How to build a 2.4 GHz can antenna
WiFi Signal Strength
Does your apartment do not accept Wi-Fi?
A soldering iron and a can of coffee
The author of this antenna was able to connect to the free "wi-fayu" of the hotel, located more than 400 meters from the house
How to build a 2.4 GHz can antenna
Suitable for 802.11b wireless networks and probably for other applications running at this frequency.
What you need:
1) a tin can
2) N-socket ("mother") and a pair of cogs
3) A piece of 2mm copper wire
First, you will need canning, from under paint, coffee, etc. bank. Naturally, empty and clean inside. The diameter of the can should be within 7.5 cm - 10 cm, according to calculations, the most optimal size is approximately 9.2 - 9.3 cm (banks with a half of this diameter were successfully used, I myself have not tried it myself). The height of the can should be more than 13.5 cm, but good results can give both lower and, of course, higher cans.
The can, or at least the bottom of the jar, should be made of flat tin, not wavy. I also tried a wavy, optimally short jar , the result was just as good and even better than with a jar of absolutely flat tin. So you can freely experiment with different banks.
However, it does not make sense to cut off the top edge of the jar, as I did . Of course you will get more or less even edges, but without the bearing part of the bank it will easily fall apart on the seam.
I bought myself an N-socket in Tevalo, however, they can be found in other similar stores. N-nests are mainly of two types: fixed with screws and such that have their own nut of attachment. It does not matter which of the nests to take, I bought a variant with screws (worth about 40 kroons). If the cable that comes out of your wireless network card has any other contact on the end, then you will need a corresponding socket.
The diameter of the wire should be approximately 2 mm, length about 3.1 cm. I obtained this segment from the cable left after electrical work, removing the insulation from it. Some sources advise using a 4 mm wire. I have not tried it myself, so I can not advise.
Cut a straight piece from the copper wire about 3.1 cm long and solder it to the center pin of the N-socket, holding the wire as straight as possible. Watch carefully so that the central contact with the side is not accidentally closed. The waveguide, or the same piece of wire, after fixing it on the inner surface of the can, should be above this surface by 3.07 = ~ 3.1 cm. The exact length you get already having secured the nest to the bank and having measured. The more accurate the dimensions, the better the result and the stronger the signal.
Enter your data and calculate
Now calculate the appropriate distance from the waveguide (piece of wire) to the bottom of the can by the diameter of its can. For this distance is well suited? the wavelength of the conductor. This distance means the distance from the inner wall of the can, and not from where the wall of the can end. It is also necessary to accurately drill a hole, as well. from the correct distance depends on how the waves will interfere and, accordingly, how the signal will amplify or weaken. The more accurate the dimensions, the better the result and the stronger the signal. The waves are reflected from the inner walls of the can and therefore, when looking for the right place, it should be borne in mind that the bottom of the can is higher than the end of the wall. Then you should drill a hole in the right place to properly fix the socket. If necessary, drill the holes for the fastening screws. If you do not have a drill at your fingertips, you can use a nail and file. Now it remains to fix on the wall of the can of the N-socket with soldered to it a piece of wire. It does not hurt to clean the paint in the place of attachment, which will improve the contact of the socket with the jar. The antenna is ready, you can connect the cable and start testing.
The strength of the signal largely depends on the direction, so it is necessary to guide the antenna accurately. I, for example, direct so that I first set it in the horizontal direction, and then gently move in the vertical direction. It is necessary to direct almost the same as the barrel of a gun; directly in the direction of the goal. But sometimes it also happens that the connection is best when the direction of the antenna is not exactly the same as the direction to the aiming point. You just need to try.
Aha ... to protect against the radiation of inanimate and living nature, it is necessary to close something with the open end of the antenna. For example, a suitable plastic lid that allows microwaves to pass through. The lid is suitable or not, it can be checked in the microwave oven, since it operates at similar frequencies. Place the test cover in a microwave oven with a glass of water (since an empty or almost empty oven can not be turned on), turn on for 1-2 minutes, until water boils. And if you find that the lid has heated up with the water, then this material is not suitable for closing the antenna opening, because he does not miss microwaves.
To remove condensation, you can make a small hole in the bottom of the antenna. This should prevent rapid rusting of the antenna.
In general, rust weakens the signal, and cans rust for a long time do not resist. So if the connection begins to deteriorate and the direction (aiming) of the antenna, etc. no longer helps, then it's worth to go to the store for a new can.
Also, each signal or each meter of cable connecting the antenna and the network card attenuates the signal. My approximately 10 meter cable attenuates the signal for at least a couple of decibels. So, the fewer things, the better.
Used Buffalo AirStation WLI-PCM-L11G card, at a frequency of 2425 MHz. Access point is on the mast , at a distance of about 1-1.5 km. The best stable signal that I received, directing my bank exactly, was this:
- Link Quality: 13/92 (connection quality)
- Signal level: -85 dBm (signal level)
- Noise level: -98 dBm (noise level)
For comparison, the previous "antenna", which was a sticking piece of wire behind which was a piece of tin, showed the following maximum results:
- Link Quality: 6/92 (connection quality)
- Signal level: -91 dBm (signal strength)
- Noise level: -98 dBm (noise level)
Strengthening the signal by 3 db means improving the signal almost twice, in my case this is a fourfold difference. Link Quality at about 6-9 allows the data to move already at a speed of ~ 150-250 kb / s, so at 13 there would already be a pretty good speed.
By the address
My antenna cost me about 45 CZK, because I already had a piece of wire and a bank. The search for banks and the construction of the antenna was spent about 2 hours. Here, time was not taken into account in the manufacture of fasteners for cans. The cost of a new commercial antenna would probably be four-digit.
The bank with the best signal (canned pineapple d = 9.9 cm l = 11.5cm) - but with wavy bottom and walls and shorter than ideal - it did not work because it was holed during the samples in several places.
The Mast is at a distance of 1-1.5 km.
(c) Asko Tamm 2002