Kismet, antenna diversity, receiver preamp

[mrmeebles]

I was reading the posts regarding someone's new rig. 3 different antenna. And the question of whether an amp or receiver preamp helps with Kismet.

I am running Kismet with a 200 mW Ubiquiti card. I have the 7 db mag mount antenna from Comet. I also have a prism 2.5 card with 2 ext antenna that I was using previously. I also have a 10 dbi omni that I would like to use.

I know that it's important not to use 2 antenna of different types to send and receive data. I thought if using kismet nothing is sent so two antenna of various types would not be a problem. I had hoped to be able to use 2 antenna of different strengths for the different coverage areas (the flatter larger higher db doughnut and the more spherical lower dbi reception area).
Question 1: Is this completely unfeasible?

Pseudo-multi part question 2 how should I best invest my money: should I get an amp (or receiver preamp), should I get a pcmcia to usb adapter to run a second card or should I get a second mag mount 7 dbi comet antenna to match the one I have now? :

Question 3: I had thought the direct correlation between transmission and reception ability (there's a name for this that I can't think of) would imply that an amp would help with kismet. Of course, it does seem a little counter intuitive. Will an amp (or receiver preamp) really help kismet?

I thank you in advance for forgiving my scathing ignorance.

[mrmeebles]

ccie4526
PostPosted: 03 Jul 2003 02:21

Food for thought....

If you're running kismet or similar passive sniffer software which doesn't do active probing (a la netsumbler), you can use an MMDS receive preamplifier between your antenna and network card.

[/size]

I apologize for invalid assumptions; I thought if an August 2006 post (and nothing after) was debating Kismet and amps that the question had not been answered or that the answer wasn't readily available. well that was silly.

So, if I mounted 3 24dbi parabolic antenna to the top of my car with amps on all of them, would I be legal? Of course, the next question is could I cover them with fiberglass without too much signal loss? Or should I have them inside the car? Which I guess wouldn't irradiate me, right?

[mrmeebles]

I've decided the next steps towards wireless betterment for me are:
1. get a mini pci card with a prism chipset and mod my laptop so I'll have an n-male or female sticking out. Of course, I'm a little nervous about popping open the laptop.

2. get an orinoco usb stick with external antenna jack.

Then I will have an Atheros (my ubiquiti pci-mcia), a prism (which I really love), and an orinoco.

3. After that I'll work on getting the amp (receiver pre-amp).
4. I'll work on getting better antennas.

[argh]

receive gain is everything with Kismet. if you are using multiple cards in Kismet, you can change the config file to intelligently use the multiple cards. you can have one card stay on channel 6, and the other(s) scan all the rest of the channels, or scan all the channels split up among the extra card(s).

if you have antenna with differing gain all running under the same Kismet instance, the weaker ones will simply miss things. if antenna A has 8 db of gain and is scanning channels 6-11 and antenna B has 2 db of gain and is scanning 1-5 you won't see much on 1-5 by comparison.

if you had multiple instances of Kismet running on separate devices as drones and reporting to a central Kismet server, differing antennae could work better. such a setup is extreme in a vehicle, but people do it.

a good receive preamp would indeed help. a cheap one may give you more noise as well. getting your gain from an antenna is usually best. exceptions exist; like in a long run of coax putting your amp at the antenna can help a lot.

a 24db parabolic with receive preamps will be completely legal. at least until you transmit. you could have it inside a vehicle safely as long as you never transmit on it. it will also have a pattern focused very tightly, and unless you are trying to reach something distant while stationary will not work well as the main antenna for wardriving. an antenna like this will typically have a left/right beamwidth of 10 degrees! that's a pretty skinny slice. it will typically have a vertical beamwidth of 8 degrees!

such an antenna would work better for wardriving pointed straight ahead or behind.

a moderate gain omni usually will work the best, for all around wardriving.

[mrmeebles]

you can have one card stay on channel 6, and the other(s) scan all the rest of the channels, or scan all the channels split up among the extra card(s).

Would it be worth setting the atheros on six, use the prism to scan the other channels and sweeping the horizon with a waveguide, yagi, or parabolic?

Currently, I own an 8db black mag mount and a 10 dbi 2' white normal omni. I have been wanting to use but it seems a little too conspicuous to mount on top of the car. I had wanted a 15 dbi omni but at 6' seemed very conspicuous. Could I paint it black? would that interfere with reception?

if you had multiple instances of Kismet running on separate devices as drones and reporting to a central Kismet server, differing antennae could work better. such a setup is extreme in a vehicle, but people do it.

Ohhh. This leads me into something I had been pondering a while. Would I want to use a wrt54g as the server (or a similarly modded open wrt router)?

I have an atheros pcmcia. I don't have the mini pci or usb card. I'm actually a little worried about modding the laptop to put in the u.fl cable to a n male mounted on the case. I could use my pcmcia atheros for channel 6, an orinoco usb with external antenna jack to scan, and maybe connect two panel mount antennas to the wrt. Do people use multiple wrt54g's in a vehicle?


I know hratch has a desktop with 11 cards with 11 omnis. But where does the absurdity become more than the gain? Okay, I see that cards for 1 , 6 , and 11 could help a lot, but after that?

Last edited by mrmeebles on Sat Feb 24, 2007 2:38 am, edited 1 time in total.

[mrmeebles]

a good receive preamp would indeed help. a cheap one may give you more noise as well. getting your gain from an antenna is usually best. exceptions exist; like in a long run of coax putting your amp at the antenna can help a lot..

Having the amp next to the antenna seems like it might be difficult with a mag mount. Having it next to the computer wouldn't help? ahh. I think I see the logic. The coax is five feet of low loss and I've been meaning to trim it, but I thought my trimming and craftsmanship would cause more loss than a factory assembled connection with low loss. I don't suppose you could recommend an amp. I was thinking about one from hyperlink. Of course, I trust fab-corp a lot. I was thinking of one with a usb power supply.

a 24db parabolic with receive preamps will be completely legal. at least until you transmit. main antenna for wardriving. an antenna like this will typically have a left/right beamwidth of 10 degrees! that's a pretty skinny slice. it will typically have a vertical beamwidth of 8 degrees!

Oh. I thought I had read of a (cisco) antenna with 120 degree horizontal beam width. I knew the vertical was pretty meager but given the distance I thought the reach would more than compensate.

a moderate gain omni usually will work the best, for all around wardriving.

I thought that might be the case with a 7 or 8 db omni so that it could have distance but the radiation pattern (doughnut) wouldn't be too flat.

Thank you for your help.

[argh]

sorry so long in following up...

Having the amp next to the antenna seems like it might be difficult with a mag mount.

by a long run, i meant something more along the lines of an external antenna mounted above your roof at home. for the feedline lenghs involved with a vehicle, it wouldn't make much difference, assuming quality feedline.

The coax is five feet of low loss and I've been meaning to trim it, but I thought my trimming and craftsmanship would cause more loss than a factory assembled connection with low loss.

i wouldn't worry about five feet, if it is low-loss coax. you are correct in avoiding cutting it yourself. unless you are comfortable soldering N connectors, you could wind up losing a lot (or most) of your signal. it won't damage anything, since it's receive-only. better to just buy a shorter jumper.

Oh. I thought I had read of a (cisco) antenna with 120 degree horizontal beam width.

120 degree beamwidth are likely to be sector antennas. you mentioned a 24 db dish, and it's gain will typically be more than a sector, and it's beamwidth tighter.

[mrmeebles]

Thank you for the reply.
I decide to go with a 400 mw mini pci card. Originally, I had considered getting a prism, but the ones I found were type IIIa and I needed type three B. So instead I got an Atheros. It says 400 mw but the few tries I made weren't impressive. Of course, that could be from loss from the u.fl to n male pigtail, but that seems doubtful. Also, it's a pain running two atheros at the same time.

Could you please recommend a receiver preamp?
Thanks again.

[argh]

i do not yet have an Atheros chipset card, but i desire to greatly. the possiblities of controlling the radio completely in software are very interesting to me.

i cannot recommend a receive preamp for 2.4 ghz, as i have no experience here.

[mrmeebles]

I have only begun to look at madwifi. However, it grew on me fast. The wlanconfig options (and the other options) that come with the atheros chipset cards are great. Thanks again.

[i_do_dew]

Could you please recommend a receiver preamp?
Thanks again.

I know this is old, but I didnt notice it at the time. Do a search for posts by WrzWaldo. he runs a preamp. after you read all the posts then ask him a question that isnt in the FAQ

[Petzl]

I use a diamond MG-200 antenna mounted on a 14db pre-amp .... and then i have 5 meters coax to my card, with the 14db extra gain i have no problems with the lengt of my cable.

Place you preamp directly under your antenna ....

[mrmeebles]

I know that the pre amp needs to go next to the antenna. I'm just trying to imagine how this will work with my Comet antenna on a mag mount. The mag mount itself has the coax connected to it; I certainly don't feel comfortable enough soldering to work the preamp into the line and the idea of the preamp between the antenna and mag mount seems a bit funny.

I have seen the blue Fab-corp preamp recommended several times; it would be nice to see (a picture) of it in an actual (mobile not on a roof) setup.

[whitedice]

I know that the pre amp needs to go next to the antenna. I'm just trying to imagine how this will work with my Comet antenna on a mag mount. The mag mount itself has the coax connected to it; I certainly don't feel comfortable enough soldering to work the preamp into the line and the idea of the preamp between the antenna and mag mount seems a bit funny.

I have seen the blue Fab-corp preamp recommended several times; it would be nice to see (a picture) of it in an actual (mobile not on a roof) setup.

Pic from How to get 300K+ points in 9 months (rig pics)

[mrmeebles]

Thank you for your picture. The preamps aren't as close to the antennas as I had thought. I am curious about what preamps look like with mag-mounts.
But I guess it doesn't matter much...

by a long run, i meant something more along the lines of an external antenna mounted above your roof at home. for the feedline lenghs involved with a vehicle, it wouldn't make much difference, assuming quality feedline.