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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I want to do a few small experiments that require a parabolic reflector; - solar energy - optical communications - directional microphone - wi-fi
So my ideal would be a 1m diameter astronomical telescope on a fast alt-azimuth mount but I'm wondering what I can get for a few GBP ? Obviously I can't get a cheap parabolic reflector that is suitable for everything, but does anyone know of cheap 'adaptable' options? e.g. IKEA, B&Q etc. My main requirement is that the surface reflects light, it doesn't need to be 'optical' quality.
I've looked at all sorts on eBay, solar oven metalised acrylic looks great, but I'm looking for a cheapskate option.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
FWIW I think that Wifi is probably better done with a Yagi, it's easier to get a fairly compact aerial that way with good gain and it's much less sensitive to wind and so forth.
You can build a parabolic reflector covered with aluminium foil on a hardboard backing that's cut into segments and bent into shape and mounted on a wooden frame pretty easily.
Not sure how well it would work for directional microphones, I think that might require relatively heavy materials to work well.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I am sure you have must have looked at the cheap 6" make up/shaving magnifying mirrors you can buy on ebay for a few pounds. It struck me that for optical communications you could make an array of these, rather than having one big dish, and have reduced windage to boot.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
1m2 wooden baseboard. Glue on radials cut to the appropriate quadratic curve - wood, corrugated card stuck with hotmelt glue is a wonderful roughing material, expanded polystyrene cut with a hot wire. Interpolate with hardboard or cardboard, and surface to taste - alli foil for electromagnetic, cement render for sound.
I've intended to find out how to do the sums on this one day, but have never brushed up my Bessels. Remove a circular aperture from the side of a reasonably air-tight box. Stick down a sheet of plastic, and pull enough low pressure to get a concave curve of sufficient depth. It won't be parabolic, it won't be spherical, but how close will it be to something that's useful? For small depth, it will approximate both of those very well. Capture the surface with glass fibre, or papier mache. Of course, if you do that with an aluminised plastic film, you've got a controllable focal length mirror. If you google 'space blanket', you can find where to buy a 2m x 2m square of aluminsed polyester for 84p, a company called evaQ8.
But that's all building. Scoring a dead satellite dish or two from scrap is less work.
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Parabolic Reflector
