How does a short car antenna work. Car body as an antenna

06.06.2016

Trips without a tape recorder in the car turn into a real boredom. It is much more interesting to set up your favorite radio station and plunge into the world of listening to your favorite music. And indeed, it is more comfortable to move even on a boring country road. But one of the main problems for motorists is the choice of antenna. Many car enthusiasts often do not know which characteristics are the most important, as well as what to pay attention to when choosing. Let's consider these questions in more detail.

Purpose and characteristics

The task of the antenna is to convert electromagnetic waves from various sources into a special signal in the form of an electric current. The reverse process is also possible, when the electrical signal is converted into EM waves. This option indicates that the same antenna can perform several functions - to pick up the signal and transmit it. If the antenna itself is not capable of catching a signal, then no amplifier is able to help it.

The first thing to pay attention to is the size of the antenna. It is known from the course of physics that EMs have two main characteristics - the length and the polarization vector (the parameters refer to the magnetic and electrical components). In the case when it comes to the electrical part, the waves are divided into two types - horizontal and vertical. Radio stations operating today work on the principle of vertical polarization. In turn, stations that broadcast television, on the contrary, operate on the principle of horizontal polarization. When choosing an antenna, it is worth considering its parameters, which must be commensurate with the long wave. As for the polarization of the waves, not only the size is important here, but also the correct choice of the position of the product.

The dependence of the size of the antenna and the length of the received (sent) waves is a whole science. If we explain this point in simple terms, then the requirement is due to the need to enter into resonance with EM oscillations. Only in this case, the antenna will work with maximum efficiency, and convert the EM wave into a voltage of the required magnitude. Subsequently, the electric current can be amplified and converted in the radio (receiver).

The concept of tuning is important for the antenna, because in this case the latter will be able to selectively receive certain signals. On the other hand, the final selection process lies with the receiver. If you believe the technical justifications and the experiments carried out, then the antennas that have the usual form of a pin show the greatest efficiency. In this case, the length of the device should be equal to a quarter of the wavelength of the middle part of the range.

• 1. Outdoor antennas.In this case, the signal that is received by the antenna is sent to the receiving device without loss of quality. But to achieve such results, the antenna must be coordinated with the feeder (cable), and the connecting cable with the radio. These conditions are easy to meet if the antenna has ¼ length, the cable resistance is 75 ohms (for a television cable), and the receiver input is correctly calculated and correctly executed.

The quality of the distribution of waves in the air is closely related to the wavelength. So medium and long waves go around the surface, that is, they are distributed globally. As for short waves, here propagation occurs due to multiple reflections. There are also ultrashort waves, which are the weakest and work only within the line of sight. Moreover, each of the wave types has its own purpose.

For example, long and medium waves in car antennas are only needed to receive a radio signal. Here, there is no need to manufacture any special antennas, because such signals have sufficient power. If the antenna caught the signal, then it will be of high quality (the principle of such reception is often called “on a nail”).

The principle is similar when operating in the short wave range. The only difference is that communication is already available here. In addition to the amateur communication option, a “piece” is also allocated on HF for vehicle owners. The operating frequencies here are 26.97-27.85 MHz. Such ranges are called CB (CB).

Most modern antennas are tuned to receive ultrashort waves. In this case, the reception range is limited to frequencies of 66-108 MHz. Here it is worth highlighting two categories of frequencies - "Soviet", which was adopted back in the USSR (66-74 MHz) and "foreign", operating in the range of 88-108 MHz (FM waves). The name FM stands for "frequency modulation" or frequency modulation. It turns out that when designating the type of antenna, we are guided by the wavelength, and abroad - by the type of its transmission. At the same time, the subtleties of the work remain unchanged.

• 2. Internal antennas.If the antenna is internal, then it can be of two types - removable and stationary. In the latter case, the product is glued into the glass. The main convenience of internal devices is reliability. They are difficult to break or steal. Another thing is that the signal quality of such products leaves much to be desired. The problem is that the "antennae" of the antenna are horizontal, despite the fact that the signal coming to the antenna has a vertical direction. In addition, in the city, the signal changes regularly, which complicates the "life" for the antenna. But it is worth leaving the city to face a number of problems.

To promote and popularize the product, manufacturers supply antennas with special amplifiers that improve signal quality. On the other hand, if the antenna is not able to receive the signal, then the amplifier will be useless. Antenna amplifiers are good when there is a long wire between the antenna and the receiver (often it is this that causes signal degradation).

It is believed that if the wire length is up to 5 meters, then when driving outside the city (when there is no normal signal), the amplifier is ineffective. All he can do is amplify the noise, and within the city - add interference. This is why many antenna designers put in dedicated city-highway switches. In fact, the principle of operation of such a system is simple - when switching to the "city", the amplifier turns off.

Practice shows that the best amplifier is a high-quality antenna, and the best choice of antennas is the installation of an outdoor product (taking into account polarization and wavelength). If we consider the FM range, then the highest sound quality can be achieved from a pin having a length of 75 centimeters.

The main disadvantage of outdoor antennas is that they are easy to break. That is why, when choosing such a product, you should focus on the height of the garage and the design features of your car. It is also worth considering in advance the subtleties of the cable to the receiving device, the place for installation and other points. The best cable option is the use of a shielded and solid product, in which there are no solderings or joints at the entire distance, from the receiving device to the antenna itself.

• 3. Anti-static antennas.Separately, it is worth highlighting another type of device - "miraculous" antennas, which, according to manufacturers, are able to remove static electricity from the car body. A similar innovation in the automotive industry was spied on in the aviation industry. So, on airplanes there are special “brushes” on the edges of the wings, the task of which is to eliminate static charge. Here the principle is the same. But this does not work in cars, because in order to eliminate the appearance of a static charge, the car must move at the speed of the aircraft. In addition, anti-static antennas are fixed with double tape, which, together with the paintwork, makes the process of removing static impossible.

Antenna parameters

• wave resistance.Standard antennas that operate in the CB band have a wave impedance of 50 ohms. In some cases, they are connected to the receiver via a coaxial cable that has a resistance of 50 ohms (usually PL-259). The personal wave connection of most antennas has a volume equal to 50 ohms. That is why a matching device is switched on between the feeder and the antenna. The main difficulty is that it is impossible to measure the wave resistance using a special device.

• Number of channels or bandwidth.This parameter characterizes the frequency range in which the antenna is able to operate without tuning. The difficulty is that the SWR parameter at the bandwidth limit is often not specified in the parameters, so it is not possible to compare the bandwidths of different antenna models. But there is a way out. Due to the fact that the grid spacing between the channels is 10 kg, it is possible to determine the bandwidth of the antenna by the number of channels. The formula looks like this: Bandwidth (kHz) = Number of channels * 10 kHz.

• Gain.This indicator shows how many times the signal at the antenna output changes in comparison with the same indicator of the reference device. During the measurement, the signal from one radio station is taken into account. Antenna gain measurement is given in relative units. The problem is that manufacturers do not always prescribe this parameter on their devices. Experts recommend that when buying an antenna, focus on the gain, but do this with great care. And here it is worth considering the size of the antenna. So long products are characterized by great reinforcement. Specialized antennas with an extension coil provide more gain than antennas of the same size.

• Conducted power.By this parameter, one can judge the maximum power that a transmitter can have if this antenna is used. If the maximum power rating is exceeded, breakdown or thermal breakdown may occur. For industrial-type antennas, a power limit of 10 watts is permissible.

• Wind resistance.This criterion is important, although many motorists ignore it when choosing an antenna. According to the wind resistance index, one can judge at what wind speed the antenna can be destroyed. It is especially important to pay attention to this indicator in regions where hurricane winds occur. In addition, antennas that are mounted on a magnetic base are subject to wind.

The first radio receiver for a car appeared in 1930, and to this day the radio in the car remains relevant. The small size of the car does not allow the installation of large antennas, so motorists widely use active antennas. Read about these devices, their purpose and types in the article.

Purpose of the active antenna

For any radio to work, an antenna is needed - a device that receives electromagnetic waves and converts their energy into an electrical signal. Further, this signal can be subjected to amplification and conversion, which is what the radio receiver does. Confident reception is possible only if the antenna is tuned to a certain frequency or frequency range - this setting is carried out by selecting the length of the antenna. In the simplest case, the antenna can be a half-wave or quarter-wave stick. For example, for the FM broadcast band, the wavelength is approximately 3 meters, respectively, the length of the antenna should be from 0.75 to 1.5 meters.

It would seem that 75 cm is not much, but even for a car this is a significant value, it is difficult to place an antenna on a car of such a length, and it can even spoil the appearance of the car. Therefore, antennas shorter in length are more often used, but they are less sensitive, they convert the energy of an electromagnetic wave worse and supply a lower voltage to the input of the radio receiver. That is, a short antenna worsens the reception and playback quality of a radio program, or even makes it impossible to receive some radio stations (especially remote ones).

This circumstance led to the need for short, but sufficiently effective antennas that would ensure successful radio reception in a car. To solve this problem, active antennas were created - short antennas with high sensitivity.

An active antenna is an electronic device that combines a conventional antenna (whip or dipole) and an RF amplifier. Such an antenna can receive a weak signal and provide the same radio performance as a conventional extended length antenna. Also, active antennas can perform some other functions, which are described below. But first of all, you should look at what types of active antennas exist today.

Types of active antennas

On the market, you can find antennas that differ in design, installation location, type of installation and functionality.

By design, antennas are divided into two main types:

• Whip - a metal pin of one length or another is used as an antenna. In modern antennas, the pin has a plastic protective sheath. Typically, external antennas are made of this type;
• Dipole - reception is carried out on a symmetrical dipole, spaced pins of the same length. The scheme is typical for interior antennas.

According to the place of installation of the antenna, there are:

• External - mounted on the roof, in the front or rear fender, etc.;
• Intra-salon - mounted inside the cabin, on the windshield or rear window.

Both types of antennas have their advantages and disadvantages associated with the presence of a metal body. As you know, the metal does not transmit radio waves, so the body of the car serves as a screen, inside the cabin the electromagnetic field strength is several times lower than outside. Therefore, interior antennas are mounted on the windshield. However, the bodywork serves as an additional protection against interference (especially coming from cars located in adjacent flows and behind), while the external antenna receives all interference.

By type of antenna mounting are:

• Intrasalon - on double-sided tape;
• Mortise antennas are external antennas rigidly mounted in the body or in a special container (retractable antennas);
• On a magnetic base - usually external antennas for quick installation on the roof.

The main function of an active antenna is signal amplification, however, modern antennas may have various additional functions:

• Switching between ranges;
• Sensitivity change - "City" mode with less sensitivity and "Route" mode with increased sensitivity;
• Interference protection.

Also, active antennas can be divided into several groups according to their purpose and operating ranges:

• Antennas for any one or two bands - usually FM or AM / FM;
• TV antennas;
• Universal antennas - for all bands from AM to TV.

All active antennas, regardless of type, have a similar design and a single principle of operation.

The design and principle of operation of active antennas

Structurally, any active antenna consists of five main parts:

• Antenna (pin or dipole);
• Amplifier (in a plastic case);
• Antenna cable (supply cable);
• Wire or separate power supply cable (optional);
• Ground connection wire.

Cabin antennas usually have a dipole design. Dipoles are made in the form of so-called canvases - flexible conductors in a plastic sheath that can be fixed on glass. The canvases come out directly from the case in which the amplifier is located, the whole structure is attached to the windshield using double-sided tape.

The active antenna works quite simply: the signal emitted on the canvases is fed to the amplifier, after which it is fed through the cable to the antenna input of the radio / radio. The amplifier requires power and ground to operate. Power can be supplied with a separate two-wire wire, it can also be done according to the standard scheme - by connecting the ground wire to the body (to any bolt that is located next to the antenna) and the second wire to the "+" battery.

Compact antennas with quick installation (on a magnetic base) usually do not have a separate ground, and are powered from the cigarette lighter. Such antennas are small and easy to install, but they give less gain and are generally worse even compared to in-cabin antennas.

Features of installation and operation of an active antenna

Installation of an external antenna, especially a mortise one, should be entrusted to specialists; an internal antenna can be installed independently. The installation of the antenna in the general case is reduced to the following:

1. Choose the optimal location of the antenna on the windshield or rear window;
2. Glue the antenna body and antenna sheets using the included double-sided tape (the sheets are already covered with adhesive, covered with a protective film);
3. Degrease the glass at the place of gluing the antenna body and cloths;
4. Connect the ground wire to the car body (to any bolt or directly to the area of ​​​​the body cleaned from paint);
5. Connect the lead cable to the antenna input of the radio / TV;
6. Connect the power cable in any convenient place to the “+” power source (the best option is to the radio terminal).

Particular attention should be paid to the installation site of the antenna, here you need to follow a few recommendations:

• Antenna sheets should be located at a distance of at least 5 cm from the edges of the window (this reduces the shielding effect of the car body);
• The ground wire should be as short as possible;
• The power cable must be connected as close as possible to the radio/cassette recorder.

It is necessary to position the canvases parallel to the edge of the window, and two options are possible here:

• Along the upper edge of the window - the canvases are elongated;
• In the corner of the window - the canvases are located at a right (or so - depending on the geometry of the glass) angle.

When connected correctly, after the ignition is turned on, the LED on the antenna housing will light up. An active antenna does not change the operation of the radio and in the simplest case does not require any additional steps. If the antenna has additional functionality, then it may be necessary to switch the "City" / "Route" modes or select ranges - how to do this is usually indicated in the instructions.

An active antenna, when properly installed and used, improves radio reception and makes driving more enjoyable. This is a simple, inexpensive and interesting solution that every car owner can afford.

This development was made for professional needs. Hidden and protected on the car was required. The decision was not given immediately - slot antennas are little known, and they are used very rarely on HF. It took a long time to prove to customers that This can work (which is ridiculous, right after the field strength measurements showed that the antenna radiates normally). It caused children's excitement in many: they covered the car with a net, and poured water over it, and put it in the water on the bottom. Nothing helped, the piece of iron body stubbornly continued to radiate. One of the most repeated things - I know of more than 2000 cases. The magazine article in 1996 was for promotional purposes and much was omitted. But even in this form, it was repeatedly "torn off" on different sites. Below is an extended version of the article, including the very subtleties omitted in the journal.

Car body as an antenna

When using radio transmitters in automobiles, the most difficult task is the implementation of a matched antenna. This article discusses the principle of using a car body as a hidden and coordinated transmitting antenna at frequencies from 20 to 200.

Overview of existing types of car antennas

The minimum dimensions of the effective radiator must be at least l /4. With a decrease in size, its efficiency drops very sharply: in proportion to the square of the shortening. When the antenna is transmitting, its low efficiency irrevocably reduces the radiated power and, accordingly, reduces the radio range. Therefore, despite all the advertising assurances about the effective operation of very small miracle antennas, one must be treated at least ironically.

The simplest car antenna is a rod shortened from the bottom of the coil on the roof. This is a good solution, except in cases where an outdoor antenna is unacceptable (security systems, tracking, covert radio communications). In these cases, it is necessary that the antenna be hidden and inaccessible to external influence (the hijacker will first break the external antenna, and the security device becomes useless).

To solve this problem, as a rule, a short helical antenna is used, located inside the cabin near the glass. It is actually a rolled l / 4 pin, but since it is placed inside a metal body, its effectiveness is greatly reduced due to the shielding effect. In addition, the helical antenna has a very narrow bandwidth, which requires careful tuning of the antenna and makes it impossible to use it over the entire frequency band.

Using the car body as a slot antenna

Our task is as follows: to find a constructive gap in the car with a total length of at least 1.5 ... 3 m (for efficient operation in the 20..30 MHz range) and ensure its excitation. You can find several such places on any car, but it is desirable that the slot configuration be approximately the same for different types of cars so that the antenna itself, its parameters and the cable matching device are unified.

It is also necessary to minimize interference in the car structure when making a slot excitation device, because it is only theoretically good to connect the RF in the center of the slot, but in practice, if you need to peel off the paint and drill, then few will go for it.

In view of the foregoing, a gap was selected between the trunk lid (VA3 2101-2107 and similar) or the back door (VA32108, 2109, AZLK2141 and similar) and the car body. To ensure excitation, it is necessary to insulate the latch of the trunk lock as shown in Figure 1.

At the same time, the input power points of the slot are standard bolts for fastening the trunk lock latch, screwed into the body (body output), and the lock latch isolated with additional gaskets from the fastening bolts, which has mechanical and electrical contact with the trunk lock and with the trunk lid (signal output) .

This design is very similar to the isolation of metal transistors and their bolts from a radiator, and is not difficult for a radio amateur. The specific method of isolation may be different (depending on the design features of the car), the main thing is to ensure that the electrical circuit is broken through the trunk lock, and to provide the ability to connect wires there. One wire should go to the trunk lid, the other to the body shell.

Please note that this is a slot antenna, so the trunk lid should not only not be isolated from the body in its rotary hinges, but, on the contrary, it should have a high-quality electrical contact there. If there is none or there is, but it is bad (old hinges with rust), then it is necessary to lay a flexible bus connecting the trunk lid in hinges to the body (approximately the same flexible jumper made of thick braided shielded wire, which is installed to reduce interference from ignition). Moreover, such jumpers must be installed in two places - one near each loop.

Everything, the mechanical part of the antenna manufacturing is completed. It remains only to connect a coaxial cable to the petals and take measurements. Figures 2 and 3 show the experimental dependences of SWR on frequency for some vehicles.

"Moskvich" AZLK 2142 and "Zhiguli" VAZ 2109 have an almost identical first resonance of about 65 MHz (at this frequency, the size of the car is about half a wave). The third harmonic differs more significantly, since it is strongly influenced by the shape of the car.

For Volvo 249, VAZ 2104, VAZ 2106 and similar cars, the resonances are higher, which indicates that not the entire body is excited, but only the trunk area and the metal adjacent to it. As a result, we have a finished slot antenna with several resonant frequencies, one of which coincides with the operating frequency. It is enough to connect the power cable to the points with the appropriate. But such a coincidence is rare. As a rule, the input impedance of the slot at the operating frequency is complex, which excludes the direct connection of the supply cable.

Since the dimensions of the slot are determined by the design features of the car and we, of course, cannot change them, to ensure the SWR in the cable is close to 1, it is used, which ensures the transformation of the complex impedance of the slot antenna into active, equal to the wave impedance of the cable used. SU is placed directly near the feed points of the slot. That is, the picture is almost the same if they had a dipole of fixed sizes - low SWR at resonant frequencies and complex input impedance at all others. And in the same way, for excitation not at the natural resonant frequency of the antenna, a control system is required at the feed point.

In the range of 20-30 MHz, the slot reactance is inductive, and the active resistance lies within 8...15 Ohm (series equivalent). To match the cable in this range, the control system shown in Figure 4 is used.

Broadband transformer TV1 1:4 (on ferrite, ensuring operation at a given power and frequency) matches the cable resistance of 50 ohms with the active part of the radiation resistance of the antenna, and capacitors C1, C2 provide compensation for the inductive component.

The box with the SU is mounted (on self-tapping screws) directly at the trunk lock. The CS output is connected by a short (no more than 50...80 mm) and thick (wire cross section 1..3 mm 2) twisted pair of insulated wires to the trunk lock petals.

The specified value of C2 refers to the section 25 ... 28 MHz, at lower frequencies, the capacitance C2 must be increased. Exact matching is achieved by a single adjustment - capacitor C2. With a 50 ohm cable at a resonant frequency, SWR is not more than 1.3. Slot Antenna Bandwidth at 27 MHz by SWR Level<2 составляет 500..800 kHz. Это СУ обеспечивает хорошее согласование с большинством типов автомобилей.

Perhaps in the specific case of your car (a different slot configuration, a different frequency) there will be problems with matching. In this case, we can recommend the following method:

1. Connect a half-wave length of cable (electrically half-wave, taking into account) to the slot for the desired frequency. Moreover (important) you do not connect it directly to the petals of the slot, but through that twisted pair (determine its length yourself, based on the design possibilities of fixing the control system next to the lock), to which the output of the control system will be connected to the trunk lock in the future. The inductance of this pair is an important component of the input impedance of the slot (it was this value that was one of the know-how).
2. At the free end of the repeater, use a high-frequency bridge to measure the impedance, and design the control system for this value. In principle, you can do without measurements, simply by taking any customizable control system of the desired range and achieving a minimum SWR.
3. Make a fixed and small SU according to the data received, and install it at the trunk lock.

In the VHF band, depending on the frequency, the SU can have a variety of schemes. Unlike the HF band, in this case, careful individual adjustment to a specific type of vehicle and operating frequency is required. For example, at a frequency of 144 MHz, the SWR level band< 2 составляет 5...7 MHz.

Results

In both described ranges (meaning 27 MHz and 144 MHz), the following were noted:

1. The almost complete absence of influence on the parameters of the slot antenna of objects located in the passenger compartment (people, cargo) and around (precipitation, other cars, etc.);
2. Low level of electromagnetic field strength in the cabin (currents flow along the outer surface and, due to the surface effect, almost do not flow inside the cabin);
3. vertical (remember: horizontal slot, has vertical polarization), which works well with most car antennas that are also vertically polarized.

In the range in the horizontal plane, it is close to an ellipse with a small (about 3 dB) radiation maximum, backward along the vehicle axis. The communication range is the same as with a 20 cm high helical antenna or a 0.6 m high whip antenna with an inductor coil, which were placed on the roof of the car.

In the range of 144 MHz, the RP in the horizontal plane depends on the type of car and the operating frequency and is a complex multi-lobe structure without deep dips with a small maximum of radiation back. The communication range is 35% ... 50% of the range when using l / 4 pins on the roof of the car.

The worst parameters are explained by the location of the antenna feed points closer to the ground and the poor conductivity of the body iron in this range. For 144 MHz, the body iron is a very poor conductor - therefore, with large gap sizes in wavelengths, the efficiency is low. However, if you have a galvanized or tinned body, then the efficiency of the slot antenna will increase markedly.

Using the described principles, with an appropriate choice of connection points to the body and the control system circuit, it is possible to ensure the operation of a car body of any brand as a resonant antenna at any point of 20 ... 200 MHz. Of course, the effectiveness of such an antenna is inferior to a pin on the roof, but in cases where the concealment of the antenna is important, the body is the best solution.

The outdoor car antenna of most popular cars often breaks down, gets damaged. There are frequent cases of theft or vandalism in the yard parking of the car. Finding a factory antenna is problematic, automakers rarely release simple devices as spare parts. If a receiving device is broken or stolen on your outdated car, there is often no other way out than to make an antenna for your car radio with your own hands. Most drivers prefer to listen to FM radio broadcasts, which do not require long flexible or telescopic antennas for stable reception.

General principles of car antenna operation

Making an antenna for a car radio with your own hands at home is quite simple. But before manufacturing, you need to decide on the main parameters - the length of the antenna, its location, and the complexity of the design.

According to the postulates of radio engineering, a car antenna is defined as a quarter-wave vibrator grounded to the car body. Antennas for car transmitting radio stations are up to two and a half meters long and must work in a vertical position. For receivers of standard car radios, such parameters are redundant.

For stable reception of radio signals in the most popular VHF FM band, where most stations for motorists operate, a whip antenna 10 - 20 centimeters long is enough. An outdoor antenna for a car radio with your own hands will be the easiest way out when replacing outdated head units, designed only to receive long and medium waves.

Without considering antennas for receiving television signals, Wi-Fi Internet radio waves, let's focus on simple car antennas, which are divided into external and internal. Internal antennas shielded by the car body have weaker radio wave reception. For their stable operation, additional reinforcement or a complex frame structure is required. Only a trained radio amateur can independently calculate and manufacture a high-quality internal antenna, it makes no sense for novice tuning enthusiasts to take on such a design.

The process of making a homemade antenna

Flexible and telescopic antennas for manufacturing require the selection of special antenna materials, additional radio components. Plus, they break just as easily as your car's previous antennas.

A stationary solid antenna is easy to manufacture, imitating the fashionable shark fin receiver. To make such a homemade antenna for a car radio with your own hands, you will need simple materials and tools:

• metal pin with thread;
• fixing nuts;
• copper wire;
• metal tools;
• soldering iron and accessories for soldering (flux, solder, rosin);
• insulators;
• antenna cable.

The main element of the antenna is a metal pin, the thread of which is selected according to the size of the regular place of the antenna or the mounting bracket you have chosen. Standard pre-threaded anchor bolts work well for the base of the antenna. At opposite ends of the pin, you need to drill two holes for attaching the copper wire of the antenna vibrator. Unshielded wire is wound in two layers along the entire length of the pin.

The wound wire is clamped with fixing bolts and soldered in the upper hole of the antenna. For the outer layer of insulation, amateurs use various materials: cold welding glue, epoxy resin, polymorphus, thermoplastics. Melted vinyl and carbon fibre, which interferes with radio reception, has proven itself poorly.

After hand-molding thermoplastic or "epoxy", the antenna will look nondescript.

Having tried on the antenna at the installation site, having checked its performance, the outer surface is machined on a lathe and adjusted manually.

Depending on the color of the material used, the finished antenna can be left black or painted with waterproof acrylic paint in body color.

How to make an antenna for a car radio with your own hands for field trips, you can watch the video:

Connecting an outdoor antenna

The easiest way to install an antenna is for owners of cars that have a regular place on the body for installing a receiving device. In such models, it is enough to carefully screw the antenna into the existing connector (usually screw), without having to worry about laying the internal cable.

A well-crafted homemade rooftop antenna looks just as good as the fancy shark fin antennas found on expensive Mercedes, Audis and BMWs.

In the absence of a regular place on the car body, a do-it-yourself home-made antenna for a car radio can be installed on magnetic brackets or vacuum suction cups. It is preferable to use magnetic holders, which are more firmly held on the roof of the car in motion.

It is undesirable to make extra cuts in the car body, so you can use existing technological holes or expand the grooves of the rear light seals as little as possible. All cable outlets to the body must be sealed with sealant. Remote magnetic brackets for taxi drivers' walkie-talkies are well suited for rework. In this design, you only need to remove the extension coil (stands at the base of the antenna) and connect the cable directly to the pin. Theoretically, the best place to install the antenna is considered to be the center of the roof, but usually motorists install a homemade device on the left fender or at the back of the roof.

To connect an outdoor antenna, you must use a coaxial shielded cable. To lay the cable inside the cabin, you will need:

1. Remove the interior trim from the cable entry point to the center panel. All operations must be carried out carefully, without the use of brute force, keeping the plastic clips of the fasteners.
2. Lay and secure the cable. It is advisable to avoid intersections with standard electrical wiring that cause additional radio interference.
3. Compare antenna and head unit connectors. If necessary, solder the antenna connector or use an adapter.
4. Check the operation of the car radio receiver.
5. Collect the removed interior elements.

With the correct assembly of the antenna, cable laying, the new receiving device will work no worse than the standard antenna.

Conclusion

Having worked on the appearance of the receiving device, you will avoid claims from traffic police inspectors who may find fault with a sloppy homemade antenna. By sending us your feedback about your own experience in making antennas yourself, you will help fellow motorists avoid common mistakes.

Car antennas are different. They are mainly used to receive FM radio stations or to watch TV programs on mini-devices equipped with a special tuner. In addition, antennas in the car are needed as a navigation channel. In military conditions, car antennas are necessary to receive the signal.

Today we will talk about how to make a radio antenna in a car in order to listen to FM radio stations, how not to make a mistake when purchasing a finished device, and you will also find out what types of car antennas exist.

Classification of car antennas

If you want to make a radio antenna with your own hands, then this is not a big deal for you, since such a device has a fairly simple design. The main thing at work is to do it right select the wavelength(most often FM is chosen) and the type of modulation. However, we will return to this later, but now let's find out what categories car antennas are divided into.

According to their purpose, they are adapted to receive:

• broadcasting in different bands, mainly FM;
• television broadcasting;
• information from the satellite in order to ensure the operation of navigation systems.

There are also communication antennas.

Installing the instrument on the car can be carried out:

• with the help of magnets;
• through suction cups;
• mortise method;
• threaded connection method;
• clamp;
• embedded method.

According to the method of placement, antennas can be outdoor and salon, and according to the type of amplification - active and passive.

There are a number of other classifications, but they are too specific, so we will not dwell on them.

The value of the instrument depends on the range. For example, a 27 MHz communications antenna is large. The most powerful specimens can have a length of about 2 meters.

To work properly, install the antenna on the car in a strictly vertical position, which is determined by the type of polarization. Of course, connected structures can be tilted with a lever or lamb so as not to break in certain places, but they are mainly used by drivers of large vehicles.

A digital television antenna for a car looks like a flasher on a police car, only it has a different shade. The device of this design is quite simple, its main task is hundreds of MHz reception. Most often, a digital installation is placed on the roof of the car using a magnet, while the wire is pulled over the door without additional modifications. The signal is horizontally polarized.

What to look for when buying

Antennas for car radios are also small, but they are slightly larger than televisions because the wavelength is higher. For this purpose, pins of small height are suitable, resembling devices for receiving radio signals, but their length will be less than that of police flashing lights. In order not to accidentally buy an antenna for a TV receiver instead of a special model for the radio, check out its specifications:

• the antenna for the radio receiver is designated as FM or AM (frequencies 70-108 MHz);
• for television - DVB - T (frequency up to 900 MHz);
• for navigation - GPS (400 MHz);
• for radio communications - CB (27 MHz).

Also remember to pay attention to antenna connectors. Most often, they should match your device, but it won’t hurt to check this before buying. It is believed that an external type car antenna catches better, but this only applies to work in urban areas. However, devices for installation inside the car interior are simpler in terms of installation, but at the same time they are cheaper, respectively, and will work worse than external ones.

To date, on sale you can find all kinds of hybrid products that can be used for all of the above needs - and watching programs and listening to FM radio stations, and navigation. There are also models with the function of switching reception from highway to city and vice versa. Such techniques differ from each other in sensitivity and features of interference suppression. So, on the highway, the reception range can increase up to 80 km.

Common tandem models, equipped with a pair of pins, one of which is designed for watching TV programs, and the second for listening to radio programs. Of course, in order to use such devices for their intended purpose, you will need special equipment.

How to make your own radio antenna

In assembling an antenna for listening to FM radio stations, the main difficulty lies in the constant vibration of the car body. Therefore, simple household antennas for terrestrial use will not work here and will have dead spots in terms of reception. For a conventional ground device, it is exactly the same from which side the signal will be given, but for one that is constantly in motion, a special approach to DIY assembly is required.

A properly hand-assembled car antenna should have such characteristics:

• not cause unnecessary questions from the representatives of the traffic police due to unnecessary refinement of the hull;
• must get up in the cabin;
• ensure reliable reception;
• have high efficiency.

Simple quarter wave vibrator in this case, it is not suitable due to its shortcomings:

• it is difficult in terms of manufacturing;
• relatively large;
• difficult to mount;
• may interfere with movement.

The best option for a passenger car is obtained from a frame structure, which should be laid directly under the rear window seal. It should be slightly narrowed upwards, in its center there is a capacitor that tunes the antenna into resonance on a particular channel. There are two receiving frequencies, it can be 27 and 65 MHz or 28.2 and 68, respectively.

The upper resonance should correspond to the lower range of the radio broadcast. That's why perform the following actions:

Now that the job is done, you can connect the antenna through the connector used by communication equipment. The cable must not be too long. The antenna is passive, so the signal can be strongly attenuated in the path. If you install communication equipment near the rear window, it will be better.

Benefits of a DIY Antenna

Homemade antenna has a number of advantages in comparison with the factory model. Of course, they will not have a long range and excellent reception, as you would like. But you can fit it to your car and not have problems with too high a height, which often prevents you from driving normally in hard-to-reach places.

In addition, you will not need to wind the matching device, and this is an extremely difficult job. Since you need to accurately maintain the number and pitch of turns, as well as select the wire of the desired thickness. In addition, all this requires sealing, which will result in you purchasing a number of accessories in addition to the antenna itself.

Capacitor for homemade design necessary due to the shortened contour. The coefficient is 0.3 in this case. The electrical lengthening of the frame is carried out by the middle loops up to the desired size, while the capacitor dampens the reactance to match the cable, allowing you to tune everything into resonance. Since the antenna is broadband, it can almost in any case be installed on the rear window of every car model without any major modifications. The setting should be made by minimum standing wave ratio.

Many car enthusiasts have long learned that sometimes purchasing and installing a factory antenna for a car is not only more expensive, but also difficult to install, unlike a homemade one. Yes, and the reception quality is sometimes worse than that of the "homemade". Therefore, if you want to please yourself with the melodies of songs on your favorite FM stations while driving, try your hand and make the device yourself. As you can see, it's not as difficult as it might seem.