Wifi transmitter locator

You can usually get a clue from the SSID (name) of the wireless "source". However, if it's non-descript, the only other alternative is to do some direction finding. This is not easy, takes some practice, but works fairly well.

The basic trick is to have:

1. Wi-Fi card with an external antenna and that is fairly well shielded. I use a PCMCIA card with aluminum foil wrapped around the PCMCIA antenna.
2. External directional antenna. I use a 19dBi dish antenna. This has a -3dB beamwidth of about 15 degrees which is good enough for direction finding. Other antennas will work but make sure they have a narrow beamwidth.
3. Software that will display signal strength. This can be part of the driver that came with the wireless card, stand alone application, or Netstumbler.

There are many tricks to doing direction finding. Just fumbling around looking for the strongest signal is a guaranteed failure. You will be fooled by reflections and obstructions. What I do is use a map. I locate myself and take a bearing. With the bearing, I draw a line on the map from my location. I then move to another location and draw another line. Do this often enough, over a long baseline, and the majority of the lines will cross one point on the map. There will be some lines going off in random directions. Just ignore those. This works especially well while moving in a vehicle.

There is also software that will do this automatically.

Good luck.

Thanks. This is way beyond what I can do!! But it helps to know

Well, then let me suggest a way that you can do it with just your laptop.

1. Figure out where the antennas are located on your laptop. If you have two antennas inside your laptop, open the cover to the the wireless MiniPCI card and disconnect *ONE* of the antennas. The antenna will probably be somewhere in the LCD part of the laptop, on the right or left side, near the top. There are often photos on the laptop manufacturers web site showing the antenna location. If you have a fancy microwave oven leakage detector, you can sometime locate the antenna by starting a big file transfer and looking for a signal. It will be VERY weak, but the oven leakage detector should find it.
2. When you have located the antenna, put a big sheet of aluminum foil over the antenna on the side facing the display. Hold it in place with Scotch tape. Wrap the foil around the edge. You can add additional aluminum foil on the back of the laptop if necessary, but don't cover the antenna area. The idea is to leave a narrow slit, approximately the width of the antenna (1/4") on the back of the laptop, directly over the antenna. This will make the antenna very directional.
3. You will need to do a boresight alignment. There is no guarantee that the antenna is pointed exactly perpendicular to the laptop case. Find a nearby access point and use the signal strength indicator to determine the direction of maximum signal. That's where the antenna is pointed.
4. The rest was explained in my previous posting. Use a map. Draw lines in the direction the antenna points. Move around. Where most of the lines cross, is the transmitter. Since your laptop can "see" the mystery access point, Netstumbler should work for signal strength and identification.