How To Make: CHEAP Homemade Parabolic Reflector Antenna

[-=Xploitz=-]

A parabolic is highly directional, right?

Not really "HIGHLY directional". A cantenna is HIGHLY directional. But a parabolic has a wider spread vice the cantenna. And, with a parabolic reflector..you get TRUE gain in receiving and broadcasting. Where as a cantenna or other antenna supplement will only give you higher broadcasting ability. But with the parabolic....as far as you can pickup a signal is about as far as you can receive. So in other words...if you can pick up the AP...you can communicate with it without restriction...USUALLY.

So, if i were to use this as a defensive mechanism, i.e. attach it to an antenna with a flexible wire between the parabolic and my card that allowed me to determine the direction of someone connected to my network, what program would allow for fast sampling so that i could find the direction of the purpose in a few minutes?

Hell..you could use airodump......The higher the power reading of the connected MAC thats attached to your network...the closer you are to the person on your network.

[fds42]

Ah, i'll have to look into the .cap file format and use it for parsing. Either that or pipe the airodump output to a program that can parse it and track the locations of all users.

By the way, do you have a copy of the images on the first page? The freeantenas.com site seems to be down and it would be nice to have those for future reference.

I'm currently toying with a 3 antenna type monitoring system, where two use monopole antennas for a power reading to determine proximity and a nice set of square root functions to figure out where the signal is originating from in reference to the antennas and a middle antenna to determine directionality.

What i have in mind for the directionality one is a monopole antenna with a big metal sheet/half-box blocking signals from one direction. The purpose of the blocking is that if the signal is strong(er) in relation to the average of the two detectors, then its on the side that isn't blocked off. If its weaker, than its on the other side.

However, the problems with such a system are far too many to make in a practical sense.

Issues faced by such a system:
Varying power outputs from cards, i.e. an atheros may not output the same power level as a d-link or a wireless chipset may not broadcast as much power on battery mode as during plugged in mode.

a +5db gain antenna attachment will skew the location coordinates for something that detects based on power levels alone.

A cantenna may be able to bypass this completely and appear to be sitting right next to the AP.

The other idea i'm toying is more complex as it may involve a sweeping parabolic or a set of them and use the angle of peak power level to determine the point (two intersecting lines = person).

But this runs into problems of servos or stepper motors with interference and timing, the time based (angle ~ amount of time into sweep/period) angle detection is a problem as packets aren't sent at a uniform rate.

Who knows, if i ever went for a masters, this could probably serve as a thesis in electrical engineering - communications.

[balding_parrot]

Simple signal triangulation then.

DF loop, triangulation and foxhunt (and I don't mean the animal type) may be good keywords to look for.

[fds42]

I had considered a circular loop (referred to as a DF loop when used for direction finding) as a normalized gain is -2 to 2 db, but the problem lies in the fact that most circular loops don't work well beyond 1ghz. Not nearly high enough to act as wifi antennas to feed airodump-ng or kismet. Monopoles/Dipoles work well with just about any frequency you want to throw at them, and if you turn them sideways, they have very very similar radiation patterns to the DF loop.

The only other one that might serve the same purpose is a biconical with a polarizer (normalized -3 to 1 dB). Downside? Way more than i wanted to do. Ever come up with your own polarization mesh? not fun.

I wonder if i could take a pringle's cantenna, split it so that its less directional on a vertical slice and use it as a sort of sonar/radar sweep.

[balding_parrot]

It is obvious to me, that we could have a very long discussion on this subject, not that I intend to. The only problem would be that everyone else would be bored to tears by it, and only about four or five people here would understand a word of it. I doubt very many people would know what circular log paper looked like, let alone what a diagram on some would mean.

[-=Xploitz=-]

I doubt very many people would know what circular log paper looked like, let alone what a diagram on some would mean.

Whayt dud u sae?? Someth'n bout uh sir-q-lar dye'n-grahm? And uh sir-q-leer logg payper view thinggie?? Thats jest 2 mutch theire brane pouwher wast'd try'n 2 sae thum theire wurds.

Hell...I think I just spent 5 minutes trying to type that nonsense. I think I actually lost an IQ point or 2 just stooping to that level!!

[balding_parrot]

Whayt dud u sae?? Someth'n bout uh sir-q-lar dye'n-grahm? And uh sir-q-leer logg payper view thinggie?? Thats jest 2 mutch theire brane pouwher wast'd try'n 2 sae thum theire wurds.

QED

I think that's all I need to say on that.

[.cAkEnOoB.]

Damn im so eager to try it! ill do it NOW and post results tomorrow!

err..but one question. Do i hav to do it both at the AP and USB adapter or just the usb adapter? (wardriving?)

[-=Xploitz=-]

You can do either.

If on both...you'll see much greater gains. Just make sure their pointed at each other as best as possible for maximum gains and further distance. Much better than the 40 dollar "Cantenna"...and this cost you what?? .less than 5 bucks at home depot??

[bitza]

And, with a parabolic reflector..you get TRUE gain in receiving and broadcasting. Where as a cantenna or other antenna supplement will only give you higher broadcasting ability.

Sorry to say I do not agree with that statement! There is no such thing as "receiving gain" and "broadcasting gain", there is only one type of gain: "antenna gain", which is proportional to an antenna directivity (both in horizontal and vertical plane) and size (in case of the parabolic). The gain of an antenna works both ways, and I challenge you to find a official and scientifically approved document to show me the contrary! You also say parabolic antennas are not as directional as a cantenna, which is true when you use ready made parabolic reflectors with a focal point which is set extremely far away, but you can perfectly make a parabolic with a shorter focus point by working on it's curve. it's like lenses, in a way...
Also, a a home made cantenna can be built for $10 or less, not $40...