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QUESTIONS AND ANSWERS
 
Question 621

A friend was telling me of a guy who created a TV satellite dish out of chicken wire in his attic — how would you do it, adjust it, and what kind of home-brew receiver would be required to use it? - BP
Since the microwaves used in satellite transmissions have wavelengths of several centimeters or more, they can't pass through holes in a conducting material if those holes are less than about a centimeter in diameter. As a result, chicken wire reflects microwaves as though it were a sheet of solid metal. You can form a dish antenna by bending chicken wire into a parabola. When the microwaves from the satellite strike this parabolic reflecting surface, they are brought together to a focus at a particular point above the center of the parabola. If you then place a microwave receiving device at this focal point, you'll be able to watch satellite TV.

If you want to do this, you should make a cardboard template for the parabolic shape and bend the chicken wire carefully to match this template. The more highly curved the parabola, the closer the focus will be to the dish's surface. You should aim this dish directly at the satellite and put the receiving unit at the focus of the parabola, above its center. However, you'll have difficulty building the receiving device yourself, although there are probably kits you can buy. The receiver should have a tiny antenna, a microwave amplifier, and a frequency down-converter, all together on a single circuit board. Working with microwave-frequency electronics is difficult because the wave character of the electric signals is painfully obvious in those circuits. Designing microwave circuits is a job for experts. In short, you can build the dish, but you should buy the receiver that sits at the center of the dish.

         

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