Fun with a parabolic reflector

[glitch]

So I came up with an extra satellite reflector. Being a generally curious fellow I wondered if I could use it with my Wardriving rig. My standard set up is a CF-19 Mk1, usb Wifi with external antenna that has a magnetic mount, and Pharos 500 gpsr.

First I modified the mount for the dish, I cut the post and mounted it to a piece of plywood. In the picture its setting on an old birdbath. I wanted it low to fit in the back of my SUV. Normally I slap the antenna on the roof, its magnetic mount is good to at least 70 mph.

I reasoned that it would increase sensitivity and signal. The parabolic would give me a good direction information. I assumed, ya'll know what that means...

So I set it up and tested it on my home network. This is what I have found out so far.

I cant use the secondary reflector shown in the photo, finally resorting to holding the external in different positions I found the focal point. It was no where near where you would think or calculate.
After measuring the dish its a near perfect parabolic shape. With the secondary reflector I thought they had distorted the parabolic to reflect the waves to secondary. The design probably has a high loss the way they use it.

With no parabolic I got -59 dBm. With both parabolas I got -59 dBm.

With the main parabolic I got -55 dBm. And that was very directional! Super pinpoint directional. Useless for Wardriving directional.

So I assumed I would be able catch the networks that were farther away. So much for assuming... My search for a better antenna will continue. I will still play with this one too.

Note: The source was over 120 ft away, inside my house, a net gear low powered router. The internal card got -80 dBm at the same distance. I forget Signal quality numbers.

So ideas? Comments?

Edit. I am going to edit the photo so it fits better.

[Shawn]

What photos..?

[glitch]

It was to big, you caught me adjusting it. It should show up now.

[kode-niner]

I presume you're only doing the 2.4Ghz bands. Have you calculated the distance between that antennae and the dish to match the wavelength so that it bounces at the zero-crossing point?

Also that omni antennae loses efficiency with the length of the cable. I've had good success with high-powered Alfa USB wifi with high-dBi antennas attached with short pigtail adapters.

[Springfield]

You might try a USB wifi receiver and mount it at the focal point. Then run a good quality USB cable from the receiver to the laptop. No signal loss. Also, some of those "parabolic" dishes are strongly off-axis so the focal point is way off to the side -- yours looks that way in the picture.

[glitch]

Part of the setup that is not shown in the photo is a USB TP-Link TL-WN722N WiFi unit with an external removable antenna. I then got a TP-Link TL-AN2408C 8 db antenna with a magnetic mount. That antenna is what I am focusing the parabolic dish on.

I have never played with parabolic antennas. Looking at this one I thought it was a "distorted" parabole to focus the waves down and toward the second reflector. The transceiver mounted between the to posts. So I took it off and bolted a metal plate that the magnetic base would adhere to and I could slide the TP-Link antenna back and forth to find the sweet spot.

However, after playing with the setup I actually measured the dish. It is slightly oval shaped from the front view, but its parabolic shape is the same from top to bottom and then side to side. Also it was designed for microwave transmission. The focal point is about 24-30 inches dead center of the dish as far as I can tell.

When it cools off tonight I was going to play with it some more.

On a side note, I looked at the CF-28 board but did not find a good wifi card mentioned. What would anybody here suggest if they had to buy one? I can use the Tp-Link but would like a good internal card to keep the usb free.

[Springfield]

You missed my point. Put the actual USB receiver at the focal point, not just an antenna. That way you don't have any coax loss from antenna to receiver, rather a strong digital data line on a USB cable into the PC.

[glitch]

No, I understood, but this was going in the back of my suv and I don't have the cords to stretch that far right now, I just forgot to tell you that part. Sorry.

You are entirely correct that the antenna mounted right on the usb dongle would cut losses.

My communication skills are almost as bad as my social skills...

Now that I have started this experiment I am looking a yagi antennas. I think they may be what I want, semi directional with good (11-20 dB)
gain. That lead to biquad antennas, but I digress.

[Springfield]

On a side note, I looked at the CF-28 board but did not find a good wifi card mentioned. What would anybody here suggest if they had to buy one? I can use the Tp-Link but would like a good internal card to keep the usb free.

EnGenius EMP-8602+S is miniPCI with 600 mW output and great sensitivity. Designed for a wifi router but works great in CF-28 and CF-29 Toughbooks.

No, I understood, but this was going in the back of my suv and I don't have the cords to stretch that far right now, I just forgot to tell you that part. Sorry.

You can find an "active" USB cable with built-in hub for 15 foot lengths or more. Less than 15' a good quality passive USB cable should work.