Hardware Hacking Projects for Geeks

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Chapter 3, How to Hack 802.11b Antennas

Hardware Assembly Instructions for

Primestar Dish 802.11b Antenna

The Primestar antenna hack described here is the brainchild of Rob Frohne,

who details some of the steps at http://www.wwc.edu/~frohro/Airport/

Primestar/Primestar.html.

First, a little background. Primestar (a satellite TV company) was recently

purchased by DirecTV (another satellite TV company), which is phasing out

all the Primestar equipment. This means the dishes are being abandoned

and are available for other uses such as the one described here. If you can’t

locate a Primestar dish, you may be able to use a DirecTV or other satellite

TV system dish antenna. A little experimenting will be required to get them

to work. Primestar antennas can be found at tag sales, local newspaper clas-

sifieds, or on the Internet.

It is easy to transform a surplus Primestar dish into a highly directional

antenna for the very popular IEEE 802.11 wireless networking. The result-

ing antenna has about 22 db of gain (this means that the signal is amplified

in one direction about 128 times) and is fed with 50-Ohm coaxial cable.

Usually LMR400 or 9913 low-loss cable is used if the source is more than a

few feet from the antenna. (See the sidebar on low-loss cable.)

The resulting range of your wireless system using two of these antennas

with a line-of-sight path should be close to 10 miles at full bandwidth. I

must stress the line-of-sight path, though. Leaves and trees weaken the

signal significantly, so you will want to make sure that the path between

antennas is clear. Even rain and fog can limit the range.

The long-range link you will create can connect remote

homes to the Internet or allow retrieval of audio/video

data from remote locations. Imagine being able to set

up a web camera on the side of a mountain to monitor

wildlife or connect to a hard-to-reach local network with

full bandwidth.

In the following easy steps, you will construct and set up

a highly directional antenna. See Exhibit B for a complete

list of materials for this project.

Your resulting hacked dish should look something like

Figure 3-5. You can see the can antenna at the bottom of

the figure.

Low-Loss Coaxial Cable

Low-loss cable can be expensive

and stiff, making it hard to install

and work with. A cable with reason-

ably low loss for a decent price

is the LMR-400 cable from Times

Microwave Systems (http://www.

timesmicrowave.com). The company

has information on distributors. If you

buy this cable, it will not have any

connectors on the ends; you will have

to add them yourself. This will require

you to purchase the male termination

connectors and solder them in place.

You may also want to purchase a few

female-female adapters to make sure

that everything connects together.

Ham Radio Outlet also carries these

parts (http://www.hro.com).

Figure 3-5: Mounted dish antenna

Primestar Dish Instructions

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