Antenna Test: Alfa APA-M04

The gear needed for wardriving

10 posts • Page 1 of 1

Postby bigstape » Wed Jul 31, 2013 12:10 am

I acquired two Alfa APA-M04 2.4GHz 7dBi Indoor Panel Antennas. They're small and inexpensive, about $7 each, I think. The configuration of my vehicle is such that I can easily mount them with zip-ties so they're pointing out the rear-most side windows, each feeding their own Alfa AWUS036H. BTW, the side that says "Alfa" is the hot side. Anyway, took them out on my test course, 917 APs seen. As a reference, I ran this course recently with my mainstay MobileMark IMAG5-2400 from fab-corp and saw 950 APs.

So, not too shabby.
Image

I've been outside the box. There's a bigger box.

Give a man a fish, and you feed him for a day. Teach a man to fish, and eventually you will run out of fish.

Postby henn9438 » Sat Dec 14, 2013 10:19 am

I was thinking of it as a mobile mount on my bike.

Postby bigstape » Tue Jan 07, 2014 7:45 pm

Yes, they're nice and small, you should be able to zip-tie them to the frame or something.
Image

I've been outside the box. There's a bigger box.

Give a man a fish, and you feed him for a day. Teach a man to fish, and eventually you will run out of fish.

Postby cyphonix » Sun May 18, 2014 1:29 am

It's really too bad that there isn't a mobile whip equivalent to this:

http://www.amazon.com/Alfa-Hi-Gain-Omni ... 0046CBR3W/

Postby cyphonix » Sun May 18, 2014 1:30 am

Perhaps it's time for me to quick messing around and get a copy of the ARRL antenna book. Perhaps I/we could design something, or figure out how to re-purpose a (1.2GHz?) ham antenna for 2.4GHz.

Postby bigstape » Wed May 28, 2014 2:15 am

In my research, I ran across a web page where someone built their own wifi antenna. It consisted of many small segments linked together. The problem is that it is an indoor antenna. We already have excellent indoor wifi antennas available (I like these: http://www.data-alliance.net/servlet/-s ... SMA/Detail). But they are a bit awkward for wardriving. Some sort of "whip" antenna would be nice, if it is do-able.

What I'd like in an antenna is:
1. 12dbi (or better)
2. Inconspicuous (no need to upset the muggles)
3. Mag-mount
4. Weatherproof
5. AWUS036H compatible (RP-SMA)

Note that 1 & 2 may be incompatible.
Image

I've been outside the box. There's a bigger box.

Give a man a fish, and you feed him for a day. Teach a man to fish, and eventually you will run out of fish.

Postby cyphonix » Sun Jun 01, 2014 2:20 am

I think I have a design in mind. It would be a bit costly, but.... would satisfy all of your criteria.

I'm debating whether or not to acquire the parts and build it. If I do, I will let you know what it entails.

Postby cyphonix » Mon Jun 02, 2014 5:10 pm

Ok... Here's the idea. I'm referring to this as "the CUBE".

You take a square (wooden?) box, of about 17" or so, with locking lid... I'm wondering if lining the inside of the box with foil might add a "ground plane" behind the antenna to capture multipath.

You "tile" 4 14 dB outdoor plane antennas on each side (4) of the box, in a 2x2 formation (coverage pattern is 80 deg horizontal, 30 deg vertical).
To each "side" you connect (mount on the inner sides of the box) 4 Alfa cards, a 4-port usb-hub, and a Raspberry Pi. Each "side" leaves one card on 1 one on 6, one on 11, and one to hop the remaining 2.4 G channels.
To each Pi, you connect a GlobalSat BU-353S4 GPS puck. You put the pucks on the top of the box, or sprawl them out anywhere on the roof of the vehicle.

You power the entire setup with a boatload of 5VDC current (a line from the battery with a 12-to-5VDC converter from Digikey, or 8 12000MAh New Trent Battery packs)
You affix the "cube" to the roof of your vehicle via magnets, tie-downs, ladder/luggage/bike rack or other means.

14dB in 4 80-degree "sectors"
Smaller & ambiguous antenna footprint/appearance
Mag mount
Highly effective
Quick installation/removal/start-up (remote power switch, perhaps)
Weatherproof (for each antenna cable, a small "drip loop" should probably be made, and a bit of silicone caulk should be used so that there's no water infiltration)

My current setup is the same thing, only using 7dB Radiolab antennas (1 pi, 4 cards), and is VERY effective (a cron job restarts kismet every hour on the hour to prevent file sizes that Wigle wouldn't allow. In a densely populated urban area, I've seen (1 hours worth of) file sets that contain > 11,000 unique networks, and over 90,000 AP locations in the gps file.

Yes, there would be a large degree of duplicate data between the 4 setups. Yes, this build cost would be expensive. But, it accomplishes the following:

The design above would lower any RF feed line loss (2-4dB?),
Increase antenna gain from 7 to 14dB
Create a friendlier appearance than the array of 4 mag mount antennas on my trunk
Would be the closest thing to a "catch all" rig that I can come up with

Thoughts?

Postby bigstape » Wed Jun 04, 2014 1:48 am

I would like to leave the antennas as exposed as possible. I'm already using two 12dbi antennas inside my car, "looking" through the side windows, yet the Mobile Mark 5dbi on the roof still seems more sensitive. A "whip" antenna would be ideal, but my understanding is that the whip has to be cut to some length that is a multiple of the wavelength of the frequency one desires to receive.
Image

I've been outside the box. There's a bigger box.

Give a man a fish, and you feed him for a day. Teach a man to fish, and eventually you will run out of fish.

Postby cyphonix » Wed Jun 04, 2014 8:06 am

I'm already using two 12dbi antennas inside my car, "looking" through the side windows, yet the Mobile Mark 5dbi on the roof still seems more sensitive.
That''s not surprising. Any antenna outside the car will do (potentially much) better than an antenna inside the car. There may be (at least traces of) metallic content in the automotive glass, and assuming you're car isn't non-metallic (plastic, fiberglass), the rest of the body will cause shielding and all sorts of nasty multi path within.
my understanding is that the whip has to be cut to some length that is a multiple of the wavelength of the frequency one desires to receive
That's correct. There are many, many designs. 1/4 wave, 1/2 wave, 5/8th wave, and tuned elements can be "stacked" in-phase to compound gain, or perform on multiple bands (this is why you see wound coils in the element itself, or coupled between elements on commercially available antennas.

Rather than have the "porcupine" effect (4-16 whip antennas), "the CUBE" would revert to 16 plane antennas to keep gain high, but to use an array of directional (high gain) antennas, to achieve omni-directional reception. This is done all the time. This photo shows the master FM array on Prudential tower in Boston (note the "grappling hook" looking things, each one is an FM antenna). By stacking so many elements (mind you, the placement is precise, as to remain in-phase), massive amounts of gain is achieved. Also note, that there are elements pointing in each direction (N, S, E, W) around the sides of the tower.

http://gallery.bostonradio.org/2004-05/ ... 4-med.html

Since the horizontal pattern of the 2.4Ghz plane antenna I was looking at is 80 degrees, a similar configuration will work for "the CUBE".

I'm not sure if you saw my other post, but I did analysis on the first 90,000 or SO APs I found. 97-98% of them were on channels 1, 6 or 11. Since I've reconfigured my current setup to "lock" 3 cards, 1 each on 1, 6 and 11, with the fourth card hopping among channels 2, 3, 4, 5, 7, 8, 9, 10, 12, 13 and 14, I've noticed that I'm picking up many more networks (and geometrically more AP/position combinations in Kismet's .gpsxml file) based on my file sizes and number of unique networks per file set.

10 posts • Page 1 of 1

Return to “Net Hugging Hardware and Software”

Who is online

Users browsing this forum: Google [Bot] and 1 guest