Even as recently as mid these were uncommon in the United States, though they have been around for years in Europe. In most health food supermarkets you can also find non-dairy milk substitutes rice milk, soy milk, oat milk, etc. Use a sharp knife or single-edged razor blade. A dull knife will mostly just deform the cardboard and put you in danger of getting yourself sliced up.

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Even as recently as mid these were uncommon in the United States, though they have been around for years in Europe. In most health food supermarkets you can also find non-dairy milk substitutes rice milk, soy milk, oat milk, etc. Use a sharp knife or single-edged razor blade. A dull knife will mostly just deform the cardboard and put you in danger of getting yourself sliced up.

Whatever you use, be careful. The necessary materials are these: A Tetra Brik of a suitable size. More on this below. About 2 inches of 12 or 14 copper wire. A silver-plated type N male coaxial connector, chassis that is, 4-hole mount.

Four next nuts for the above screws. Eight "spiny" lockwashers see photo at right of a suitable size for the above screws. These, by the way, are very important! Optional A handle or bracket of some kind. What this turns out to be depends on how you intend to use the antenna. A round needle file with a sharp point ground on its tip is also useful for making screw holes in the cardboard Brik. A small soldering iron, and a scrap of electrical solder. A small screwdriver and nut driver for the size of the hex nuts that you use.

The handle is optional; some people in keeping with the kitchen-trash nature of the project just use duct tape. Step 1. Get Yourself a Brik! Above are three common products packaged in Tetra Brik containers.

They are 65 X 95 X millimeters. The Tetra Brik container as opposed to the soup is a European product, hence the metric measurements. At right I show the logo at the bottom of the carton. Look for it. Make the soup for lunch I recommend adding some Egg-n-Onion Matzo! Use a fine-point permanent marker like a Sharpie to put lines on the Brik for cutting or hole-poking.

Step 2. Tip: cut about an eighth of an inch down from the top of the box. For the cleanest cut, draw good straight lines in Sharpie marker on the brik where you intend to cut, and follow the lines with the knife or razor blade. Besides, the worse it smells, the more likely it is that your dog will haul it off into a corner and shred it for you.

Step 3. The size of the Brik is critical to calculating the correct feed point. What works for one size will work less well or perhaps not at all for a different size. You must measure the Brik and calculate a feed point dimension for that particular Brik. The guide wavelength calculation depends on the first two calculations, so they must be done in order as explained below.

Note that the calculations are best done using metric units, because the speed of light is very close to ,, meters per second. The free space wavelength depends only on the microwave frequency at which Wi-Fi operates. For Wi-Fi channel 6, the frequency is 2. Free-space wavelength can easily be calculated by dividing the speed of light in millions of meters per second by the frequency, in millions of cycles Hertz per second. Because both values are numbers of millions, the "millions" cancels out, and you can use a formula like this to calculate the free-space wavelength in meters: This yields.

Channel 6 is the center of the Wi-Fi band in the US. If you calculate your antenna for Channel 6 it should actually work fairly well all across the band.

On the other hand, if you want to calculate a value for one of the two ends of the band, use the frequencies of MHz for Channel 1, or MHz for Channel The value, however, must be plugged into the next calculation. This is a little more involved, and is a function of the frequency and the geometry of the waveguide.

In other words, rather than use Ditto cutoff wavelength. The result value will also be in meters. Plug the values into the equation to see if you come out with the same answer! Step 4. Mark the Feed Point and Make the Hole The feed point is positioned along a line down the center of the front face of the Brik. There is a seam down the center of the back face which will make mounting the N connector difficult.

I recommend drawing a line down the length of the front face, at the center, as shown in the photo. Measure your feed point offset value from the bottom of the Brik along the center line of the front face. In the photo at left, I stuck a white self-adhesive address label to the Brik so that the mark indicating the feed point would not be lost amidst the details of that vegetable medley, heh.

This is the diameter of the coaxial N connector flange that must pass through the wall of the Brik. At this point, set the Brik aside. We need to make the probe assembly. Step 5. Make the Probe Assembly The probe consists of a male N coaxial connector with a short length of 12 or 14 copper wire soldered into its "solder pot.

Nickel-plated N connectors can be had for less, but they may not be "microwave-friendly" due to lossy insulation material. Go for silver. Be suspicious of anything with yellow or non-white insulation around the solder pot. Some older and cheaper N connectors use phenolic insulation, which is lossy at microwave frequencies. Find a piece of 12 copper wire about 2" long. Remove any insulation. Straighten the piece of wire as completely as you can.

If it solders crooked, re-melt the solder and straighten it. The touchiest measurement in the whole Tetra Brik antenna project is the length of the wire in the probe assembly.

The length is the free-space wavelength divided by four. For Channel 6, that would be Now, the idea here is to do your best. Admittedly, measuring a fraction of a millimeter is a dicey business, and although the closer you come, the more sensitive your antenna will be on Channel 6.

One end, obviously, is the tip of the wire probe. The other end of the measurement is to the level of the white Teflon insulation that surrounds the solder pot of the N connector. Step 6. Center the N connector body on the line you drew on the Brik. Take a marker and mark the four mounting holes onto the Brik, as shown at left. Placing a mailing label on the Brik as I show here helps to make the marked points more visible. An awl will work, and some jackknives have something trekkers call a drill, which is really a type of awl.

I use a round needle file with a sharp point ground on the tip. Using a needle file allows you to make a crisp, clean hole by poking the file through the cardboard and then filing the holes to a diameter that will pass the mounting screws. After drilling or poking the four mounting holes, take a razor blade and trim away any cardboard protruding from the holes into the Brik.

This next step is probably the trickiest part of the project, aside from measuring the probe length. The four screws that mount the probe assembly to the Brik must contact the foil.

This is not easy! The way I found works best is to use eight spiny lock washers. When you tighten down the hex nuts, use a nut driver and push them hard. You must tighten the hex nuts sufficiently hard so that they force the lock washer spines through the thin plastic film covering the foil, allowing the washers to make electrical contact with the foil. Test it with an ohmmeter after tightening the four hex nuts: Touch the N connector body with one probe, and force the tip of the other probe through the plastic film layer to contact the foil liner.

Tighten the hex nuts a little more and test for continuity again. If necessary, carefully abrade away the plastic film over the four mounting holes with the finest sandpaper you can find. Note: Make sure your test probes are sharp enough at their tips to pierce the plastic film layer to the foil beneath. If necessary, file or bench-grind at least one one needle-sharp.

Step 7. What sort of thing you mount it to depends on how you intend to use it. It can be used as a "bandwidth expander" to bring a Wi-Fi marginal connection up to full bit rate. I detail how this situation occurred to me in my book in Chapter


Jeff Duntemann's Drive-By Wi-Fi Guide

A PowerPoint slide show on the topic is here. Atheros rocks! Cisco is buying Linksys! As usual, only time will tell.


Jeff Duntemann s Drive-By Wi-Fi Guide






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