Tuesday, July 9, 2019

Aluminium foil in radio and antenna projects

It's common, it's cheap and there's probably a long roll of it in your kitchen. Aluminium foil. Thin and conductive, it's been used for various electronic applications. 

50 or 60 years ago, when metal chassis were both desirable and expensive, those building valve (tube) projects, especially if using battery valves, sometimes formed chassis from wooden packing crates with foil glued on. 

Foils much wider than wire can be useful. A large piece could be taped to a window to form wideband dipoles for VHF or UHF amateur bands. These can either be horizontally or vertically polarised. 

Homebrew transmitters sometimes require a shielded case or shielding between stages to remove feedback. Foil stuck onto plastic or cardboard could form lightweight boxes or partitions. 

Foil can form a ground plane for UHF and microwave vertical antenna projects. 

Here is a project describing an aluminium foil based fractal antenna

Finally, my video below shows foil being used as a variable capacitor. That could be handy for a crystal set project. 

What radio-related things have you done with aluminium foil? Please leave your comments below. 

PS: Enjoy these well-reviewed books on various amateur radio topics. They're available for under $US 5 each in electronic form. Or you can get them in paperback. Visit VK3YE Radio Books to find out more. 

1 comment:

  1. I have a Roberts portable radio dating from about 1989. It has 'twitchy' tuning, just when I think I have it tuned to a particular station on FM, I move my hand away and the static comes back. So, body capacitance has an influence.
    I tried to model a human body as a circuit by making a foil and cardboard capacitor (foil stuck to both sides of a square piece of card about 32 x 32 cm). I added a relatively high value resistor wired across the capacitor. If I put this on the radio after tuning and then step back I get no static. So my 'device' emulates a human body's additional capacitance.
    I measured the capacitor at about 1700 pF but with 89% VLoss. It made little difference whether the resistor was 100 kOhm or 220 kOhm.


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