Wireless+Networking+in+the+Developing+World_Part8

Wireless+Networking+in+the+Developing+World_Part8 - Chapter...

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Figure 4.37: Tin the end of the wire before soldering. 5. With the soldering iron, tin the central pin of the connector. Keeping the wire vertical with the pliers, solder its tinned side in the hole of the cen- tral pin. Figure 4.38: Solder the wire to the gold cup on the N connector. 6. Insert a washer and gently screw the nut onto the connector. Trim the wire at 3.05 cm measured from the bottom part of the nut. Chapter 4: Antennas & Transmission Lines 131
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Figure 4.39: The length of the wire is critical. 7. Unscrew the nut from the connector, leaving the washer in place. Insert the connector into the hole of the can. Screw the nut on the connector from inside the can. Figure 4.40: Assemble the antenna. 8. Use the pliers or the monkey wrench to screw rmly the nut on the con- nector. You are done! 132 Chapter 4: Antennas & Transmission Lines
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Figure 4.41: Your nished cantenna. As with the other antenna designs, you should make a weatherproof enclo- sure for the antenna if you wish to use it outdoors. PVC works well for the can antenna. Insert the entire can in a large PVC tube, and seal the ends with caps and glue. You will need to drill a hole in the side of the tube to ac- commodate the N connector on the side of the can. Cantenna as dish feed As with the USB dongle parabolic, you can use the cantenna design as a feeder for signi cantly higher gain. Mount the can on the parabolic with the opening of the can pointed at the center of the dish. Use the technique de- scribed in the USB dongle antenna example (watching signal strength changes over time) to nd the optimum location of the can for the dish you are using. By using a well-built cantenna with a properly tuned parabolic, you can achieve an overall antenna gain of 30dBi or more. As the size of the para- bolic increases, so does the potential gain and directivity of the antenna. With very large parabolas, you can achieve signi cantly higher gain. For example, in 2005, a team of college students successfully established a link from Nevada to Utah in the USA. The link crossed a distance of over 200 kilometers! The wireless enthusiasts used a 3.5 meter satellite dish to establish an 802.11b link that ran at 11 Mbps, without using an ampli er. De- tails about this achievement can be found at http://www.wi -shootout.com/ Chapter 4: Antennas & Transmission Lines 133
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NEC2 NEC2 stands for Numerical Electromagnetics Code (version 2) and is a free antenna modeling package. NEC2 lets you build an antenna model in 3D, and then analyzes the antenna ± s electromagnetic response. It was de- veloped more than ten years ago and has been compiled to run on many different computer systems. NEC2 is particularly effective for analyzing wire- grid models, but also has some surface patch modeling capability.
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Wireless+Networking+in+the+Developing+World_Part8 - Chapter...

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