A Cardboard Horn for 802.11b

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Fun. Well, it doesn't stand the rain yet, but it is easy to build and gives you a lot of dB.

The waveguide that feeds the horn is the bottom of a Tetra Brik (see MicroTVAerial). The horn is made of cardboard covered inside with kitchen aluminium foil.

http://users.skynet.be/chricat/antennes/cornet0001.jpg http://users.skynet.be/chricat/antennes/cornet0002.jpg http://users.skynet.be/chricat/antennes/cornet0003.jpg http://users.skynet.be/chricat/antennes/cornet0004.jpg http://users.skynet.be/chricat/antennes/cornet0005.jpg

The images are still in Belgium... maybe a local copy would be faster

The box is 42x25x25 cm (16-1/2 x 9-7/8 x 9-7/8 in.). The horn's aperture is about 25x25 cm². The Tetra Brik bottom is about 8.5 cm (3-11/32 in.) long (the ~3 cm (1-1/8 in.) rod is at about the middle). Four pieces of cardboard covered with aluminium foil make the horn. They are about 32 cm (12-9/16 in.) long. Their big side is 25 cm (to match the box side), and the small sides match the milk box (6.5 cm and 9.5 cm, or 2-1/2 and 3-3/4 in.). You can find some theory in "The W1GHZ Online Microwave Antenna Book".

...And the results speak for themselves :)

http://users.skynet.be/chricat/antennes/bighorn.png

Of course, maybe it would be better to use something other than cardboard, but it was so easy. I seem to get 12 dB more (!) than with a Ricore can (diameter ~10 cm or 3-15/16 in.). When one knows that with 6 dB one gets double the gain, here I multiply the distance by four (with one horn). With two Ricore cans, we made more than 5 kilometers, Liege 2002.04.01; sorry, it is in French, so...

15 Jun 2002, we tested two of these horns at 9.5 km (~6 mi.), Liege2002.06.15 (in French). One horn with various antennae:

Here are the results:

http://users.skynet.be/chricat/horn/retinne.png

Note that the noise figure is unusually high (usually, it is around -100 dBm). In this British horn, he choose a cut-off frequency of 2 GHz with a waveguide internal dimension 76 x 38mm (3 x 1-1/2 in.) to reject 1800 MHz cell phones. It would be interesting to see if it helps.

Here are the 'principles' of a horn design:

http://users.skynet.be/chricat/antennes/horn-drawing-150.png

There is also a Cardboard Horn Antenna Designer (beta version?).

Of course, when you have space, you can build a bigger one.


See also


The Ricore can is based on the saunalahti.fi antenna2.

http://users.skynet.be/chricat/antennes/ricore.jpg

ReseauCitoyen.be BoiteDeConserve1, in French.

--xof (Liege, Belgium 02 Jun. 2002)

CardboardHorn (last edited 2008-04-13 16:36:02 by localhost)