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How to build a canned antenna at 2.4 GHz

WiFi signal booster

Is Wi-Fi poorly received in your apartment?

Only a soldering iron and coffee can

The author of this antenna was able to connect to the free “Wi-Fi” of the hotel, located more than 400 meters from the house.

Усилитель сигнала WiFi

How to build a canned antenna at 2.4 GHz

Suitable for wireless networks (wireless) according to the 802.11b standard and, probably, for other applications running on this frequency.

Как построить баночную антенну на 2,4 GHz

What you need:

1) tin can

2) N-socket ("mother") and a pair of screws

3) 2mm length of copper wire

TIN

Как построить баночную антенну на 2,4 GHz

First, you need a tin, from under the paint, coffee, etc. bank. Naturally empty and clean inside. The diameter of the jar should be within 7.5 cm - 10 cm, according to calculations, the most optimal size is about 9.2 - 9.3 cm (jars with a half of this diameter were used successfully, I did not try it myself). The height of the can should be more than 13.5 cm, but both lower and, of course, higher canned antennas can give good results.

The can, or at least the bottom of the can, must be made of a flat plate, not wavy. I also tried a wavy, optimally short can , the result was just as good and even better than with a can of absolutely smooth tin. So you can freely experiment with different banks.

However, it does not make sense to cut off the top edge of the can, since I did it . Of course, you will get more or less smooth edges, but without the carrying part of the bank it will easily fall apart along the seam.

N-nest

Как построить баночную антенну на 2,4 GHz

I bought myself an N-nest in Tevalo, however, they can be found in other similar stores. N-jacks are mainly of two types: fastened with screws and those that have their own fastening nut. It makes no difference which nest to take, I bought a version with screws (cost about 40 CZK). If the cable that comes out of your wireless network card has some other contact at the end, then you will need the corresponding socket.

Copper wire

The diameter of the wire should be about 2 mm, the length is about 3.1 cm. I got such a segment from the cable left after the electrical work, removing the insulation from it. Some sources suggest using 4 mm wire. I did not try it myself, so I can not advise.

Construction

Cut a straight piece about 3.1 cm long from the copper wire and solder it to the center pin of the N-socket, keeping the wire as straight as possible. Watch carefully so that the central contact with the side contact is not accidentally closed. The waveguide, or it is a piece of wire, after fixing it on the inner surface of the can, should be 3.07 = ~ 3.1 cm above this surface. You will get the exact length by fixing the nest to the bank and measuring it. The more accurate the dimensions, the better the result and the stronger the signal.

Enter your data and calculate

Can diameter (cm)
Antenna Operating Frequency (MHZ)




Cut-off frequency mhz
Wavelength in a can, Lg (cm) cm
The distance from the waveguide to the bottom (1/4 of the wavelength in the bank) cm
Optimal can length (3/4 wavelength in can) cm
Как построить баночную антенну на 2,4 GHz

Now calculate from the diameter of your can a suitable distance from the waveguide (piece of wire) to the bottom of the can. For this distance is well suited? wavelength of the conductor (guide wavelength). This distance means the distance from the inner wall of the can, and not from the place where the can wall ends. It is also necessary to drill a hole precisely, since how the waves will interfere and, accordingly, how the signal amplifies or weakens, depends on the correctness of the distance. The more accurate the dimensions, the better the result and the stronger the signal. Waves are reflected from the inner walls of the can and therefore, when searching for the right place, it should be taken into account that the bottom of the can is higher than the end of the wall. Then drill a hole in the right place to properly secure the socket. If necessary, drill holes for fastening screws. If you don’t have a drill, you can use a nail and a file. Now it remains to fasten the N-socket with the wire segment soldered to it on the can wall. It does not hurt to peel off the paint at the attachment point, which will improve the contact of the socket with the can. The antenna is ready, you can connect the cable and start testing.

Direction

The signal strength depends largely on the direction, so that the antenna must be directed fairly accurately. For example, I direct it so that I first set it in a horizontal direction, and then carefully move it in a vertical direction. Need to send almost the same as the barrel of a gun, i.e. straight towards the goal. But sometimes it also happens that communication is best when the direction of the antenna does not exactly coincide with the direction to the aiming point. You just have to try.

Cap

Yeah ... to protect against radiation from inanimate and living nature, you need to close the open end of the antenna with something. For example, a suitable plastic cap that allows microwaves to pass through. Whether the lid fits or not can be checked in the microwave, as it operates at similar frequencies. Put the tested lid in the microwave oven with a glass of water (because an empty or almost empty oven cannot be turned on), turn on for 1-2 minutes, until the water boils. And if you find that the cover is heated with water, this material is not suitable for closing the antenna hole, since he does not pass 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 tin cans do not resist rusting for a long time. So if the connection starts to deteriorate and the direction (aiming) of the antenna, etc. no longer helps, it is worth going to the store for a new can.

It also attenuates each connection or each meter of cable connecting the antenna and network card. My approximately 10 meter cable attenuates the signal by at least a couple of decibels. So, the less stuff there is, the better.

Those. specifications

Used Buffalo AirStation WLI-PCM-L11G card, at a frequency of 2425 MHz. Access point is located on the mast , at a distance of approximately 1-1.5 km. The best stable signal I received, directing exactly my bank, was this:

  • Link Quality: 13/92 (link quality)
  • Signal level: -85 dBm (signal level)
  • Noise level: -98 dBm (noise level)

For comparison, the previous "antenna", which was a sticking out piece of wire, behind which was a piece of tin, showed such maximum results:

  • Link Quality: 6/92 (link quality)
  • Signal level: -91 dBm (signal level)
  • Noise level: -98 dBm (noise level)

Signal gain of 3 db means almost twice the signal improvement, in my case it is a fourfold difference. Link Quality at about 6-9 allows the data to move at a speed of ~ 150-250 kb / s, so at 13 it would be a pretty good speed.

By the address http://www.turnpoint.net/wireless/has.htm You will find homemade antennas that show better results, but have been tested at a shorter distance and a bit better visibility.

Cost of

My antenna cost me about 45 CZK, since I already had a piece of wire and a bank. On the search banks and the construction of the antenna was spent about 2 hours. It did not take into account the time spent on the manufacture of fasteners for banks. The cost of the same commercial antenna would probably be four-digit.

A photo

Side view

Fixed antenna 1

Fixed antenna 2

Fixed antenna 3

Bank inside

Bank outside

Photo of the first antenna or what happens when you thoughtlessly cut the top edge of the can :)

The bank with the best signal (canned pineapples d = 9.9 cm. L = 11.5 cm) - but with a wavy bottom and walls and shorter than ideally - didn’t work because it had a hole in the samples in several places.

The mast is at a distance of 1-1.5 km.

Additional Information

(c) Asko Tamm 2002