TechIdiots Forum

I have built two "Cantennas", I mean, "Waveguides". One has just a slot cut in it with a D-Link WUA-2340 USB wifi adapter stuck in, and it works surprisingly well. Similar to this: http://aircrack-ng.org/doku.php?id=cant ... _with_gain

The other waveguide is constructed with an N-connector antenna like this: http://www.lincomatic.com/wireless/homebrewant.html

My idea was, instead of using a long, lossy coax (pigtail) to connect from a wifi adapter to the N connector/antenna on the can, I obtained a short 12" pigtail, and will be mounting a different USB wifi adapter on the can with sticky back velcro, and connecting that to my laptop with a long USB cable.

I purchased a USB wifi adapter which looked to be just the thing I wanted. It had an RP-SMA antenna connector mounted right on the end of the USB stick, so no modifications to add a tiny fragile connector. Further, the USB adapter was 300 mw, instead of the usual 30 mw or so power. That's nearly 1/3 of a watt!

Now the problems begin. I have an HP laptop with Vista Home 32-bit. I installed the driver plugged in the new 300 mw USB stick, and I can't connect to my own router just 6 feet away.

After reading up on the problem on the net, it seems that this Realtek RTL8187 chip set has a serious problem with obtaining an IP address from the router with Vista. Apparently Realtek has not done their homework. I finally got connection by entering an IP address on the computer end, which for my D-Link Router would be 192.168.0.xxx, with the last three digits from 101-199. I entered 199. I also had to enter Subnet as 255.255.255.0, and for Default Gateway, DCHP, and DNS, 192.168.0.1 (for all three). Now it connects immediately.

At this point I have not used an encryption key or MAC filtering. I had temporarily turned off MAC filtering.

I read the MAC address off the the label pasted to the USB stick, entered that into the allowed MAC addresses for the router, and ... no luck. Would not connect. Just to insure that I had the correct IP address, I went to a cmd promp, typed in IPCONFIG/ALL, and what do you know? the MAC address for my device was wrong. The last two characters on the label are 1E, but the correct last two characters are 15. I edited the MAC address in the allowed MAC's in the router and BANG! I am online with MAC filtering.

At this point I still can't make this Realtek 8187 device connect with Automatically Detect IP setting. Yes, I have the very latest driver directly from the Realtek site. I won't go any further with encryption keys at this point.

If anyone has a clue, I am all ears.

Did you try using a older revision of you driver? like this person http://www.hardforum.com/showthread.php?t=1140003

Thanks, AC... went to that Majorgeeks site, downloaded the 1221 version. I had found that before but hesitated to try it as it did not have a Vista driver in the folder. Having nothing to lose, I tried it anyway.

I went into Device Manager, right clicked on my Realtek 8187 USB adpt, chose Uninstall. Then clicked to unstall driver software.

I unplugged the USB adapter, plugged it back in, it appeared in Device Manager under Other Devices. Immediately got the Found New Hardware popup, and chose to browse to find driver. I browsed to the v.1221 folder's XP subfolder and selected that. Next, a popup warning that it was unsigned. I chose to install anyway. Then a message that it installed successfully.

I clicked the network icon in the systray, clicked Connect to Network, and Voila! I checked in Properties, and sure enough, it is working with Obtain an IP Address Automatically, and Obtain DNS Server Address Automatically.

So, apparently Realtek fixed something that wasn't broken. The older XP driver works just fine under Vista. The new Vista driver is the problem (as are many new Vista things).

So, now I have a 300 mw USB stick, a Cantenna, and Vistumbler... I am ready to rock!

Thanks, Al!

awsome... I would love to see a picture...

I need to do a little painting first. Will take a pic.

Right now my other cantenna, the one with the USB stick stuck directly into the can, is over at my neighbors. Last Friday (always this before a weekend, huh?) tree trimmers from the county came through and cut the phone line going to my next door neighbor. No phone, no net (DSL).

She's elderly, a widow, and likes to chat online with family every night.

I went over and hooked her up with my cantenna. Took less than 5 min to install the driver, aim the cantenna back at my house, and get her online via my router.

She is on the far side of her house from my place. The cantenna is getting a signal through all of those walls, and several walls of my house. But she has a 36% signal and that's enough. Connection seemed as fast as I get at home.

Is this cool or what?

Gee, NOW you tell me!



OK, how to post photos?

1.) Click the post reply button
2.) Click Upload attachment
3.) Browse for file
4.) Add the file
5.) Submit Post

Thank you, Andrew!

For WiFi at 2.4 ghz, use a can 3.25" (82.6 mm) diameter. The bandwidth of the can is related to the diameter. A 3.25" diameter has the 2.4 ghz WiFi band centered in it's bandwidth. I used two 27 oz white bean cans.

There are directions on the other details here:

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

and here:

http://www.lincomatic.com/wireless/homebrewant.html

Both have calculators to get critical dimensions. For example, the antenna stub should be 1.21" long (31 mm) and for a 3.25" diameter can, should be 2.5" (63 mm) from the back of the can.
Pop rivets will be used to attach the N-connector with antenna stub. I can't get my hands into a 3.25" dia can to install with screws and nuts.


At WiFi frequencies coax is very lossy, so a short 20" pigtail was used. To get needed distance from computer a 10' USB Male A to Female A extension cable was used. This keeps RF power loss to a minimum. I got this pigtail from Your WiFi Guy store on ebay, ebay seller name urwifiguy. They also sell a kit with a 6' pigtail and two N type antenna connectors already made up. The short pigtail was added to my order for only $6 more.

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0153104060
This is a USB WiFi adapter, 300 mw power. I got it from the DataAlliance store on eBay, eBay seller name data-alliance. It has a RP-SMA connector on the end, which is the same as on many wireless routers for the stubby "rubber ducky" antennae.

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0210380573
I sprayed the can with some medium gray Krylon paint. It is very fast drying. Next I attached the N-connector antenna with poprivets. Then attach the male N-connector on the pigtail to the female N-connector on the can. Attach the RP-SMA connector to the USB WiFi adapter, and connect that to the computer with the extension cable. All that is needed after that is to put the can on an old video camera tripod. Ordinary nylon ties will do for that.

Nice...looks good