On Tue, Mar 25, 2008 at 11:11 AM, Ralph Shumaker <[EMAIL PROTECTED]> wrote:
> Karl Cunningham wrote: > > On 3/24/2008 3:28 PM, James G. Sack (jim) wrote: > >> Mark Schoonover wrote: > >>> On Mon, Mar 24, 2008 at 2:37 PM, James G. Sack (jim) > >>> <[EMAIL PROTECTED]> > >>> wrote: > >>> > >>>> Tracy R Reed wrote: > >>>>> Neil Schneider wrote: > >>>>>> Mark Schoonover wrote: > >>>>>> Some dude did a war flight - similar to a wardrive > >>>>>>> - in a small plane over San Diego and logged in the thousands. > That > >>>>>>> was a > >>>>>>> few years ago. > >>>>>> That would be our own Tracy Reed. > >>>>> Indeed it would! > >>>>> > >>>>> I have been considering reprising this experiment. If anyone has the > >>>>> equipment and wants to put together a proper scientific experiment > >>>>> and > >>>>> do something unique (triangulate the actual location of the AP, > >>>>> acquire > >>>>> useful data about the network involved, etc) I would be willing to > >>>>> give > >>>>> it another go. We could even fly the same path as before and > >>>>> compare the > >>>>> data. > >>>>> > >>>> I wonder what kind of antenna you would want/need for this? > >>>> > >>> I don't know. I've done direction finding work before, but only from > >>> a fixed > >>> location. DFing from a plane would be very challenging to say the > >>> least... > >>> Normally you'd use some kind of Adcock array for VHF or UHF, but not > >>> sure in > >>> the microwave bands. > >>> > >>> There is some info tho: > >>> > http://www.scitechpublishing.com/index.asp?PageAction=VIEWPROD&ProdID=158 > >>> > >>> > >> > >> Wouldn't a ordinary omni with hopefully not too thick (and not too > thin) > >> a donut pattern do the job, even? Have to have readings from 2 > reception > >> points, of course (plus altitude). Assuming a flat earth makes it > >> easier, too. ;-) > >> > >> Seems like a lot of things need to be done at once, though: > >> pick a channel > >> pick a source > >> try to quickly maximize the source signal > >> and record direction and altitude > >> do fast enough to be able to sample all channels, see strong signals > >> > >> Are there programs to help with this? Hardware? > > > > Could have a script that does continuous iwlist scanning. My > > recollection is that a scan takes a second or two to complete, but I > > don't know if that varies with number of APs found. Record the MAC > > address and signal strength for all APs seen during each scan, along > > with GPS coordinates (NMEA-183 text from serial port of GPS). Fly a > > parallel search pattern. Then (challenge here) post-process to > > correlate data and put positions to MAC addresses. > > > > When an AP is seen on more than one search leg, you should be able to > > determine a location based on signal strength in those legs. Where an > > AP is seen only on one leg, you can't do as well. > > > > Could be tested by flying patterns over (or driving by) one's own or > > other known APs. Could possibly 'normalize' the antenna pattern of the > > receiver. > > > > This ignores the radiation pattern of AP's antennas, but I dunno what > > you could do about that in any case. > > > > Karl > > > > > > A single point receiver has no depth perception, like having only one > eye open. > > Having two eyes open increases depth perception and the further apart > the eyes are, the farther depth can be perceived. > > Affixed to the plane, this would mean two receivers at either nose and > tail, or even better, at either wing tip. I have no idea how this could > be done safely. > > But you could get a *much* larger span if one of the antennae could be > "dragged" behind the airplane like one of those banners that's usually > much bigger than the plane and following way behind. > > For triangulation, perhaps 3 (each wing tip and a drag-behind) could be > used simultaneously. > > A GPS device would allow instantaneous position information for the > aircraft itself. That and direction of travel with triangulation would > allow you to fairly well pinpoint the WAPs on the ground (or elsewhere). > > How did the military triangulate enemy radio signals in WWII? (when > their equipment was far more primitive than even what the CB home user > has today) > > > > -- > Ralph > I don't know how the military DFed microwave signals. I worked down in Imperial Beach in the lat eighties, but we did high frequency DF. That's what the big antenna is down by the beach. From what I know, it's not in use anymore. That system worked by looking at the phase of the signal as it crossed all the antennas, and could provide a bearing. Many of these sites used to be located all over the world, and we could triangulate to get an approximate location. A quarter wave antenna on 2.4 Ghz is approx 31.25 mm, the antennas wouldn't have to be too far apart to work... -- Mark Schoonover, CMDBA http://www.linkedin.com/in/markschoonover http://marksitblog.blogspot.com [EMAIL PROTECTED] -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
