with the homebuilt $20 cantenna we got GREAT results!!!

    With about 2-3 hours of driving the same roots we did the first time when we only got 40 hits, we got almost 500!!! If I remember right only about 1/40 were password protected. We tried my friend's house and from the road to the house is about 200 feet then through a brick wall and a few walls in the house to the airport. We were able to get a signal and get on the net.

    Driving 45mph I was able to get 25+ signal power.
    Some houses we were able to get 45+ signal strength with only about 5 noise. That’s better than using the iBook antenna 5 feet away from the airport in the same room! We were able to get a free wireless access point in downtown SLC from about a mile away! Later we went downtown and got up to 8 different networks at one time with about 25 signal each. At the free wireless access point the connection maxed at 52 signal and hardly any noise.


    Driving on the freeway going 70 for about 5 min. and no buildings near by
    We picked up 15 networks.

    We did some tests to see if the cantenna really did anything:

    Standing about 3 feet away from an Apple Airport we got signal strength in the 90's, with no can attached, just the wire, it was in the teens.

    With a signal strength of 30 I turned the can around to see if the signal could still be received from the closed end of the can, Yes! The signal went down to about 15. In all the cases the signal went down about half with the can reversed. Inside the house with 2 airports, one up stairs and one down I was getting about 70/30 signal strength from them no matter the direction of the can. So if your already inside a wireless network turning the can will not effect the signal that much. However if it is aimed at the base you will get a better singnal (5-10).

    I would say the cantenna is a Unidirectional antenna. Of course the signal is better if the can is aimed at the actual source, but it will pick up from both sides of the can or for war driving both sides of the street.

    Getting about 45 signal, putting my hand in front of the can dropped the signal down to 15.

    At my house I was able to get one of my neighbor's networks at 30+ strength. Both of my neighbors are about 100' away not to mention all the walls the signal has to go through.



    If you have poor wireless reception in your house, want a GREAT antenna for war driving or any anything, make a cantenna!

    Pictures, screenshots, walkthrough coming soon!
     
  9. MacPulse Zack macrumors newbie

    Joined:
    Dec 12, 2002
    Location:
    Jacksonville, FL
    #9
    Awesome, I'm looking forward to the how-to :)

    I need to burn a directional signal through about 600ft of dense pine trees... according to my calculations two cantenna's with a 36dBi gain will cut it... giving me about 50% strength on both sides.

    I'm interested in your cantenna design and the connectors you used.

    -Zack
     
  10. superbovine macrumors 68030

    superbovine

    Joined:
    Nov 7, 2003
    #10
    there is a great article in fall edition of 2600. it contains plans for an optimal canatenna using a geriatric tennis ball can.
     
  11. coopdog thread starter macrumors 6502a

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    Oct 5, 2002
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    The Great Midwest
    #11
    Pics, Graphs, Screenshots, Logs, UP!

    Pics, Graphs, Screenshots, Logs, are on the net now!

    This is a graph of one of the logs iStumbler made. We don't have a log of all the connections because iStumbler had a bug where it would delete the log after 10 min so it did fill the memory. The graph is of only about 170 logged networks:
    Graph of the wardriving results. Pretty Cool

    One of the screenshots we have. This was by our school. It was about 200' up to maybe 400' from the car to the actual base stations, through a thick brick and cinderblock wall then any internal walls. So very good! The log on the left side: The signal strengths are low because iStumbler doesn't record the max signal just the last recorded.:rolleyes:

    Here are 2 logs that we saved:

    Log 1

    Log 2

    The "encounter signal" Is not even the max singnal strength. It's the last recorded signal strength detected.

    Here are the Main pics
    I'm the pics of "Cooper" are me, and the pics that of "me" are my friend.
    I didn't take a shower for about 2 days so I look pretty scraggly. Thats not how I normaly look, I hope. :)

    Enjoy!
     
  12. coopdog thread starter macrumors 6502a

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    #12
    I have seen cantennas like that or made out of pringles. But on a few of the cantenna sites they say that because they are not metal they allow the waves to pass through. It's very logical too. If you cover the front of the cantenna with metal the signal goes down to about nothing, however if you cover it with plastic or a lid it doesn't do much to the signal. It's also the same idea that the waves can pass through walls, glass, solid things like that but not metal sheilding in buildings. So a metal cantenna is much better than a plastic, or paper one.
     
  13. coopdog thread starter macrumors 6502a

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    Oct 5, 2002
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    #13
    I'm not sure how well a home made cantenna will work for you. Is their a line of sight between the two buildings excluding the trees? I think you will have to go with a commerical solution especialy if you want desent speed.
     
  14. g5man macrumors newbie

    Joined:
    Oct 17, 2003
    #14
    I noticed you hooked up the antenna directly to the airport connection inside the I book.

    Do you happen to know if I could connect it to the back of my G5 and replace the antenna that came with it?
     
  15. SiliconAddict macrumors 603

    SiliconAddict

    Joined:
    Jun 19, 2003
    Location:
    Chicago, IL
    #15
    Behold the power of cheese….I mean nerd. I just hit my 2000th AP in October and I only started in late July. Been sort of slacking lately. My current tally is 2083 :-\ I was aiming at 3K by Dec 31st but its going to be a stretch at this point.
    My rig consists of a Dell Latitude with a Pharos GPS unit to capture the data with an external antenna. That sits on the floor of the car. And a Toshiba laptop sitting passenger with a BT GPS unit sitting in the back window. (Contrary to popular believe the amount of interference from BT radios is negligible and with a roof mounted antennal almost nonexistent.) The reason for 2 laptops and GPS units is the Toshiba allows me to use the below maps to know where I’ve stumbled before so I don’t end up backtracking. MapPoint for the PC is godlike software. I’m amazed every day by the fact it was created by Microsoft. This is the primary reason I’m waiting for a G5 laptop to become my first Mac since my ][e days. I need Windows and MapPoint to remain at an acceptable speed and hopefully VPC 7 coupled with a mobile G5 will do this.
    I see wardriving like collecting baseball cards. It’s a fun pastime even though the amount of gas you can go through in a week doesn’t speak to highly to my respect for the environment even though I consider myself a major advocate for cutting air pollutants. (I’m sort of fond of breathing you know?)

    I personally would highly recommend breaking down and shelling out the 90$ for a solid external antenna. http://shop.netstumbler.com/customer/home.php

    This is the one I have. I’ve made several of my own and while they catch a signal decently this thing owns. One thing about wardriving. It not so much about range. Range is good but also about accuracy. If you are sniffing a network’s AP a 1/2 mile away, and in most cases you aren’t going to be able to do this, the results you gather aren’t going to be messed up. That’s assuming you are gathering GPS data. If not then more power to you :)
    Anyways this is one addiction I don’t think I’m going to be giving up anytime soon. Its too much fun.
     

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  16. SiliconAddict macrumors 603

    SiliconAddict

    Joined:
    Jun 19, 2003
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    Chicago, IL
    #16
    One of my better war trophies from driving. Guess what MSFT stands for. :D
     

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  17. MacPulse Zack macrumors newbie

    Joined:
    Dec 12, 2002
    Location:
    Jacksonville, FL
    #17
    Nice!

    I'll take a guess: Microsoft

    ?

    :)

    -Zack
     
  18. coopdog thread starter macrumors 6502a

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    Oct 5, 2002
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    The Great Midwest
    #19
    My friend found an app for linux that after about 10min or so of packets it can find out the WEP Password! I might try it on his or my network, never on anyone else's. :D
     
  19. MacuserMiller macrumors newbie

    Joined:
    Jan 12, 2004
    #20
    Airport antenna connector type?

    Hey thanks for all the helpful info on the antennas. I was wondering if anyone know what type of connector the airport card has that goes in the slot loading imacs? I was going to try to connect an external antenna to the card directly. Thanks for all your help!
     

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