Hardware Hacking Projects for Geeks

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Part I: Basic Hacks, Tools, and Techniques

802.11b/g and 802.11a

Radio Frequencies

The 802.11b and 802.11g wireless net-

work cards operate at a frequency of

approximately 2.4 GHz. This antenna

was designed with that frequency in

mind. 802.11a operates at 5.8 GHz; if

you shrink the can assembly parts by

50%, it should work at that frequency.

Project Overview

This project uses the Lucent Orinoco 802.11b card, but any brand of

802.11b network card will do. Whichever design you choose to build, you’ll

need a “pigtail” connector that has the proprietary Lucent connector (for

the PCMCIA card) on one end and an N connector on the other. The pigtail

can be obtained from a number of online stores for $35 to $40.

You’ll also need to know the basics of soldering for this project. The con-

struction of either range-extending antenna for your wireless LAN card can

be completed in a few simple steps.

WARNING

Before attempting either of these hacks, you need to be aware of the FCC

regulations on maximum allowed power output from an antenna at the

frequencies that the 802.11b cards operate. Read FCC part 15.247 at http://www.

access.gpo.gov/nara/cfr/waisidx_00/47cfr15_00.html.

Hardware Assembly Instructions for

Recycled Can 802.11b Antenna

This hack is quick and can be very useful. I put together a can-based

antenna in about two hours. I then took it to a local café that offers a pay

802.11b service. After powering up my laptop and connecting the antenna,

I slowly moved the antenna around, scanning for other networks. Within

one minute, I had located another network and “borrowed” access instead

of having to use the pay service.

If you are interested in using these antennas at other radio frequencies, the

dimensions can be scaled appropriately.

It is quite simple to take an ordinary metal can and transform it into a

directional antenna for your 802.11b network card in four simple steps. See

Exhibit A for a complete list of materials you’ll need.

Project Overview

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Chapter 3, How to Hack 802.11b Antennas

1. Select and prepare the can

Locate a metal food can that is between 3 inches and 3.25

inches in diameter. A longer can is better. Be sure the can

is clean and dry, and that the open end is free from any

ragged metal edges.

2. Measure and punch holes in the can

Drill a hole approximately 2.5” from the closed end of the

can for the N connector. You can find this connector from

DigiKey, Radio Shack, and ham radio stores. Depending

on where you buy it, the exact dimensions may be differ-

ent from those shown in Figure 3-1, so check the dimen-

sions of your connector. Also drill several smaller holes

for the mounting screws. Figure 3-1 shows where the

connector will be mounted on the can.

3. Build and install the antenna probe

Next, take the N connector (see Figure 3-2) and add a

short piece of 12-gauge wire so that the wire sticks up

1.21” above the edge of the connector.

Mount the N connector to the hole you drilled in the

previous step. Figure 3-3 shows a cut-away view of the

completed antenna. On the left you can see the N con-

nector with added wire “stub.” Hold the N connector in

place with four 4-40 screws and nuts.

4. Add a connection cable and test

The radio signal from your 802.11b wireless card must

now be connected to the antenna. The Lucent Orinoco

PCMCIA card has a tiny (and proprietary) connector at

the end of the card. A small plastic cap usually covers this

connector. Remove the cap.

You will now need to either locate an adapter connector

cable that changes the tiny Lucent connector to a stan-

dard N connector, or open up your PCMCIA card and

solder a wire to the antenna inside.

Figure 3-2: N connector (back and front)

Open end of canClosed end of can

2.5”

0.72” 0.64” diameter hole

‘N’ connector

mounting holes

0.125” diameter

‘N’ connector

mounting holes

0.125” diameter

Figure 3-1: Antenna connector location

Open end of canClosed end of can

2.5”

‘N’ connector

1.21”

Figure 3-3: Antenna location and length

Recycled Can Instructions

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