Biquadratic antenna proposed by K.P. Kharchenko (1961) to catch meter television channels. Of course, the size was large: the wavelength did not differ in small size. When you need an antenna for a modem, assembled from improvised means with your own hands, you can often fit the design in a round box from under the laser discs, the reflector in this case is easy to install. Enough for one disc, the main thing is to look at the light so that it is not transparent (a metal layer is required to construct the reflector). This means: the coverage is suitable, perfectly reflects the waves of digital communications. We are talking about antennas for the modem - it implies two standards WiFi, 3G. The first mastered the frequency of household appliances, interferes with microwaves, the second is the brainchild of cellular communications. The wavelengths are, of course, similar.
Digital modems
The word modem is a derivative of the other two:
- Modulator.
- Demodulator.
Passing information packets, you have to code. Practitioners quickly discovered: if you radiate a person’s speech on the air, the broadcast will fade out at a distance of 25 meters. Low frequency radio waves are not viable. The situation is better with wires. It is well known: analog telephony was able to transmit speech for kilometers, using the help of amplifiers, the frames can be moved apart. However, in this case, the conditions are alien to ideal. Why absurdity occurs. Each medium (air, iron water) is endowed with a capacity characteristic, and the magnitude of the losses depends on the frequency. The atmosphere revealed communication windows (transmitting electromagnetic radiation) used by satellite broadcasting. The WiFi range (2.4 GHz) does not apply, on the contrary, the radiation is absorbed by water vapor.
Thinking in this way, the engineers gave birth to the idea: information can be transmitted by encoding with a useful signal the parameter of the carrier wave entering the transparency window. On the receiving side, the information needs to be decoded. This is what modems do. Light, electromagnetic waves are transmitted in lines, encoded with useful information. Antennas are busy converting electrical vibrations into an ether wave that travels in space. This step eliminates the need to install a communication line, wire. The ether will serve as a transmission of information. You have to pay for amenities, in our case the range is very limited, in addition, 99% of the energy is wasted if you do not use a pair of directional antennas aimed at each other. Broadcast WiFi, 3G network inevitably leads to losses. However, the convenience of mobile communications pays for energy.
In what cases will the external antenna for the modem help:
- We see the reception on the balcony, inside the apartment there is silence. The window sill is caught, inside the room - a round zero. The situation is the scourge of wireless networks for one simple reason: transmitter power is limited by law. Electromagnetic waves are harmful to health, despite the desire of officials to profit, sometimes they have to give in to the elementary requirements of doctors. Not sick, others - developing laws governing the use of hazardous drugs.
- It broadcasts several towers - residents are faced with this situation: a modem flavored with a smart driver stubbornly imposes a connection on a point transmitting worse. In the best case, it is possible to transfer manually, even at times it bothers. A directional antenna will help, which we aim in the right direction.
- In the penumbra zone, the reception of WiFi, 3G signals is uncertain, determined by the vagaries of the weather. A directional antenna, aimed in the direction of broadcasting, helps.
There are other cases. Wherever you want to improve the quality of reception, you need a homemade antenna for the modem. True, one device was invented that allows to increase the signal level. We mean a reflector. Customers saw a 3G amplifier in the store, representing a cylindrical surface: a modem flash drive was installed along the axis. Rays gathered in the center, improving reception. The device is passive, at a price exceeding a modem with a package for six months of the Internet. Not surprising is the question of the townsfolk the size of a mountain, how can an antenna for a modem be made with its own hands.
Modem Antenna Designs
Let's start the Kharchenko biquad antenna, suitable for all digital communication ranges. The instance that catches WiFi fits in a box of laser discs, convenient in terms of weather protection. Would recommend using online calculators, conducting calculations. Since it is difficult to find, they took the trouble to calculate the parameters for some cases, then readers will generalize to any frequency, because the relationships will become obvious. WiFi frequencies:
- Frequency 2.6 GHz, wavelength 115.3 mm. The side of the square will be a quarter of the wavelength: 28.82. To get the total length of the eight, we multiply one side by 8, we get 230.6 mm. We take the stock, it turns out 235 mm. The distance to the reflector will be 0.15 - 0.2 wavelengths. We take something average - 0.175. It turns out 20.2 mm.
In fact, the 2.45 GHz wave is often used. We will carry out the calculation.
- Frequency 2.45 GHz, the wavelength is calculated by dividing the speed of light by a number. Approximately the speed of light of a vacuum is 3 x 10 8 m / s, the exact value is 299792458. We calculate the wavelength ... it turns out 122.36 mm. Next, we carry out the calculation in the beaten way. We get the side of the square, dividing the wavelength by 4 - 30.6 mm. The length of the wire is calculated by multiplying by 8, it turns out 245 mm, take a margin of 250. The distance to the reflector will be 112.36 x 0.175 \u003d 21.413 mm.
It is difficult to bend the wire at a right angle. We recommend using a vise, a pair of pliers, a hammer when manufacturing an antenna for a modem. Along with the ruler and corner, of course. Many people have the question of how thick the wire itself should be. Let's try to answer! Reducing the frequency of the diameter increases, at 2600 MHz the parameter is 2.75 mm; mastering 1300, therefore, should take 5.5 mm. Here are a few values:
- 900 MHz - 8 mm;
- 800 MHz - 9 mm;
- 1800 MHz - 4 mm;
- 1900 MHz - 3.8 mm.
Similarly, we get the result for any frequency. It is clear that violation of the thickness, removal from the calculated values \u200b\u200bwill not lead to fatal consequences, but you should not get too carried away. In order not to say later that the VashTehnik website contains incorrect values \u200b\u200b... According to our information, the GSM 1800 standard is often used in the territory of the Russian Federation, let's see what Harchenko biquad antenna should be at the operating frequency (3G modem).
The frequency is 1800 MHz, we find the wavelength: 299792458/1800000000 \u003d 166.6 mm. We find the side of the square by dividing by 4, it turns out 41.6 mm. The total length of the wire will be 333.1 mm. With a margin of 335 mm comes out. The distance to the reflector is 166.6 x 0.175 \u003d 29.15 mm. The thickness of the wire is indicated above. Design for health.
Other wavelengths will be time to consider, the calculation procedure is obvious. Here are a couple of comments on the design of a homemade antenna for the modem. If there is one biquadrat (and we will meet more), it resembles an eight - no more. There is no intersection at the center point. It’s just that the wire draws together without touching, then runs back to the sides. It reminds, indeed, the figure eight laid to one side (WiFi polarization is vertical). For another polarization - horizontal - we place the figure eight vertically.
The wire for the antenna is better to take insulated. The cable core of the desired thickness is suitable. Optionally, the material must be copper, just the Olympic metal is not subject to electrochemical corrosion (it is always an acceptor). Protect the building in any case. As mentioned above, WiFi models are placed in a box of laser discs, which we seal for fidelity.
Eight stands on isolated racks that can be placed anywhere, however, it is easier to use two supports in the area of \u200b\u200bconvergence (in the middle). One edge is connected to the shields of the cable and antenna, the second serves to remove the signal. Both terminals are close to each other, almost in contact, there is no electrical contact at the intersection.
The signal gain will increase if two biquadrats are used. The central part is performed in this way, then the eights intersect (!) Crosswise, but at the point of contact two wires are reliably insulated from each other. The beam pattern narrows, increasing gain. Good techniques for catching a tower that can be seen on the horizon. It will be possible to direct the modem antenna accurately - the reception will certainly improve.
Connecting the device is a standard 50-ohm cable. Ideally, it’s good to measure the SWR, then bring it to a value less than 2. The antenna device for the modem may be different, a recent review of the design reminiscent of that used by cell phones. Emitting areas connected by matching lines.
Concluding the review, we emphasize: cellular standards, WiFi remind each other. In both cases, the polarization is vertical. Made for reliable reception at any point. When the wave propagates around the planet, the configuration is preserved. The vertical polarization is perpendicular to the soil. When talking on the walkie-talkie, try to keep the antenna like that.
Practice! It is known for certain - dumb individuals tend to perform the simplest procedures incorrectly. Acting for show, keep the walkie-talkie horizontally, turning in an inconceivable way. Stick to proven solutions. Sometimes it’s easier to take a couple of steps. A beam rarely changes polarization, otherwise the broadcasting industry would have long taken into account the nuance (auto radios, for example).
Today, many citizens use wireless Internet, but at the same time seek to increase the speed of its work. After all, excellent access is guaranteed when the modem is close to the base station of the mobile operator. In this regard, those who work on the Internet far from the station are content with a low speed. Is there a technical way to help solve this problem? The best option is a 4G antenna with your own hands.
What is the Kharchenko antenna and how does it work
The so-called Harchenko antenna, which is designed for a 3G modem, is a makeshift model. There is nothing particularly complicated about her device. The zigzag design was proposed by the scientist K. Kharchenko back in the 1960s. Today, it is quite popular among hams, not only because of its simple device, but also its excellent repeatability, as well as broadband. The latter advantage relates particularly well to the helical construction.
By their own device models can vary quite a lot. Based on the size of the plate, the frequency of the structure varies significantly. At the same time, it should be borne in mind that home-made antennas can include objects made of plastic and metal.
The antenna for the modem can be of different types. The simplest is omnidirectional. It can receive and transmit a signal in all directions equally intensively. In particular, this may be a simple quarter-wave vibrator. In simpler terms, this is a piece of wire that has a quarter wavelength of the signal that is being received.
A sector antenna may limit radiation in a particular sector. In particular, if you set an iron sheet behind an omnidirectional device, you get a sector design. Its sector will be 180 degrees. A similar iron sheet is called a screen.
The most effective is directional design. Thanks to the right choice of screen curvature, you can make a narrow beam that will emit a radio wave.
The main antenna nodes are:
- the vibrator to which induction, the induction of a wave of electromagnetic waves, which are sent by the transmitter of the cellular operator;
- a cable together with a matching unit transmitting the induced signal directly from the vibrator;
- signal transmission unit from the cable directly to the modem input;
- a reflector that eliminates interference as well as reflected signals to increase the receiving power.
Do-it-yourself Antenna Kharchenko is an excellent device for anyone who wants to have high-quality communication without having to spend large sums of money. It is very simple to make it even for an ordinary person who does not have the appropriate professional skills. The result is really excellent. Such a design will last for a long time.
Making an external antenna
As a rule, an external antenna for a 4g modem is endowed with two square components. The performed calculation of the Kharchenko antenna at a frequency of 2100 MHz shows that the dimensions of the sides of the component should be 53 millimeters each.
However, to reduce the internal resistance of the antenna, craftsmen advise not to make square components, but diamond-shaped ones, in which the angle is 120 degrees.
Detailed instructions are given in this video:
How to amplify a 4G signal?
In order to increase the effective use of the antenna for the USB modem, it is equipped with a reflector - a steel plate. It can be made of foil textolite. The distance between the antenna and the reflector should be 36 millimeters. In order to create a distance between the antenna and the reflector, you can use some kind of cap or box.
Today, there are many different ways to connect to the Internet. At the same time, it cannot be said that they are all equally effective and built on a single principle. In particular, if we talk about operators working with mobile devices, they offer a good Internet connection in those areas that are located in the radius of signal transmission from the towers. It is clear that the farther the signal, the more there will be interference and discontinuities. Of course, the largest mobile operators are trying to create the maximum coverage of the territories of the countries where they work, but this is not always enough.
A 3G antenna helps to strengthen such operator gsm signals. This is a fairly lightweight and simple device that does not require much hassle in setting up and installing. However, if you purchased a 3G antenna, then it is best to entrust the installation of its connection to professionals. In turn, for those who are very knowledgeable in technology, there are a fairly large number of instructions on how to create a 3G antenna with your own hands.
Where is the 3G antenna mounted
A fairly lightweight and easy-to-use 3G antenna can catch the GSM signal of the operator, both indoors and out. In addition to such a device, there is usually a metal multifunctional, durable bracket and a ten-meter cable. With their help, the antenna can be attached either to a high mast or to a wall. In extreme cases, the 3G antenna can be located near the window or directly on the windowsill. Such a device is easy to transport and when reconfigured, it quickly connects to the network. According to the degree of amplification of the antenna signal can be divided into:
- weak
- medium;
- strong.
So, one of the most effective 3G GSM antennas is considered to be the UMTS HSDPA 21 dB 1900-2100 MHz model, which is able to open Internet access even in those areas where the signal is almost imperceptible. This device works with such mobile operators as Kyivstar, Life, MTS, Trimob, Ukrtelecom and Utel. To achieve an absolute result, it is best to use a tandem such as an antenna, a UMTS- or HSDPA-type SIM card and a 3G modem.
The main specificity of antennas with a powerful signal amplifier is the need to fine tune them towards the main station of the mobile operator.
3G GSM antennas, which do not have a very good amplifying effect, are considered the cheapest. They have almost all the characteristics that their more expensive brothers, but are suitable for cases in which the signal source is located in close proximity.
The middle segment of 3G antennas, in principle, is able to provide Internet transfer from a GSM operator to a computer, even if the degree of coverage does not apply to green areas. It should be remembered that in this case the quality will not be too high and the signal may be interrupted.
Do not think that the ideal and only true option for the acquisition is a 3G antenna with a powerful signal amplifier. It is certainly universal, but due to the highest cost it is not always appropriate. If you do not need to significantly strengthen the existing GSM-connection, then a cheaper option is also suitable.
How to create a do-it-yourself 3G GSM antenna
Despite the fact that 3G GSM antennas are relatively inexpensive and are sold in almost any mobile phone store, however, if you can’t afford this thing at all, you can do it yourself.
Step 1. First things first, it is advisable to find and download a special program on the Internet that allows you to calculate the quadratic antenna with a few keystrokes. Further, to create the design itself, it is desirable to prepare the following materials:
- RG6U wire and connector for it;
- copper wire, 1-4 mm in diameter;
- a small plastic cover (a cap on deodorant and shaving foam is suitable);
- a small sheet of plywood 120x134 mm;
- foil;
- soldering iron;
- solder;
- rosin.
Step 2. After the tools are prepared, we take the wire and fold it in such a way that we get two interconnected squares (butterfly). Each side of both squares should be equal to 53 millimeters. 
Step 3. The ends of the wire should coincide in the middle of the connection of the squares and they must be soldered to one end of the antenna wire, apply solder to the opposite corner of the wire and strip it all with the connector. The central core of such a wire must be arranged so that it protrudes from the connector by about 1 cm. 
Step 4. Then it is advisable to solder the wire braid using the same rosin. If this does not work out, then it is easier to solder the core of the wire to the side of the connector body.
Step 5. After that, foil is used. It is necessary to wrap plywood and punch in the middle a small hole for the wire. Thus, we get a reflector for the antenna. At this stage, it should be borne in mind that the frame should be located 35 mm above the reflector. A pre-prepared plastic lid is able to provide this. 
Step 6. It should cut several grooves of 1 cm. After this, we position the antenna at the desired level, about 4.5 cm. Finally, we fix the reflector and that's it, our homemade 3G GSM antenna is ready.
Checking Antenna Operation
At the next stage, you need to check how our 3G GSM antenna will interact with the modem. If the modem does not have a connector to connect it to, you can use the antenna-to-antenna method.
Thus, our home-made device will capture a signal from another design, which will assume the function of a repeater. To carry out such work, you need to protect the core by about 10-15 centimeters from the other end of the wire, which comes from our 3G GSM antenna. But to ensure the most powerful signal, it is necessary to attach a foil strip of 7-9 centimeters in type of circular polarization to the edge of the wire braid.
High-speed Internet is becoming more accessible, and perhaps, after just a few years, a resident of even a remote area can manage it. But now those who live outside the city, or even just in small towns, have to be content with alternative options, one of which is the use of a 3g modem. As a rule, he catches the network quite well, being not far from the transmitting base station, but as you move away from it, the signal level will decrease. The antenna for a 3g modem made from handy materials can help to amplify the signal.
The fact is that even if there is a desire to buy a factory version, it is not always possible to do this, and not every modem has additional inputs for connecting an external antenna. Of course, you can do soldering wires directly to the board, but if we are already engaged in such interference in its device, then it’s worth a try. There are several basic options for such antennas, and methods for their implementation.
Types of DIY antennas for 3G modem
Antennas can be divided into omnidirectional and directional, that is, "looking" in a specific direction. The latter, of course, require knowledge of at least the side from which the stronger signal is coming from, but this is also solved by the usual test by gradually scrolling it around its axis.
Among the most famous industrial models, which are much less commonly used in self-assembly, is the 3g panel antenna. It is a little more difficult to assemble it with your own hands than other options, but due to the design features, in some cases, the factory version was still preferable.
The antenna of the yagi is time-consuming, but with the correct assembly it can significantly increase the signal level. Not recommended for users who are not very confident in the hands of tools.
The Kharchenko antenna is a lighter version than the above, and requires less material. A plus is also the size, which can be several times smaller than that of the yagi antenna.
The last method of manufacture, you can call the elementary use for this purpose of ordinary cans of coffee, or other drinks. In a previous article, a similar device was mentioned.
DIY yagi 3g antenna
Of the materials for manufacturing the antenna, you will need: a metal rod with a diameter of 18 mm, electrodes with a diameter of 4 mm, a plastic clothes hanger (79 mm) and a T-shaped PVC pipe connector as a holder for the future vibrator, self-tapping screws.
The vibrator is made by cutting off the top of the plastic coat hanger as shown. Then it is inserted into the holder, which will subsequently be screwed onto the bar using self-tapping screws.
We mark on the rod places for electrodes, which as a whole make up the reflector. Its length will be 81 mm, the distance from the beginning of the bar: 30 mm. We drill holes for the electrodes, which will then be tacked into them by welding, so that the design shown in the figure is obtained. This whole system of teeth is a do-it-yourself 3g yag antenna reflector.
The last item we make the antenna loop for the vibrator. In principle, it can be done separately, and installed at the beginning of the process - to whom it is more convenient. In any case, it is created from an ordinary wire, and does not look like something particularly complicated. It connects a vibrator and the last of the reflector electrodes.
The finished one is then attached as high as possible above the ground, or a pin-base can be attached to it, similar to those used on simple television antennas. Here you can not think about the diameter of the material and the like - the most important will be its composition. It is impossible that it could cause interference with signal reception for a 3g modem.
Antenna Kharchenko for a 3g do-it-yourself modem
Harchenko’s antenna is also called the “eight” and there are no difficulties in its manufacture. The basis of the design, which attracts attention, is a curved wire, beyond which the antenna is called the “eight”. An ordinary 4 mm wire is bent as shown in the figure, and its ends are soldered together. We observe the angle between the walls of the antenna, which is 120 degrees. The length of the side wall is 53 mm, and the distance between the points at which the two squares of the antenna are connected should be 5 millimeters. In no case do we bring it to a smaller size, or even less to zero.
We look for, or make independently, a 2 mm thick aluminum plate. The length of each side is 140 mm. In the center, you need to drill a hole for the coaxial cable, which will go from the wire element of the antenna to the modem. We attach the wire itself parallel to the plane of the plate at a distance of 36 millimeters. For fastening, holders are used made of materials that do not conduct electricity, for example, plastic racks.
We pass the cable through the hole in the plate, and connect the cores to each of the two points of the "eight" at the junction of the "squares" - to the very points between which we previously left a distance of 5 mm. It remains only to connect the opposite part of the cable to the modem.
It remains to "dress" the modem with copper foil, which is sold in the radio store. We cut out a piece, 45 mm long, and of suitable width in order to wrap the modem several times around it, and solder it so that it does not split. A wire will be connected to this base. Now, from the same foil, a braid for a modem with sides of 27 and 76 mm. It is important that subsequently she herself does not touch to the central core connected to the foil on the modem. We do, as in the figure below, and achieve the appearance of a stable signal.
Antenna for 3g from a can
The simplest, probably, version of the directional 3g antenna with your own hands is a design made of a simple can. In previous articles, I talked about how to make an amplifier for wi-fi in a similar way - there is about the same design, but only it works already for reception, and not for transmission.
A hole is made in the metal can into which the modem itself is inserted, or, if it has the corresponding antenna jack, the end of the television cable connected to it. The length of the protruding part inside the can is about 36 mm with a can diameter of 100 mm. In this case, the hole should be located in the last third of the can, at a distance of 65 mm (for our case).
With the resulting antenna, it remains to walk around the room to catch the signal direction, and, if possible, hang it higher, for a more stable connection. In cases where the signal is completely absent, a can antenna is unlikely to help, but to amplify an existing one, it is.
Many of us have been using devices such as modems from mobile operators for a long time and enjoy access to the World Wide Web. But unfortunately, unlike broadband wired Internet, such devices have several significant drawbacks. The main one is the features of the propagation of the radio signal in the surrounding space. Radio waves in the 3G, 4G and LTE bands have a bad property of reflecting from obstacles, scattering and attenuating, respectively, the speed and quality of the Internet connection is deteriorating. What can be done in this situation?
The easiest and cheapest way to amplify the signal coming from the provider's base station to your modem is a do-it-yourself antenna made from improvised means. Let us together consider the simplest and most popular options for the manufacture of structures that enhance the radio signal received by the modem from the BS.
Wire antenna
The simplest version of a homemade antenna is the use of a piece of copper wire of a small cross section, which must be wound in several turns around the top of the modem. The remaining end of the wire with a length of 20-30 centimeters is bent vertically. This primitive method under certain conditions can significantly enhance the stability of the received radio signal. 
Can
Probably, in any house you can, if desired, find an empty used tin can from soft drinks or coffee. This simple item can become the basis of another homemade antenna. We remove the container lid, make a hole in the side wall, insert the modem there up to half of the case, and use a USB extension cable to connect to a computer or laptop. Then it remains to find the best arrangement of the structure in space. The amplification effect in this case can be very good. 
Colander 4G
Most people have the usual aluminum colander. And this item of utensils can be used to create another simple antenna for the modem. It is only necessary to fix the “whistle” in the bowl of dishes, for example, using adhesive tape. As they say, all ingenious is simple. 
Frame zigzag antenna of the famous Soviet radio amateur Kharchenko. To make such an amplifier, you need a copper wire with a cross section of 2.5 mm. We bend it in the form of two aligned squares, at the connection point we place a modem connected via a USB cable to the computer. From the back of the antenna we attach a thin sheet of metal as a reflector. You can make such a device quite quickly, and the gain under certain conditions can be very pleasing. 
Converted Satellite Dish
Many of us use satellite TV. And if you have an old satellite dish at your disposal, then it can be altered into an antenna for a 4G modem. It is very easy to do. We remove the converter from the rod and mount the modem in its place. We direct the design towards the provider’s base station, slowly rotate it until the best result is achieved. 
So, we examined several options for making the antenna for a 4G modem with our own hands from available tools. You can try to make any of the proposed models yourself and significantly enhance the signal received from the provider's base station. Good luck
