There are places where television signal comes in very low quality. In such cases, you have to use an external antenna, on the vibrator of which the antenna amplifier is located. It allows you to strengthen the signal even at a distance of 100 km from the tower.

Widely used amplifiers are SWA amplifiers. They have low price and provide sufficient reliability. They have different gains and are designed for different ranges of channels. In the decimeter range, the gain is 34-43 dB and 10-15 dB in the meter range. In the photo below you can see the amplifier model SWA-555/LUX.

The SWA signal amplifier operates from a constant 12 V power supply. There is a circuit that allows voltage to be supplied to the amplifier via a coaxial cable along with the signal. On the market you can find an adapter that is also a power supply that solves the problem. It is shown in the photo below.

Connecting the adapter does not require any skill. We insert the wire that goes to the TV into one coaxial cable, and the antenna wire into the other. The adapter is installed into the outlet. It is not possible to mix up the wires, since there are different connectors at their ends.

Opening the power supply with adapter, you can find power transformer, simple and electrolytic capacitors, 4 diodes, a choke, a microcircuit that acts as a voltage stabilizer.

Everything except the transformer is located on printed circuit board.

Electrical circuit diagram of the power supply with adapter

The adapter shown in the photo above is assembled according to the classical scheme. AC voltage The 220 V network is supplied to T1 (transformer), which in turn reduces it to 12 V - 15 V. VD1-VD4 (diode bridge) will perform the function of a voltage rectifier. To smooth out ripples, capacitor C1 is used. After which a constant voltage is obtained, the value of which is about 16 V. Then it goes to DA1 (integrated stabilizer).

An LC filter is made on elements C3, L1. It is installed at the receiver input. It eliminates the loss of DC voltage and loss of video signal.

L1 (choke) prevents the high-frequency signal from flowing into the power supply circuit. At the same time, direct current flows freely to the central core of the TV cable, which comes from the amplifier. C3 (capacitor) prevents DC current from flowing from the power source to the TV input. There is no signal loss in this case.

To make your own power supply, you can use parts various types. Any transformer can be used with an output voltage of 15-18 V. This is due to the fact that the antenna amplifier does not exceed a current consumption of more than 2 W and 150 mA. As a choke, you can use a piece of dielectric, for example textolite, the width of which is 5 mm. 25 to 30 turns of enameled copper wire are wound around it.

Disadvantages of the presented design of the power supply with adapter

One of the disadvantages is the presence of a section that does not have a screen on the central core of the television cable. This section is located at the soldering point with printed circuit board. When operating equipment such as a vacuum cleaner, this may cause interference to the video signal. This can be avoided by installing an additional screen.

Making your own adapter

If you need an adapter - an adapter that has wide technical capabilities, you can make it at home from a crab antenna splitter. To power the amplifier and additionally connect several TVs to the antenna, the crab circuit will have to be supplemented with 3 parts.

Design and diagram of the crab

The TV crab is metal case, having F – connectors. High-frequency transformers for the TV signal splitter are wired inside it. They are located on the central terminals. The high-frequency transformer looks like a tube or ring made of ferrite. It has a magnetic permeability of 600-2000. Turns of enameled wire are wound on top, the diameter of which is 0.2 mm–0.3 mm. They are located evenly around the entire circumference. The number of such turns can reach from 1 to 10.

The photo shows a crab. The back cover has been removed. As you can see, the ferrite transformers are wired in order to connect 3 TVs. It was manufactured according to the electrical circuit diagram shown below.

All crabs are made according to this pattern. It may have some deviations - installed chokes, resistors, filtering, decoupling capacitors.

How to make your own adapter
for supplying supply voltage to the antenna amplifier

In order to make an adapter designed to supply voltage to the antenna amplifier, I did not install a connector under the power supply. I decided to use one connector to connect the F-plug. To do this, it was necessary to remove one transformer. The number of connected TVs has decreased to two.

As a result, the concept has undergone changes.

Before using the adapter for its intended purpose, you should install the LC filter in the crab. The body of the crab is made of duralumin, so I made a brass terminal. It was secured to the body using a screw and a shaped nut.

As a result, the scheme changed slightly. Transformer T1 remained in its place, 2 capacitors and a choke were added.

To match the circuit, it is advisable to install a 150 Ohm resistor between the output pins XW3 and XW2. The adapter can be installed in any convenient location. Both at the cable entrance to the apartment and near the TV.

If you only use one TV, T1 can be removed from the circuit. Solder the right pin C1 (capacitor) to the central pin of connector XW3 or XW2. The cable will be connected to a connector to which a capacitor will be soldered.

Connecting the power supply to the adapter

I previously wrote that I want to connect the cable via the F connector. Therefore, from the double wire that came from the power supply, I made an adapter to a coaxial cable.

An antenna amplifier is a device that is installed on the antenna in order to strengthen the signal and, as a result, improve the quality of the picture on the TV screen. It will be especially relevant in areas far from television towers. As a rule, these are villages and villages located far from civilization.

Installing an antenna amplifier is necessary to improve signal quality.

There can be many reasons for poor signal reception. Even residents of large cities face this problem, although it would seem that they are in close proximity to the towers. The most common causes of interference:

• the signal source is too far from the receiving point;
• obstacles located in the signal path - trees, high-rise buildings, etc.;
• landscape gap between the signal reception point and the tower;
• weak signal.

The choice of antenna amplifier depends on many factors. However, the first thing you need to understand is what kind of antenna is installed. There are two types: passive and active. A signal amplifier is already built into the active antenna design by default. If you have problems with the signal, then most likely you are the owner of a passive antenna. Such an antenna should be installed only if the tower transmitting the signal is within sight and there are no obstacles between it and the antenna.

The next thing you need to find out is the distance to the nearest tower.

ADVICE. Depending on the distance to the tower, you should select a device with a suitable gain. As a rule, it is worth buying an antenna amplifier only if the distance from the tower to the house is more than 10 km. If the distance is shorter, then the problem is in an incorrectly selected antenna and the position amplifier will not correct it.

Gain is a characteristic that you need to be careful with. This is a case where more is not better. If there is a deficiency, the signal will not be strong enough, and if there is an excess, noise will appear, which will still interfere with high-quality broadcasting. For this reason, many amplifier models with different characteristics are produced for one type of antenna.

For the right choice coefficient, you must use a special table. There's nothing complicated about it.

Types of amplifiers

We will not go into the intricacies of the design of the antenna amplifier - for the average person this information will be useless. Let's talk about two types of amplifiers and their purpose.

Amplifier SWA

SWA antenna amplifiers are used in ASP-4 and ASP-8 array antennas, which are often called “Polish” antennas. These antennas themselves have a very low gain, and they cannot do without an amplifier.

The two most important characteristics when choosing an SWA amplifier will be gain and noise figure. When purchasing, pay attention to them. We have already talked about the first above. With the second it is still simpler - the less, the better.

Amplifier LSA

This type of amplifier has a very narrow field of application. They are produced for repairing failed Locus antennas. Certain LSA models can enhance their corresponding Locus antenna models.

power unit

As a rule, the antenna amplifier design is equipped with a built-in power supply. The device connects to the network and, due to its low power, consumes only about 10 W. There are built-in and external power supplies. Integrated power supplies are low-power, small-sized devices. If the electrical network is unstable, they are of little use. However, if power surges are very rare, it will be quite sufficient.

External power supplies are characterized by large dimensions and power consumption. They provide stable operation of the antenna amplifier even in unstable network conditions. Such power supplies are designed for different input voltages: 5, 12, 18, 24 V. This parameter must exactly match the supply voltage of your specific amplifier.

Antenna amplifier installation

Externally, the amplifier is a small electronic circuit. It is attached directly to the antenna itself using bolts and nuts. The amplifier will show greater efficiency if it is installed near the antenna on the mast, between the matching device and the feeder. The signal passing from the antenna through the feeder significantly reduces its level. After installation, you need to check whether the signal has improved. Without equipment, this can be done by simply turning on the TV.

If the antenna is already installed, it will not be difficult to connect the amplifier and, using a special adapter, power the power supply. However, if the antenna is not connected, then you will have to worry about running the cable to the TV. If you are not confident in yourself, then the best solution will call a telemaster who will quickly and efficiently complete this task.

Connecting a TV cable to your TV

The first step is to select a television cable. This is a very important moment, since even an expensive TV will not provide you with a high-quality picture without the right cable.

The most common on the market are coaxial cables from various manufacturers with a characteristic impedance of 75 Ohms, brands RG 6U, SAT 50, SAT 703B and DG 113. Brands are listed in ascending order of quality. Marking is applied to the cable sheath along its entire length.

IMPORTANT. We will not describe all existing antenna cables, since this is not possible. However, please pay your attention to the following - the cable must have a characteristic impedance of 75 Ohms and the outer diameter of the sheath must be at least 6 mm. Adhering to these two criteria, you can choose the right cable.

After you have chosen a cable, it must be connected to a plug, since bare wires cannot be connected to the TV. Nowadays, F-plugs are the most widely used. Plugs available three different sizes for cables of different diameters. Be careful when purchasing - make sure the plug fits your cable. After purchase, all that remains is to install the plug. This can be done according to the diagram below.

Antenna Grounding

However, that's not all. The antenna must be grounded before use. This is a very important and responsible procedure, and it should be approached with all responsibility.

IMPORTANT. Be careful! In the previous stages, the most you could ruin was the cable. When grounded, there is every chance of getting an electric shock - which can be fatal. Therefore, under no circumstances try to do grounding yourself! Call a specialist who will do everything quickly and efficiently.

If you live in an apartment building, as a rule, the antenna will be installed on a balcony or loggia. In such cases, there is no need for grounding, since it is already provided for when the house was built. Grounding will be relevant in a private house or on a summer cottage.

That's all. In this article we talked about the existing types of antenna amplifiers and how best to install them. We hope the article was informative and helped you in this difficult issue.

Broadband antenna amplifier SWA- 555/LUX Eurosky installed in external antennas, grilles, meshes, or as they also say (Polish antennas), to amplify the TV signal. Depending on the distance to the telecentre, various models, having different gain coefficients and allowing you to receive television programs at a distance from 0 to 150 km from the television center. Broadband antenna amplifiers S.W.A. have input impedance, determined by the antenna design 300 Ohm, output impedance 75 Ohm, use a supply voltage from 9 V to 15 V and are designed to amplify the frequency range 49 MHz - 790 MHz. Voltage is supplied to broadband amplifiers using adapters that differ only in the design of the housing and the output voltage is 12V. Broadband antenna amplifiers S.W.A. designed to increase the signal level and compensate for losses in transmission lines. Such amplifiers are produced using SMD technology using the most modern low-noise transistors, which are manufactured by leading foreign companies - ITT, Siemens, Philips, etc. They can be used in various designs of broadband antennas. Thanks to fully automated multiple monitoring, wideband amplifiers have good reliability, and thanks to the protective coating, they are resistant to atmospheric agents.

Currently, the largest range consists of broadband antenna amplifiers SWA, WS, RA, RAE, GPS, etc. They have different circuit designs, which allows, through simple selection, to achieve the required results in areas with different levels of received signal. In areas with a relatively good level of received signal, amplifiers with one amplification stage (single-stage) SWA-1, SWA-1 /LUX, PA-2, S&A-110 are usually used. In areas with insufficient received signal level, use two-stage (two-stage) amplifiers WS-2, SWA-3, SWA-4/LUX, SWA-5 (SWA-6), SWA-7, SWA-8, SWA-9, PA- 5, S&A-130, PA-9, S&A-140, PA-10, S&A-120, PAE-14, PAE-42, PAE-43, PAE-44, PAE-45, PAE-65, PAE-65TS, WA-031, WA-032, WA-041, WA-042, WA501S-1.

The table shows the technical parameters and characteristics of antenna amplifiers S.W.A. and their analogues pa, gps, pae. The noise figure and gain are given in dB, the recommended distance to the telecentre is given in km.

Price for broadband antenna amplifier SWA-555/LUX Eurosky

Location of T2 transmitters in Ukraine.

The table provides information:

• Locations of T2 transmitters.
• average signal coverage radius.
• numbers of television channels of digital packages (multiplexes).

Digital television of the DVB-T2 standard in Ukraine.

Until June 17, 2015, in accordance with the international agreement (Geneva 2006), Ukraine is obliged to switch completely to digital broadcasting of the DVB-T standard and DVB-T2. This is the plan for the development of the national television and radio information space. Now our country is beginning to gradually switch off broadcasting in analogue format. For quite a long time in Ukraine they have been broadcasting in test mode DVB-T and DVB-T2 digital standards. Standard DVB-T2 becomes basic for broadcasting and development digital television in Ukraine.

DVB-T2 This is the second generation European terrestrial standard for digital terrestrial television. Ether is a hypothetical all-pervasive medium (the upper layer of air). Unlike the first generation DVB-T standard, the standard DVB-T2 designed to increase network capacity by 30-50% while preserving core infrastructure and frequency resources.

In addition, among the benefits of switching to DVB-T2 the following can be distinguished:

• increasing the number of channels in the broadcast package.
• possibility of organizing regional (local) broadcasting.
• possibility of developing high definition television.
• release of ethereal frequencies.
• Available in all corners of Ukraine (covers 95% of the territory)
• Very easy to connect
• Excellent picture and sound quality
• All popular national TV channels are available
• Provided without subscription fee

Digital TV format DVB-T2- the most modern of all existing today, which, of course, the whole world will come to in the near future, since its capabilities are much wider than those of standard DVB-T. The main and undeniable advantage of the technology DVB-T2 is that its functionality is not limited to broadcasting free digital TV channels. In addition to watching 32 digital TV channels in highest quality, in the near future it will be possible to record your favorite programs for delayed viewing, order movies from network servers, watch online television, and listen to digital radio. IN DVB-T2 the possibility of transmitting several independent traffic flows of different nature and structure is incorporated. Each digital stream is placed in its own main stream - the so-called channel physical level PLP. For this purpose, a function has been introduced pre-treatment input data. Standard DVB-T2 fundamentally different in both system level architecture and physical layer properties, as a result of which DVB-T receivers are incompatible with DVB-T2.

DVB-T2 characteristics:

• OFDM modulation with OPSK, 16-QAM, 64-QAM or 256-QAM groups.
• OFDM modes 1k, 2k, 4k, 8k, 16k, 32k and “32k ext”. The symbol length for 32k mode is about 4ms.
• Relative lengths of guard intervals: 1/128, 1/32, 1/16, 19/256, 1/8, 19/128 and 1/4. (For 32k mode maximum 1/8).
• Forward error correction (FEC) with cascaded application of LDPC and BCH correction codes (as in DVB-S2 and DVB-C2).
• DVB-T2 supports channel frequency bands: 1.7, 5, 6, 7, 8 and 10 MHz. Moreover, 1.7 MHz is intended for mobile television.
  
• transmission in MISO mode using the Alamouti circuit, that is, the receiver processes the signal from two transmitting antennas.

DVB-T2 service capabilities:

• Multichannel multiplexing.
• Standard definition television SDTV in screen formats 4:3 and 16:9.
• Standard definition television HDTV.
• Ultra high definition television UHDTV.
• 3D television in the DVB 3D-TV standard.
• Interactive hybrid television in the Hbb TV standard.
  
• Video on demand.
• Teletext.
• TV guide.
• Subtitles.
• Stereo sound.
• Dolby Digital sound.
• Surround sound.
• Multisound (choice of broadcast language).
• Digital radio.
• Synchronize time and date with digital television broadcasts.
• Data transmission in the DVB-DATA standard.
• Direct and return channels communications for interactive services in the DVB-RCS and DVB-RCT standards.
• Broadband Internet access.
• Notification system.

Reception of DVB-T2 digital signal:

Reception of the digital signal is carried out by an on-air collective or individual (outdoor or indoor) television antenna, UHF, connected to various receivers:

• LCD/LED TV with built-in DVB-T2 tuner.
• TV set-top box (receiver, tuner, receiver) DVB-T2.
• DVB-T2 TV tuner for computer.

Advantage of digital signal DVB-T2 consists in the fact that a digital television signal is received by a UHF antenna and transmitted without distortion, as a result of which the stability of image and sound on TV receivers increases. Another advantage is the absence of image interference associated with atmospheric phenomena. Digital signal is protected from this, and on the TV screen you see a very good quality. In addition to high-quality pictures, you get five-channel sound. Plus, you receive additional information EPG (electronic TV program) - provides information about the current program, and a TV guide for 7 days. The broadcast is broadcast in multi-channel networks consisting of five multiplexes, these include: 32 standard channels DVB-T2(MPEG-4), taking into account 28 national and 4 regional television channels. Further plans include a significant expansion of the number of television channels through paid channels; one way or another, 32 channels remain available without any subscription fee.

Now in digital standard DVB-T2 in Ukraine, 32 TV channels are available to viewers .

* TV channels whose broadcasts are planned to be transferred to high definition format ( HD).

** Regional TV channels: differ depending on the region and the specific region.

The price of equipment for viewing in the DVB-T2 standard

Antenna designs

A. PAKHOMOV, Ph.D. tech. Sciences, Zernograd, Rostov region.
Radio Magazine, 2000, No. 7

The author has already talked about SWA antenna amplifiers for Polish small-sized television antennas (as they are popularly called “Grid”) (in more detail in the material SWA Amplifiers for “Grid” antennas). Over the past time, many new models have appeared on the Russian market. This article introduces readers to their circuitry and characteristics.

In the 90s, due to the expansion of the on-air television broadcasting network and the increase in the number of operating channels, user interest in multi-channel television antennas, capable of receiving programs in the MB and UHF bands without any switching, sharply increased. Since the middle of the decade, Polish small-sized TV antennas ASP-4WA, ASP-8WA (CX-8WA) from ANPREL, DIPOL, ELECTRONICS, etc., satisfying (to one degree or another) the requirements of such a reception. The antennas quickly gained popularity, and a fairly large number of them are now in use.

Individual television antennas ASP-4WA, ASP-8WA are flat vibrator structures with a common mesh reflector screen. They are active, that is, they are equipped with electronic amplifiers installed directly on the antennas and fed through a reduction feeder. Many characteristics of antennas, such as gain and bandwidth in particular, are obtained through the use of antenna amplifiers. Consequently, the quality of the reproduced television image largely depends on the parameters of the latter.

For active ASP antennas, different manufacturers produce a whole range of unified antenna amplifiers under different trademarks and numbers. Structurally, they are all designed the same: in the form of a small printed circuit board (approximately 60x40 mm) with surface-mounted microelements. The boards are made according to automated technology SMD and are quite reliable, thanks to repeated testing. Due to their characteristic design, these antenna amplifiers are called plate amplifiers.

The circuit design, parameters, shortcomings and repair of a large number of SWA antenna amplifiers are described in detail in. However, companies producing such amplifiers are improving their products, and many new models have now appeared: SWA. S&A, GPS, PAE, etc. Their parameters are undoubtedly of great practical interest both for owners who are already using antennas and want to improve image quality, and for those who have decided to buy a new antenna. In addition, amplifiers can work with other types of antennas, for example, log-periodic, wave channel, etc. (subject to matching input impedances).

Antenna amplifiers have a number of characteristic parameters, which can be divided into two groups: general and individual. Common ones include: input and output resistance(300 and 75 Ohms, respectively), supply voltage (9... 15 V at a nominal 12V), operating range of frequency channels (1-68 TV channels, with rare exceptions). Thanks to the common parameters, the interchangeability of amplifiers is ensured.

However, to assess the quality of an amplifier, individual parameters that distinguish one amplifier from another are also important, in particular, noise and gain. Information about them is not always available, although Lately it began to be partially included in the sales documentation for antennas. It is fully listed in company catalogs, which are difficult to purchase even from companies that sell antennas wholesale.

In order to correctly select an antenna amplifier, you must know its two individual parameters: noise figure and reduced gain Ku. It is also highly desirable to imagine the type of its frequency response.

Of primary importance when choosing an amplifier is the noise figure: it should be as small as possible and certainly lower than that of the TV input stage. A modern antenna amplifier should have a noise figure of no more than 2 dB.

The second parameter (gain) is calculated using the method described in, based on signal losses in the cable and passive splitters (if any). The antenna amplifier is selected according to the coefficient Ku closest to the calculated value. Increasing it above the calculated one has an effect while simultaneously reducing the noise level, otherwise the danger of self-excitation and overload of the amplifier with powerful signals from nearby stations only increases.

It is also necessary to take into account the dependence of the coefficient Ku on the frequency, which is determined by the real frequency response of the amplifiers. Each of them has its own characteristic type of frequency response. Thus, the SWA and PAE amplifiers have one smooth maximum (hump) at a frequency of approximately 600 MHz (the gain rise reaches 6... 10 dB). The S&A and RA amplifiers have a double-humped characteristic: the second gain increase of 3...5 dB is located at a frequency of approximately 100 MHz, i.e. at MB. The type of frequency response allows you to select an amplifier depending on the reception conditions in order to improve stability and noise immunity by reducing the gain in non-operating sections of the range. The gain indicated in the documentation, as a rule, refers to the DM V range; at MB frequencies it can be significantly lower.

Most of the new amplifiers are assembled according to the traditional two-stage OE-OE circuit. Let's consider the circuit design, parameters and frequency response of some new models of amplifiers of various brands.

Amplifier SWA-555, the circuit diagram of which is shown in Fig. 1, is a two-stage aperiodic RF amplifier based on T67 (BFG-67) or BFR-91A bipolar microtransistors. The first stage is broadband, without correction. In the second stage there is a correction: capacitor C5 in the current feedback circuit of transistor VT2 ensures a decrease in the frequency response at lower frequencies of the operating range, and capacitor C4 in the voltage feedback circuit limits the gain at higher frequencies and outside the operating band. The frequency response of the amplifier is shown in Fig. 2. In general, the circuits of the SWA-555 and SWA-9 amplifiers are almost completely identical (the former only lacks an LC filter in the power supply circuit and some values ​​of the passive elements have been changed). Therefore, the frequency response of the amplifiers is close. However, when using a low-noise transistor BFR-91A (Ksh = 1.6 dB) in the first stage, the SWA-555 amplifier has a lower noise figure.

S&A amplifiers have more complex frequency equalization circuits in both stages. In models S&A-130, S&A-140, the circuit diagram of which is shown in Fig. 3, a series circuit L1C2 is introduced into the OOS circuit based on the cascade voltage on transistor VT1. His resonant frequency choose such that the gain of the first stage decreases at the upper frequencies of the range, which contributes to the stability of the amplifier. To expand the correction band, the quality factor of circuit L1C2 is reduced by resistors R1, R3. which provide the necessary constant base current of transistor VT1.

The second stage is equipped with double RC circuits R6, R7. C6 and R7. C4, C5 in the emitter circuit of transistor VT2, changing the frequency response in the low-frequency region. As a result, the characteristics of the amplifiers are double-humped, as shown in Fig. 4. The increase in gain at a frequency of 100 MHz reaches 3...4 dB. The gap between the humps occurs at frequencies of 230...400 MHz, not used broadcast channels television. This form of frequency response improves the stability and noise immunity of the amplifier.

Other features of the S&A amplifiers include the use of a VD1 lightning protection diode at the input. Its efficiency is not very high, so it is recommended to ground the antenna.

The PAE amplifiers, like the S&A, use LC correction in both stages. In the PAE-45 amplifier, the circuit diagram of which is shown in Fig. 5, it is provided by two serial circuits L1C3 and L2C5, connected in the OOS circuits according to the voltage of the first and second stages, respectively. In addition, capacitors C2 and C8 also influence the formation of the frequency response. As a result, the hump on the frequency response of this amplifier turns out to be sharper, with a sharp decline at frequencies above 700 MHz, as can be seen in Fig. 6.

There is no point in considering RA amplifiers in detail, since they are similar to S&A amplifiers, with the exception of using a VD1 coil at the input instead of a diode. The type of frequency response of the RA and S&A amplifiers is approximately the same.

The GPS models are similar to the SWA-455, SWA-555 amplifiers and differ only in the ratings of the correction elements in the second stage. By increasing the capacitance of the blocking capacitor in the emitter circuit of the second transistor, increased gain was achieved in the frequency range 100...400 MHz.

In some new amplifier models, an additional circuit of series-connected trimming and constant resistors and a capacitor is connected to the emitter of the second transistor (shown in Fig. 1 with a dashed line). In this case, a trimming resistor can be used to change the gain in the lower frequencies of the range and, consequently, the frequency response of the amplifier. Unfortunately, the value of such a correction regulator is small, since the amplifier is difficult to access when the antenna is raised.

The analysis of circuit design and frequency response, of course, is not complete, since, in addition to corrective circuits, the frequency response is affected by the relative position of parts, installation capacity, the presence of strip lines, etc. Nevertheless, in the author’s opinion, it is sufficient for the correct selection of an amplifier according to the type of frequency response, and in some cases for self-adjustment by selecting corrective elements.

The following practical recommendations emerge from the analysis. Real view The frequency response of the SWA and RAE amplifiers is such that they are best used mainly for receiving remote UHF stations. at which amplifiers have maximum gain. Due to the reduced gain in the MB region, such amplifiers (especially PAE) are more stable and better protected from interference at these frequencies.

To receive weak MB signals, preference should be given to S&A, RA and GPS amplifiers that have increased MB gain. This is especially important considering that small-sized ASP antennas have very little intrinsic gain in the MB band: at a frequency of 50 MHz, for example, the ASP-8WA antenna does not exceed 1 dB.

Main parameters of new SWA models. S&A. PA, GPS, PAE (operating frequency interval f, noise figure Ksh and gain Ku), taken from the Internet. as well as company catalogs, are presented in the table placed here. If there is a discrepancy in the information, the worst values ​​are added to it. It is obvious that some new models have achieved some reduction in noise (up to 1.5 dB), however, there are still quite “noisy” amplifiers with a noise factor equal to 3...3.9 dB (SWA-31. SWA-32, S&A- 110. S&A-120. RA-10), which are not recommended.

Manufacturers have not yet managed to achieve a significant improvement in the noise characteristics of most amplifiers. The best previous models SWA-7, SWA-9 had a coefficient of Ksh = 1.7 dB. It remained approximately the same for new amplifiers or was reduced slightly, with the exception of models SWA-47(AST), SWA-49(AST). This is explained primarily by the fact that the circuit design and the transistors used have not changed: the input stages use the same microwave transistors T67, V3, 415 with a maximum frequency of 7.5 GHz and a noise figure of up to 3 dB, and only occasionally the less “noisy” BFR- 91A.

It should be noted that the characteristics of the amplifiers are influenced not only by the type of the first transistor, but also by the operating mode. The level of its own noise, the gain and the value of the active component of the input conductivity, which affects the degree of input matching, depend on its collector current.

In most antenna amplifiers, transistor VT1 operates at a collector current of 1 “= 8...12 mA. This makes it possible to obtain a fairly high gain and good matching with the input transformer T1, but is not optimal for ensuring a low level of self-noise. Although the dependences Ksh=f(Ik) of the microchips used are unknown, as a rule, for bipolar silicon microwave transistors, the minimum noise level is observed at a collector current of 2...5 mA. Therefore, it is possible that by reducing the collector current of transistor VT1, the noise level can be reduced while maintaining good input matching. This is indirectly confirmed by the fact that for PAE amplifiers (only for them) the current of the first transistor is reduced to 4...5 mA. due to which, with the same transistors, a significant reduction in the noise level has been achieved: according to information from the Internet, the Ksh coefficient for these amplifiers reaches 0.8... 1 dB.

As noted in , many high gain SWA antenna amplifiers are prone to self-excitation. This is explained by this. that it is quite difficult to ensure the stability of a two-stage aperiodic RF amplifier assembled according to the OE-OE circuit in the frequency band up to 900 MHz. It would seem that further increasing the number of cascades does not make sense, since achieving stability in this case is almost impossible. Nevertheless, amplifiers based on four transistors have appeared on the market. Interested in this fact, the author purchased the SWA-2000/4T amplifier. Its circuit diagram, compiled from a printed circuit board, is shown in Fig. 7.

An analysis of the circuitry of this amplifier showed that it is assembled according to the usual circuit using two transistors VT1 and VT2 connected with the OE. The input signal is supplied to the base of transistor VT1, amplified in a two-stage tract and removed from the collector of transistor VT2. entering the coaxial cable through the transition capacitor C9. Additional transistors VT3 and VT4 are included in active circuits that set the bias voltage at the bases of transistors VT1 and VT2. Since transistors VT3, VT4 do not amplify the useful signal, low-frequency and cheap 3F chips are used for this purpose.

Obviously, with this design, the characteristics of the SWA-2000/4T amplifier cannot significantly exceed the parameters of two-stage amplifiers with similar correction (SWA-7, SWA-9, SWA-555, etc.), which was confirmed by comparative tests.

To summarize, we come to the following conclusions. Firstly, many of the new amplifiers repeat the circuit design and, accordingly, the characteristics of older models. At the same time, a solid number new development does not at all indicate its higher quality. For example, the SWA-555 amplifier in terms of parameters and circuit design is the same SWA-9 amplifier. The same applies to amplifiers assembled with four transistors.

Secondly, among the new amplifiers there are models with truly improved characteristics, which also suggests the possibility of improving reception quality. In terms of noise parameters, amplifiers SWA-47 (AST), SWA-49 (AST), and also, judging by information on the Internet, amplifiers of the PAE type can be considered the best.

Thirdly, replacing an antenna amplifier will lead to a positive effect only if a new model with a lower noise level, a calculated gain value and a suitable frequency response is used.

In conclusion, we will say that manufacturers are developing models of antenna amplifiers quite quickly and it is possible that by the time the magazine with this article is published, new, improved amplifiers will probably appear. In any case, the criteria for determining their quality and recommendations for selection, discussed here and in, do not change.

LITERATURE
1. Pakhomov A. Antenna amplifiers SWA. - Radio. 1999. No. 1. p. 10-12.
2. Nesterenko I. I., Zhuzhevich A. V. Choose the antenna yourself. - M.: Solon. 1998.
3. Semiconductor devices. Low power transistors. Directory (A. A. Zaitsev, A. I. Mirkin, V. V. Mokryakov, etc.). Under the general editorship. A. V. Golomedova. - M. Radio and communications, 1989.