Intro:

    A friend of mine and I were talking about how he planned on rolling out some wireless access points in his house. We decided that he should use two access points on opposite sides of the house. Then he said “But how do I keep the neighbors from seeing my signal?” That got the old hamster in my head running on his wheel.


A question:

    “How can they snoop if they can’t even get a signal?” Thus the quest began. How to stop a wireless signal? The first thing that popped into my head was the lead vest that x-ray techs use on you at the dentist. I decided that was too obtrusive, and possibly expensive. I then thought about a steel plate, but that presented the same problems. A salad bowl…nope. Then I remembered an episode of the Discovery Channel’s Myth Busters. They made a cage out of insect screen to create an area devoid of rogue radio frequencies.


Doing it:

    I ran down to the local hardware store and picked up a roll of said insect screen. This is the same material you use on your screen door; at least we do here in the south. I then picked up a Kensington Wi-Fi detector…not because I wanted to, but because I NEEDED to…hehehe.

(1) Survival gear for a laptop ranger	(2) Da screen

(3) Da screen II

    I placed the Wi-Fi detector about six to eight feet from my access point and turned it on. The meter showed full signal strength. I then took my screen and cut a piece about one foot by two feet. I then wrapped the screen around the Wi-Fi tester and hit the button. What do you know…it worked! Time to build the access point screen…

(5) Full strength	(6) Dead signal

    This ain’t rocket science! I took my already cut piece and folded it on itself so that I have about a foot square piece of screen. My access point just happens to be the same size as a NIC box I had laying around. I roughed in the size leaving about an inch extra overhang on the sides. I then folded the ends over about a quarter inch and smoothed out the ends with a screwdriver handle. A little fold here, a fold there and ta-daa!

(7) Folded corner	(8) 3 sides folded

(9) NIC box	(10) Folds clean - keeps shape well

    The front of my router faces the neighbor’s house, so this is the side I chose to measure signal on. I placed my meter about 4 – 6 feet in front of the router and the signal had degraded by one light. This degradation was just enough to kill the signal by the time it left my house’s outer wall. If you need to cut down the signal more, just keep adding layers of screen.

(13) Router B4	(11) With screen	(12) No signal outside of house

    The actual cost of this project was about $.50. It was either keep the neighbors out of my network, or get a Dr. Pepper…decisions, decisions :). Nothing makes me feel good like a ghetto mod. :) If my laziness wasn’t such a concern, I could have formed the mesh directly on the access point and on the antennas themselves. As a side note the cone made from a Pepsi can gets me enough gain to cover the entire house. So much for soup cans and formulas for placing antenna wires…hehehe.


Closing:

    If you enjoyed the read or attempt this yourself, drop by the forums or drop me a line. We love to see our projects in use.

Update 02/06/05:

    A reader did contact Greg for some help and insight. Below is a sort of transcript of sorts. So there you go, some extra information...


  Drew:

    Sorry to take so long to get back to you, but I’ve been quite busy.

    If you wish, please include this as an update for your website, only please don’t offer my email address as I’m not an expert in this field and am only performing an experiment. I don’t think that my insight would be that extensive if people have questions.

    As an experiment I am trying to make a room devoid of Wi-Fi signals so that the neighbors access points or cards do not interfere with my throughput rates. Considering that the special wall paper made by a British weapons contractor costs $100 dollars per square foot, I needed to look for something less expensive.

    Enter Greg's article on blocking Wi-Fi signals from his access point so the neighbors can’t ride his waves.

    I started by downloading NetStumbler 0.4.0 and reviewing how strong the neighbors’ signals were. Walking around there were about 12 signals coming in if memory serves me. I also chose an internal room instead of a room with windows as radio signals penetrate windows better than walls. I went to the local Lowe’s Home Improvement store and picked up a roll of aluminum screening that one would use to re-screen your patio door if your kid runs through it. Using a staple gun I started at the top of the wall and ran around the top of the room, leaving the door uncovered. The door is solid oak by the way. This single layer considerably weakened the signal strength under the “Signal” column, not the “Signal+” column. But the signals were still getting in. So I moved down the wall and making sure to overlap the two pieces I ran another ring around the room, again leaving the door uncovered. I now had half of all my walls covered in aluminum screening wallpaper. This did not accomplish as much as I had hoped. Not keeping the as many signals out as I’d like I continued down the wall to the floor. Again this didn’t have as much success as hoped. I then contacted Greg and he suggested grounding the wire meshing, this was done by using an extra power cord from a computer cutting the sheathing off the wire and exposing the green wire. I then cut the FLAT prongs off of the plug and left the round grounding plug. I plugged it into an electric socket and stapled it to the screening. This had a negligible effect but it will keep me safe is an electric charge runs through the screening somehow. Since we have a drop ceiling attaching screening to the ceiling proved difficult, we ended up using Duck tape and drywall screws that are sunk into the tiles. This killed 75% of the signals. I then put up a second layer on the walls and there were still two access points getting through. Finally I covered the door in two layers of the screening and those two access points disappeared.

    Now here is the problem. I have two access points outside the “Clean Room” and I still see them, but I control them so I’m not concerned by them. That also means that people can see my internal access point. For what I needed done this is a success. But if someone is trying this as a security means then I would recommend more layers of the screening. At which point the room starts to look really dreary and it’s going to start getting costly depending on the room. I didn’t need to make my room completely clean so I’m not going that far so I’m not sure if it’s actually possible but I do know that when I walk into the room my Cingular cell phone loses network connection. Verizon is the only company to penetrate in.

    The access points that penetrate into the room are about 20 feet away and 50 feet away. So their signal is very strong whereas my neighbors are an unknown distance away. This is a large determining factor in the wire screening’s success. Take that into consideration before you ruin your den.

  Greg:

    One thing that I have yet to test with the setup is how well it will work if you were to ground the mesh. I don’t really recall where I ran across this, but I remember thinking I should give it a try. As far as your question about the ceiling, that may be a source of the rogue signals. The Wi-Fi’s radio waves can be bouncing their way in! I would like to see you grounding the mesh first though. If this works for you, and with your permission, I would like to update my article with your results. I hope I could be of some help!

  Drew:

    I am attempting an experiment where I’m trying to keep outside Wi-Fi signals out of a room while keeping the inside signals in the room and usable. I’ve purchased wire meshing and have installed it one layer thick around almost the entire room from floor to ceiling. Not including the floor or the ceiling. But I still have 3 rouge access points broadcasting through, and my access point does not “stay up” in that my reading on NetStumbler goes up and down intermittently. So I’m assuming that the wire meshing isn’t thick enough (not enough layers) to keep out outside access points and is to thick because it’s gobbling up my access points’ signal. That’s just an assumption. Is this possible? Could the rouge AP’s be coming in through the unprotected floor and the ceiling? Do I need to increase the amount of wire mesh on the walls?

    Any insight you could provide would be very helpful.

  GREG:

    Doors allow signal, and another layer would more than likely be helpful. Some signals can manage to “bounce” through the ceiling.

Editors Note:

    So there you have it folks. ~ David







 

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