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WiFi Triangulation
mikegroovy writes "WiFi software
tracks you down: 'Positioning technology company Ekahau has released an updated version of its software, which allows devices to be physically tracked when they are connected to an 802.11 WLAN network.' Maybe connections that are made from the street(or outside of a predefined area) could be automatically disconnected... It may spell an end to warchalking."
I hate the thought of other users being able to access my wireless connection. Even though I rarely have important files that I'm concerned about, it's nice to have some security.
The Political Programmer
Hint: War-chalking happens because people are clueless about their networks. The problem is networks that let everyone on board by default without any encryption.
"Ekahau reckons there is a market for networks used primarily for location-based purposes as opposed to carrying other data. "
Can't remember the last time I saw the word, "reckons" in a major publication. I reckon it was some time ago.
there was a article in wired about students use triangulation in 802.11b networks for all kinds of crap. since they only have a wireless lan there, professors and students write software for it because everyone uses it on their laptops and pdas
For some more info check out the company's website. Here's the page on EPE. Looks like pretty neat technology. Easy to set up and accurate to within 1 meter. I doubt warchalkers will be deterred though. :)
Karma: Excellent (In Soviet Russia, karma pimps YOU)
Not likely. The systems that get picked up by war____ers are generally the ones that someone took out of the box and plugged into the wall. Anyone who bothers to set up a triangulation system would probably already be using MAC restriction or other security measures. (Technically, you can still see a secured network and mark its location, but you could do that with a triangulation-restricted network too).
>It may spell an end to warchalking.
I thought that warchalking existed more for those who are offering wireless access to alert others than revealing the open status of another's network. Any warchalkers want to chime in? Are you guys mostly ID'ing your own WAPs or the WAPs of others?
The 802.11b network at my school fails after 50 feet.
Don't throw away that chalk just yet!
There are a lot of benefits to having this ability. At work, I can now equip our parking officers with wireless PDA's and soon I will be able to make sure that they are not sleeping in the lobby of some building instead of writing parking tickets. Maybe they will actually be out to ticket people parked illegally while attempting to warchalk from their vehicle! Now that's irony!
You should take a look at this article. Students at Dartmouth College have been using / developing wi-fi tracking systems for a while now. A nice way to track down your buddies at the campus.
One way to get around a measure like this is to obtain a surface which can reflect EM radiation at 2.4ghz, such as AMQ coated polycarbonates or crystalline-structured metallics. By using a small set of these "mirrors" at strategic locations, you could fool the software into thinking you're actually receiving from inside the CEO's office.
Since most modern triangulation techniques, including Ekahau's, depend on standard mathematical models of radius delta-reduction, it's trivial to set up your reflectors in such a way that the tracking mechanism can't deduce a logical place for your signal to originate from. Hopefully as location-spoofing becomes more commonplace, the government won't enact any laws restricting the use or registration of EM reflective surfaces.
Triangulation of EM is based on the assumption that the strength of a signal will diminish with the square of the distance from the source, or some other constant function with other signals.
When was the last time you were using wireless (especially through a wall) that had the same range from the access point in any direction?
I can't picture it working in a supermarket, with the metal shelving, compressors for the cold storage, etc. Sure, in a lab it'll work great, but with any kind of range or non-uniform building structures, not a chance.
Since a huge proportion of us who have publicly-accessible Wi-Fi networks do so by choice you have to wonder what the value of tracking users is. If people use my hub I'm okay with it as long as they're not abusing it, more power (or bandwidth) to them. I don't need to track people using my hub, if I didn't want them I would spend a few minutes reading about security and prevent people from using my hub. The only people who would need to track users would be corporations but their security departments are so damn paranoid they're barely ready to admit Ethernet may be secure, let alone cool shit like Wi-Fi.
The technology to fool technology tends to always be slightly ahead. Expect WiFi location spoofing to follow.
I used to find people by pinging their computers! I'd ping a friend's laptop (using their Windows computer name), look at their IP, then go find them on campus. I think I scared a few people when I'd say "Stay right where you are" and walk over to the study room where they were hiding.
Although I guess using triangulation accurate to a meter would let me say "You're on my spot on on the couch. When I get back from class, you gotta move."
My god, don't these people realize that everything is supposed to be free? (That's "free" as in I-should-be-free-to-take-whatever-I-want-without- paying-for-it", of course).
That's not what warchalking is about. It is about marking open access points, not about breaking into networks.
It should be legal to plug an AP into my DSL line, put a chalk mark on the side of the building and allow people nearby to use my connection for checking mail or the occational browsing.
Is it shoplifting or trespass if your neighbour put a radio in the window and you listen to it while relaxing in your yard?
Securing an AP is fairly trivial, and people who don't want the occational stranger to access their network should take the 30 seconds needed to enable WEP or password/MAC security.
If J.K.R wrote Windows: Puteulanus fenestra mortalis!
And it implies that triangulation is not involved:
So perhaps if you bump the power of your signal from the outside they will think you are inside.
www.bannination.com Two things float to the top he
I found a new open network near my girlfriends apartment,opened up my browser to /. and saw this as the lead story.
Perhaps I'd better log off now....
Where does the school board find them and why do they keep sending them to ME?
I am walking down the street right now hijacking a wireless connection and nothing is happen to...[End of Transmission]
I can think of several ways it might work, but all of them present significant challengs. Relying on relative signal level would be ludicrous, because signal level changes dramatically with card orientation, reflections, and whatever's in the middle. Heck, I get significant variance in signal level on the fixed links between the antenna on my roof and neighbor's sites.
Using a GPS-like timing comparison might do the trick, but it's set up backwards. With GPS you have a bunch of atomic clocks in orbit, and one device correlates the relative signal phase between them. With APs, you have to have extremely accurate timing across all the APs, which is a very hard problem (I've researched it...). Once you have that, you can compare reception times of a packet from the device being tracked, and triangulate. Problem is 1 meter accuracy represents some scary clock accuracy numbers across several APs with just an Ethernet between them.
If anyone can think of any other way to pull this off (WITHOUT modifying the client, and ideally without any special hardware, i.e. implementable in the HostAP driver), post them here.
GStreamer - The only way to stream!
Triangulation works great in two dimensions, but when you use a third you have to do quadrangulation (is that even a word? I'll bet it is) like say you work for a company in a five story office building, when you triangulate where a person is in relation to you distance wise and in which general direction, but you don't really know where he is, maybe he's 15 meters in front of you and maybe he's 5 meters in front of you, but three floors down. They could both register as the same with triangulation. I will start the quadrangulating WiFi revolution.
Actually, from my understanding, you draw a line from each reciver that goes off forever in the direction the signal came from. Where these lines cross, is the location where the signal was sent from. At least, this is how they use triangulation to find the source of radio transmissions when they want to find lost ships at sea (find where their last radio transmission came from, and start searching from there), or other such uses.
the current guesstimate is that sales will drop about 20% due to online copyright infringement.
Anybody who comes up with any kind of estimate is an idiot, and is obviously being "funded" by some interested party. CD sales went up when Napster was in its prime. What does that mean? Nothing. Maybe the fact that we're in a major recession and people don't have as much money to blow on stuff, or that the crap they're pushing for sale... naah, that couldn't be it. It must be those Music Pirates! Arrr!
"If he thinks he can hide and run from the United States and our allies, he's sorely mistaken." Bush on bin Laden
One way to do it is to determine the direction the signal is coming from using two known points. This is quite easy, and can be done with even basic direction finders. Imagine that point A and point B are directly east/west of each other. Now, draw a ray from point A outward at, say, 45 degrees. Draw another ray starting at point B at, say, 275 degrees. Where they meet is the location. This form requires only two points.
The other way requires three sites. You use a timing method to determine how far away they are. Imagine points A, B, and C (the location of the points is basically arbitrary, so long as they aren't too far apart). Draw a circle with a radis of one inch from point A (indicating the signal, determined by timing is, we'll say one mile away), and another with a two inche radis from point B. In most (but not all) circumstances, the circles will meet at two points. Thus, in most (but not all) circumstances, two will not be enough. Now draw a circle around C (I can't give you a radis length as I am unwilling to do the math in my head) to intersect with one of the other two intersections. If you've done it right, no matter how hard you try, assuming you've drawn perferct circles, the circle around point C will only meet with one of the two A/B circle intersections. This make any sense???
You could set the laptop up to turn off the wireless card when not in use. They only know where you are if you use their network. And it shouldn't be too hard to block pop-ups on you own laptop/handheld that weren't associated with a webpage request on you end.
However, while this won't add much to the most secure systems, it would allow companies to reduce the hassle associated with maintaining a reasonably secure wireless system. For example, a company like Starbucks might want to offer internet access to customers inside the store, but keep people from using it in the unaffiliated bookstore next door. Or, a company might want to offer internet access to visiting consultants, customers, etc. without dealing with setting up each device. (Full disclosure: I have never used a wireless LAN, so I don't know how much trouble it is to connect to one that is properly secured. I would imagine it could become at least an annoyance.) If a company was willing to assume that the building was secure, they could allow access from any point withing the building. If you were paranoid, you could limit this to business hours.
Whiteboard capturing devices use a similar principle. Two microphones are at opposite ends of the whiteboard and an ulrasound emitter is attached to the pen. When you move the pen the CPU unit attached to the mikes triangulates the postion of the pen and renders the digital image of the whiteboard. I always thought it was a simple and elegant solution compared to the touch sensitive whiteboards that cost much more. Another company now has a mini version of this technology for iPaq which attaches to a normal writing pad and allows you save anything you write on your iPaq.
To buy more Wi-Fi repeaters! My wife is gonna kill me when the bills come due!
Always going forward, 'cause we can't find reverse.
I can see it now.. the BOFH getting out of a weekend at the helldesk because the Boss spent forty-five minutes in the bathroom the day before downloading pictures from nymphoasianlesbians.com. Bring on the blackmail and the lawsuits!
Even the very term "triangulation" implies that you'll need 3 access points to do it.
- With 3 access points, you can generally locate a signal rather well, because they can see more points, and in particular if the 3 APs are located in a triangular fashion, with the user in the middle, youcan quite accurately track them.
The accuracy of the system will be almost entirely dependent on the number of access points that a user can see at a given moment, the more APs, the more accurate. Just like GPS.not really, triangulation means two detectors, one working on the x axis, saying left or right is stronger, one working on the y axis saying up or down is stronger. the third point in this trangulation is the transmitter you are hunting. your explanation is correct for 3d space. where you would need a z-axis detector.
Yes, it will confuse it.
:-)
Their method will probably even fail if you switch WiFi cards. I've got a Compaq WL110 which has a range of about 10 feet. My Lucent card on the other hand sees the access point from 100 feet, without line-of-sight (I assume the radio waves bounce off the ceiling through the window; no other way to explain _that_ range).
My access point has antennas that can be moved into different polarisations, and in an off-colour configuration, access without line-of-sight becomes really spotty: it works in one place, and a few feet to the side it stops.
But it seems to me the point of the seller is not to track abusers, but rather to track known-good devices in a known area. That alone is a cool concept, if you see what contortions people go through now when designing warehouse positioning systems. I've seen the results of an automated fork lift running through the wall of a warehouse because the reflective pad that marked the end of the aisle was covered in grime.
Hmmmm, I can envision the next hobby: sit outside a warehouse with a 2.4GHz klystron, wait until you hear the fork lift come down the aisle, then switch on the jammer and watch the fireworks
Bert Driehuis -- All I asked was a friggin' rotatin' chair. Throw me a bone here, people.
Microsoft Research did some work on this a couple of years ago - they called it RADAR.
The equations they use are pretty simple, and they seem to be getting very optimistic results. They, too, use signal-strength triangulation, together with a model of the local area (so you feed in how many walls are between you and the AP, for instance), and some processing based on recent history. That's to say, four out of the five latest samples have you outside on the pavement, and one of them has a 50 yards away in the eastern wing, you're probably still on the pavement.
Venkata N. Padmanabhan has some more papers on this on his homepage. Victor Bahl has a demonstration here but I guess it only works on IE.
Just use a slightly directional antenna--anything that relies on signal strength to triangulate you will end up being way off. If you set it up carefully, you can even choose your "virtual" location. And, no, the government can't really outlaw directional antennas.
TCP/IP has nothing at all to do with this, nor Zipf's law, nor any inverse square law, nor any kind of physical model. The system simply builds an empirical numerical model relating received power at the access points to location. As long as received power varies reproducibly with distance (not even necessarily monotonically) and you get enough independent measurements, that is possible.
If the system used triangulation, you would be right. But it doesn't. All that is required is that relative signal strengths are reasonably reproducible for each location and that you have enough measurements to distinguish all locations you are interested in. The system internally produces a map of which combinations of signal strengths correspond to which locations. To reduce the number of calibration points you need, you can try use interpolation between nearby measurements, which will usually work reasonably well/
Not the best option if you want security... Triangulation requires 3 WAPs in distinctly different spots. Most home users don't have a WAP in their kitchen, bedroom, and bathroom. It may be argued that universities have WAPs all over the campus. That may be so, but is a wardriver usually in the range of 3? I am no expert on campus WAP placement, but the only places I immagine could be triangulated would be roughly the center of the campus. So while multiple gradebooks are being accessed by a host with an unknown MAC address, the triangulation software will say "Not enough base stations to determine location".
That also depends on your beam shape. If one uses an antenna that receives a very narrow beam but has a lobe at 180 degrees in addition to one at 0 degrees (and is steerable), you'll be able to trianglulate easily on the signal unless the signal originates at or near a point between the two antennas. The error elipse would be rather elongated at that point. If the source was at 45 degrees relative to both antennas, your error elipse would be small and you'd have an accurate fix on their location.
When calculating position on range alone, two antenna sites will indeed result in two intersection points, but that's not really trianulation anyway.
Don't anthropomorphize computers, they don't like it.
actually u need three.
go test it out.
get a compass and two points 4 inches apart. if u know a user is 3 inches from one point and 2.5 inches from another point there would be two possible locations the user could be.
you need three points.
u only have signal strength(which is prop to distance) not angles. so you need three points to clarify any point in two dimensions. And four or more to more acurately place a point in 3 dimensions.
its like gps'es
http://www.howstuffworks.com/gps1.htm
The research group I work in used many of the same techquies that this software company uses to create Nibble which also can do positioning using Wifi; http://mmsl.cs.ucla.edu/nibble/. Free. GPL'd source is available too.
Things to note, however, about any 802.11 tracking software it that its accuracy is poor > 5 meters, unless you are using 5 or 6 *simultaneously* accessible access points (it even states this in the Ekahau manual). Tracking software can be thrown off by even seemingly minor enviornmental changes like crowds of people etc. Also some calibration is also required.
Don't worry about this shutting down free access points as it is way harder to do location tracking than it is to set up an encryption system (even really good VPN style encrytion) or a simple MAC address filter.
Mike
Rather than using signal strength for triangulation, you use it to record a "radio map", and compare your current position to the map. The basic steps are:
1) Walk around a room, recording the signal strength to each AP (so you get a file such as "Access Point #1, Avg signal: 96 AP#2, Avg signal: 74 ..."
). Netstumbler or other software can help you make this file.
Create a "profile" like this for every location you wish to map (roughly, one every square foot or meter). The number of profiles determines the granularity of the system, but too many profiles can cause "collisions" in the sense that different locations have similar profiles, for some reason or another. There are ways to combat this, one of which is to make an educated guess on the new location based on the last one. (i.e., the user could not have walked over 10m in one interval)
2) When a user connects, they can compare their current signal strength info ( such as AP#1, signal: 34 AP#2, signal: 74) to the map: the closest point is probably their location.
I did a simple euclidean distance calculation (taking each profile as a vector in some large space [cool how the pythagorean thm. generalizes, eh?]. There are many better ways, which I am researching this semester, but euclidean distance is fine for now.
I'm pretty sure this is why they must spend an hour per 10,000 square feet to "calibrate" the system. I had to do the same, but it was a *lot* slower; I need to make a tool to do this automagically.
This semester I am also looking to get my system working with an ipaq robot running familiar. It's the combination of the palm pilot robot kit and this positioning system. Hopefully, the little robot should know (roughly) where it is, and be able to be controlled via the internet.
Check out my webpage if you are interested in more details.
Odds are about 100% that if you are setting up multiple wifi base stations, you are placing them for optimal coverage of your own intended users. Wifi triangulation works best when the user is somewhere within the perimiter of the base stations, and works most poorly when the strongest received signal is a station on the perimiter.
So to accurately determine if someone is outside the intended coverage area, wouldn't you really need to deploy additional base stations? For instance, if you have three stations at your business, one near the front, and two in the rear corners of your building, and someone is wifi'ing in from the bus stop bench outside, he's going to hit the front station and not do much for the two in back. It's very hard to tell this user apart from someone just inside the building and very near the front base station. To settle this, you'd need a base station like across the street or something.
I don't see wifi triangulation as a practical way of identifying users outside the perimiter for this reason.
It's also worth noting that it would be a poor choice to place the base station right at the front of the building, because you'd be wasting 50% of the station's coverage area. But to pull the stations in toward the building's center would further degrade your triangulation abilities because relative signal strength differences would lower your triangulation precision.
Just tossing ideas out, I'd propose the best way to keep warchalkers out if that is your intention, is to deploy your base stations in such a way as to not provide (effective) coverage to areas outside your premisis. If your business is already too small to keep coverage just inside your building, then obviously buying several base stations to try for triangulation is patently absurd.
Of course, my final suggestion would be to openly allow public access, and use it as a P.R. booster. Free advertisement is handy, and in most cases, this would almost be free.
For the entrepeneur: I haven't seen anyone selling warchalking plaques yet. I bet there are some businesses out there (cafe's etc) that would buy a custom made brass or bronze wall plaque they could affix to the outside of their buildings to attract more customers.
I work for the Department of Redundancy Department.
Unless someone can point out a flaw in my logic.
The effect may be far too small to use in practice, though.
You're right, you need four, but this isn't why, and the math is ugly. You can't tell how far away a signal is from a given point, unless it's broadcasting with known constant strength or sending a time signal or something like that. What you can tell (sometimes) is how far away the signal is from router A, compared to router B. You might have a ratio of distances, or a difference of distances, either of which pinpoints location on a hyperboloid. This surface is two-dimensional, and for every reference you add, you strip off one dimension, so you need two more references. After that, the solution will be unique with high probability, as long as your references are not coplanar. The math, requiring simultaneous quadratics, is not pretty.
If you could tell the exact distance to the signal from each access point, you could probably place 3 of them cleverly to give you a good location. For example, if the access points were on the top floor, you take the solution below them, unless you believe the person accessing your network to be warskydriving.
I hereby place the above post in the public domain.
I'm not sure this "party line" of "check your network often for rogue APs" is all that sensible of a solution.
I'm not saying there's anything wrong with doing it, if you so choose. I just feel like it's playing "whack a mole" with a technology that network admins would be better off dealing with "head-on".
If a given environment requires a high level of security from people outside the building gaining network access, they should make efforts to block the radiation of the wi-fi signal beyond their perimeter. A farraday cage of sorts could be constructed to shield the signals from getting out. This might make a lot of sense in the construction of new bank buildings, for example. (Just place wire mesh behind the drywall that goes up against outer walls.)
For those unwilling to go this far to solve the problem, it still seems like good network practices should "save the day". Let's say, for example, war-driver X does find your sale guy's new, unsecured access point, and gets on your corporate LAN. How is he/she any different from a visitor who decided to plug his laptop into an available network port when he sits down in one of your company's conference rooms for a meeting?
In both cases, you'd assume the person wouldn't be able to do much more than get issued a valid IP address and be able to "ping" stuff. He/she doesn't have a username or password, so therefore, no security granted to modify or open any resources. (Or is your network lacking security on important files and/or directories, so all users get default access? If so, *there* is your primary issue!)
Even if your only concern is that war-driver X not be able to bum free Internet access off of you - that's solvable too. If you set up a front-end that requires authentication before using the web (or ftp), you can stop that. Of course, your employees might resist the inconvenience of having to "log in again" to use the net each time.... but hey, you should really be logging what sites they're visiting anyway if you're concerned about security and legal liability.
"Warchalking means exposing unsecure Networks. "
Bollocks it does! I'm fed up hearing this negative view of warchalking coming from people who don't have a clue. I have a warchalk symbol outside my house to denote that I give free net access, not that I have 'an insecure network.' Warchalking is about telling others what is available, and it doesn't imply that the network is insecure or illegal in any way.
No wonder warchalking is getting so much bad press these days. Next I'll be having the Police at my door, arresting me for being a hacker on my own network and telling others about the free net access I've found.
Bloody idiots.
/me dials...
You raise some good points, but Joe Salesman plugging in an AP - even if it's already strictly against policy - will usually be a big problem.
If conference rooms are set up to allow outsiders, then if you're sane (and you were able to get your bosses to cough up the money, admittedly), it's set up in a DMZ of it's own, unlike the internal networks.
Now, I set up my DHCP in a paranoid fashion - if I don't know the MAC, it doesn't get an address... but that's often not workable for bigger places, and if the WAP-adder has enough technical savvy, he may realize he needs to make his WAP pretend to be his old box by MAC, and get on that way. If the WAP is handing out it's own addresses to those that connect by it, now you can't MAC filter anymore.
And once the person's on the inside LAN, a little bit of arpflooding (which, admittedly, your IDS should be picking up, but folks often don't have them internally because of the false alarms all the time) will make the switches failover and start acting like hubs - and he can sniff away at traffic to get passwords.
In essence, I view it not as re-checking for AP's specifically, but just another part of the constant check and recheck of your setups that you need to do to see if something has been changed in a way to break access controls that exist. HIDS, NIDS, tripwire, etc all factor in to this, making sure you haven't opened up a new vulnerability is just part of the big picture. It won't make you safe in and of itself, but neither should it be ignored based on trust that the rest is all "strong enough".
Remember this? They used an ultrasonic echo-location system to build a spatial "mouse" which could be used to turn posters on walls into "smart posters" (click here to turn the lights on and off, etc.) and also to track users within their lab, so that your phone calls are forwarded to the phone nearest you, etc. At the time, I thought, how redundant... they need ultrasound for tracking and an RF system of some sort to transmit "clicks". Why not just use a wireless network and come up with a triangulation method to find the location of the WiFi device using its own emissions. Well now it's been done. So it should be possible to use a PDA with a WiFi card as that magic 3D mouse thing. Imagine having location-relevant UIs for things: as you walk down a hall you get light-switch controls on your screen for nearby rooms, a map, the meeting schedule for the nearby conference room, reminders about stuff you need to do while you are in this area of the building, instant-messaging informs your colleagues that you are nearby, etc.
Of course for smart-poster purposes, the resolution ought to be better (1 meter isn't good enough) but perhaps that could be improved.
I think in the future location tracking will usually have 2 tiers: outside you use GPS, and inside buildings you use radio-triangulation of some kind. It will be a sort of standard eventually. Because you need higher resolution indoors, for various reasons. And since buildings don't move, the building triangulation system can tell you precisely where the building's "origin" is in lat/long space, so you would still be using GPS-style coordinates, just with greater accuracy in indoor situations. Instead of being deprived due to the fact that GPS signals don't penetrate well enough, you actually get better quality.
Anybody else tired of security always being in the limelight? Yes we need that kind of geek very much, but fundamentally their job is a lot more boring than what's going on in the research labs... And these security "mine's bigger than yours" wars are getting almost as annoying as the MS hate-fest, or the Apple hate-fest of a decade ago.
http://www.kismetwireless.net/
While it wouldn't be implemented on the AP itself, 3-4 cheapo PCs with WLAN cards could easily be set up as packet sniffers that would show signal strength of all clients in the area.
http://www.instant802.com/ (I think) - AP with open firmware.
retrorocket.o not found, launch anyway?
Well, I see you've already been modded down.
Good.
Except for the smallest of businesses, more than 1 AP is needed.
My building has at least 4. (Using Cisco LEAP - Our admins aren't stupid.) I believe one in each end (north/south) on each floor. I would classify ourselve as medium/small. (2-floor building, not that large. There are MANY office buildings in this area that are MUCH larger)
retrorocket.o not found, launch anyway?
The Mattel Power Glove also worked this way
retrorocket.o not found, launch anyway?
Big problem with your system - The Pringles antenna
Using an antenna like this will make your position fix dependent on not only the client's position but on its orientation too.
I suggest trying an omnidirectional antenna of some sort. (http://www.aerialix.com/ has cheap kits based on the Guerrilla.net designes)
retrorocket.o not found, launch anyway?
Cards can be calibrated as well.
/. is a geek site?).
Uh-huh. I agree. But I think I pointed out that if you control the client PC cards, you have an entirely different situation than the big brotherish scenarios where unwilling users were to be traced, that started this whole thread.
I recently made a tour of a mountain side, and according to my GPS wound up 100 meters higher than the top. To my recollection, I had at least one foot in solid contact with the mountain at any time. I checked the GPS's reported EPE and the difference between its datum and MSL, but neither could explain that difference. Signal reflection could.
My IEEE 802.11b card has an external aerial that I can orient for maximum interference (and of course, I've been toying with that to explore the interactions with my adjustable base station antenna, weren't you warned that
Bert Driehuis -- All I asked was a friggin' rotatin' chair. Throw me a bone here, people.