DIY antenna amplifier: a master class on making a universal device with your own hands. Radio circuits electrical circuit diagrams Amplifier of decimeter channels

Despite the rapid development of cable and satellite TV, it is too early to write off terrestrial television broadcasting. But for a high-quality signal of the latter, you need to be in the coverage area. As you move away from the TV tower, the quality of the signal decreases and the amount of interference increases. In such cases, an antenna amplifier for a television receiver helps well. We propose to consider what this device is, the principle of operation, various modifications, as well as the possibility of creating a TV signal amplifier for a city apartment, country house or cottage.

What is an antenna amplifier and how does it work?

This is a device that allows you to amplify a certain range of television signals and reduce the level of interference to obtain the highest quality “picture”. In addition, such amplifiers are used to reduce cable losses. Typical block diagrams of such devices are shown below.

As can be seen from the presented diagrams, the incoming signal is processed by an external frequency filter, after which it is reduced by an attenuator to the required level. Next, the signal enters the unit for adjusting the level of the frequency response slope, the principle of operation of which is in many ways similar to an equalizer. And at the last stage, the signal is amplified, after which it is sent to the television receiver.

Varieties

Despite the variety of equipment of this type, amplifiers can be divided into the following types according to their functionality and range:

How to choose a good antenna with an amplifier?

To get the most out of your purchased equipment, you need to consider the following factors:

• Distance of the nearest television signal repeater. It is generally accepted that the maximum distance is 150 kilometers, but this is a highly averaged value, since much depends on both the type of terrain and the power of the television tower. For example, if you are in a lowland, you may not receive a reliable signal even from a nearby repeater. In this case, installing a mast under the antenna will help correct the situation.
• In what frequency range will the equipment operate? It must be taken into account that the characteristics of wide-band antennas are inferior to narrow-beam antennas. This suggests that for an area of ​​reliable reception, an “all-wave” is quite suitable; accordingly, to receive a signal from a remote repeater, it is better to prefer a design for a certain frequency range (MV, UHF, VHF). But here, too, it is necessary to take into account the features and nature of the terrain; for example, you can only get rid of the reflected signal with the help of a highly directional antenna.

Having decided on the antenna, we move on to choosing an amplifying device for it. The first thing you need to pay attention to is the gain (indicated in decibels). As a rule, at a distance of up to 10 kilometers from the repeater, there is no need for an amplifier.

It is necessary to pay attention that you should not get too carried away with the high value of this parameter, since at high power the device may be “excited”, and as a result of this, interference will appear, appearing in the form of “white snow” in the picture. Below is a table for SWA equipment, which shows the main characteristics for each model, as well as the relationship between gain and range to the signal source.

The second important characteristic is the noise level (indicated in decibels) produced by the device during operation. The lower this figure, the better.

Naturally, when choosing, it is necessary to take into account the type of antenna; it is allowed to install a broadband device on a narrow-band signal receiver, but not vice versa.

How to make an antenna amplifier with your own hands - step-by-step instructions

Here are several typical device circuits for amplifying a television signal, starting with the simplest one.

Designations:

• VT – chip MAX2633.
• R – 1 kOhm.
• Capacitors C 1, C 2 and C 3 – 1 nF.

The circuit is tangled from a DC source with a voltage of 2.8 to 5.2 volts. Distinctive features: low noise level (about 2 dB) and quite a decent gain, about 13 dB, which, if necessary, can be reduced by increasing the resistance R. The assembled circuit does not require adjustment. The above device has proven itself well when working with indoor antennas of television and radio receivers. On the Internet you can find a description of this circuit as broadband, which is not entirely true, based on the datasheet MAX2633 - intended for the VHF range.

Now let's look at typical transistor circuits that are truly broadband.

Designation:

• Transistor VT1 – KT368.
• Resistances: R1 -100 Ohm; R2 – 470 Ohm; R3 – 51 kOhm; R4 – 100 Ohm.

The scheme is also simple and does not require configuration. Gain and frequency characteristics depend on the transistor used. Devices of this type are characterized by a high gain and low frequency characteristics (which is corrected in emitter-coupled multi-vibrator circuits; if desired, they are not difficult to find, but they are more difficult to configure). Power is supplied from a 9 volt source.

The option with a transistor connected using a “common base” circuit has a lower gain, but a wider frequency range.

Designations:

• Transistor VT1 – KT315.
• Resistances: R1 -51 Ohm; R2 – 10 kOhm; R3 – 15 kOhm; R4 – 1 kOhm.
• Capacitances: C1- 1000 pF; C2 – 33 pF; C3 and C4 – 15 pF.

The inductor is wound on a ferrimagnetic ring, the permeability of which is 600N. For the meter range, it is necessary to make 300 turns; the wire used for this purpose is PEV Ø 0.1 mm.

You can achieve greater gain if you assemble the device on a two-stage circuit, an example of which is given below.

Designations:

• Transistors: VT1 and VT2 – GT311D.
• Resistances: R1 – 680 Ohm; R2 – 75 kOhm; R3 – 1 kOhm; R4 – 150 kOhm.
• Capacitances: C1, C2 and C4 – 100 pF; C3 – 6800 pF; C5 – 15 pF; C6 – 3.3 pF.
• Chokes: L1 – 100 µH; L2 – 25 µH, L3 – is a coil on a frameless base, 4 mm in diameter, 2.5 turns wound, PEV wire used 2 Ø 0.8 mm.

The circuit is powered from a 12-volt source; device configuration is not required.

Step-by-step assembly instructions will be common for all schemes:

• We purchase all the necessary electronic components.
• We prepare tools and consumables.
• We are manufacturing a printed circuit board, mounted assembly and the use of mounting panels is undesirable, since in this case the noise level will increase significantly.
• We solder all the elements.
• We check the assembled structure.
• We connect the antenna and television receiver to the assembled amplifier.

How to connect an antenna amplifier to a TV?

The most important point is that the antenna amplifiers for the TV should be located as close to it as possible. This is due to the fact that cable losses can significantly affect the picture quality. The requirement applies to both home-made designs and serial models, for example BBK or Terra. The only exception may be indoor antennas, which have a short cable length, but, as a rule, such devices are used in the reception area where there is no need for an amplifier.

Carefully read the connection manual that came with the device.

If connecting an amplifier does not bring results, check the antenna's directivity, as well as its waveform compliance.

All manipulations must be carried out only with de-energized equipment.

Do not connect the amplifier to an external antenna unless it is equipped with lightning protection. Actually, such a signal receiver cannot be used at all.

Long-distance television reception in the UHF range

Television broadcasting on decimeter waves (UHF) has become widespread both abroad and in our country. The UHF range (470-1270 MHz) covers 80 television channels (from 21 to 100) and has a low level of noise and interference, which allows for multi-program high-quality broadcasting. UHF television reception has a number of features:

1. UHF practically does not bend around the earth's surface and have low penetrating power, so the area of ​​reliable reception is limited to the direct line of sight between the transmitting and receiving antennas.

2. At the same time, the UHF is well reflected from the earth's surface and from the ionized layers of the atmosphere. This makes reception possible at a considerable distance (300-500 km) from the television center. At the same time, the passage of UHF is quite stable and does not have fading characteristic of meter waves (MB).

3. A characteristic feature of UHF is the so-called wave propagation, in which the signal can be received at a distance of up to several thousand km from the television center. It occurs over the sea surface on clear days in the spring and summer months.

4. UHF receiving antennas have significantly smaller geometric dimensions than MB antennas. At the same time, their effective area is small, and therefore the signal power supplied to the input of the television receiver is small.

5. The sensitivity of television receivers in the UHF range is significantly lower than in the MB range, which is due to the poor noise parameters of the UHF selector. Analysis of the listed features shows the fundamental possibility of long-range and ultra-long-range television reception in the UHF range and two main ways of its implementation. This is an increase in the efficiency of the antenna system and the real (noise-limited) sensitivity of the television receiver.

The possibilities of increasing the gain of UHF antennas in practice are limited by the complexity of their design and coordination with the feeder.

Increasing the sensitivity of a television receiver requires altering the UHF selector and usually does not give the desired results. The fact is that in the UHF range the signal attenuation in the cable is high, and when using antennas with low gain it is not possible to obtain a significant gain in the signal-to-noise ratio at the input of the television receiver.

The most optimal way is to use a structurally simple antenna with an amplifier located in close proximity to it. In this case, it is possible to simultaneously increase the efficiency of the antenna and the sensitivity of the television receiver without modifying it.

The antenna amplifier must have a high gain, low noise figure, and a wide range of operating temperatures. At the same time, it should be simple in design, assembled from available parts, easy to set up and not prone to self-excitation.

As a result of many years of theoretical and experimental research, we were able to create a circuit and design of a UHF amplifier that is optimal according to the listed requirements, which has no industrial or amateur analogues.

G. BORICHUK, V. BULYCH, V. SHELONIN, St. Petersburg

1. UHF antenna amplifier

1.1. Amplifier parameters and circuit

The amplifier has the following parameters:

Gain coefficient Ku and noise figure Fsh in the range
470-630 MHz (21-40 channels) - Ku ≥ 30 dB, Fsh ≤ 2.0 dB;
630-790 MHz (41-60 channels) - Ku ≥ 25 dB, Fsh ≤ 2.5 dB;
790-1270 MHz (61-100 channels) - Ku ≥ 15 dB, Fsh ≤ 3.5 dB.

Input and output impedance - 75 Ohm
- supply voltage - 9-12 V
- operating temperature range - (-30...+40) °C.

The amplifier circuit is shown in Fig. 1. It contains two cascades on transistors VT1 and VT2, connected according to a circuit with a common emitter. To obtain maximum gain, the emitters of the transistors are connected directly to the common wire. The loads of the cascades are broadband circuits L2, R2, L3, C4 and L4, R6, L5, C10, which ensure matching of their input and output impedances. Circuit L1, C1 is a high-pass filter (cutoff frequency 400 MHz), which is used to eliminate interference from MB band TV transmitters. Capacitors SZ, C5, C7, C8 are blocking. The amplifier is powered via a coaxial cable connecting it to the TV, through a low-pass filter L6, R8, C11. Directly in front of the TV, the UHF signal and the supply voltage are separated by filter C12, L7, C13.

Rice. 1. Electrical circuit diagram of the antenna amplifier and separate power filter

The DC modes of the transistors are set by resistors R1 and R5 so as to obtain the optimal values ​​of the collector currents I1 and I2 of transistors VT1 and VT2. Current I1 is selected from the condition of obtaining the minimum noise figure of the first stage, and I2 - from the condition of obtaining the maximum gain of the second stage.

Amplifier parts and design

All amplifier resistors are MLT-0.125. Capacitors C1, C2, C4-C7, C9, C10 - small-sized disk capacitors (types KD, KD-1, etc.); SZ, S8 and S11 - type KM-5b, KM-6, etc.

All amplifier coils are frameless. Coil L1 contains 2.75 turns of silver-plated wire with a diameter of 0.4-0.8 mm, its outer diameter is 4 mm, the interturn distance is 0.5 mm. Coils L2-L5 are the leads of resistors R2 and R5, wound on a mandrel with a diameter of 1.5 mm, so that the interturn distance is 0.5 mm, and contains 1.5 turns each. The directions of windings L2, L3 and L4, L5 must be the same (i.e., for example, L2 and L3 are a coil of 3 turns, in the gap of which resistor R2 is connected). Coil L6 contains 15-20 turns of enameled copper wire with a diameter of 0.3 mm, wound turn to turn on a mandrel with a diameter of 3 mm. Choke L7 is a standard type DM-0.1 with an inductance of more than 20 μH. Zener diode VD1 - any with a stabilization voltage of 5.5-7.5 V.

The amplifier can use microwave low-noise transistors with cutoff frequency fgr. more than 2 GHz. If the amplifier operates in the range of 21-60 channels, then transistors with fgr can be used. more than GHz, and if - only in the range of 21-40 channels, then - with fgr. more than 800 MHz. in this case, it is necessary to install a transistor with a lower noise figure in the first stage, and in the second - with a higher gain. In table The parameters of transistors that can be used in the amplifier are given. Transistors are arranged in order of worsening parameters.

Table

It is not recommended to use transistors KT372 due to their tendency to self-excitation and GT346 due to poor noise parameters. If pnp transistors are used, then it is necessary to change the polarity of the amplifier's power supply.

The amplifier is assembled on a printed circuit board made of foil fiberglass laminate with a thickness of 1-1.5 mm. A drawing of the printed circuit board and a diagram of the installation of parts on it are shown in Fig. 2. The board is designed to use transistors with planar leads (KT3132, KT3101, KT391, etc.), which are soldered directly to the contact pads on the foil side. However, it also allows the installation of transistors with a different pin arrangement (KT399, KT3128, etc.), but from the installation side, for which it is necessary to drill the corresponding holes in the board for the pins (see below).

Rice. 2. Amplifier wiring diagram

The transistor leads must have a minimum length, especially the emitter lead, which should not exceed 4 mm. The terminals of capacitors C4, C5, C7 and C10 should be no more than 4 mm, and capacitors C1, C2, C6 and C9 should be 4-6 mm (they are additional inductances included in the circuits). Some of the terminals of capacitors C1 and C2 are soldered into the board, while others are soldered directly to the central core of the input coaxial cable. Capacitors C6 and C9 are soldered at one end to the heads of resistors R2 and R6, cleared of paint. The other end of C6 is in the board, and C9 is soldered to the central core of the output coaxial cable. Capacitor C2 is soldered at one end to the board, and at the other end it is soldered to coil L1 at a distance of 3/4 of a turn from the top end according to the diagram. Resistors R3, R4, R7 and R8 are installed vertically.

The printed circuit board is placed in a rectangular sealed case, divided into 4 parts by shielding partitions (Fig. 2, 4). Drawings of the housing parts are shown in Fig. 3. It consists of a side wall 1, a sleeve 2, a partition 3, 4 and covers 5. Parts 1, 3, 4 and 5 are made of sheet brass (it is convenient to use a photo-glazing plate annealed over a gas burner), parts 2 are machined from a brass rod. Bushings 2 are designed so that the input and output of the amplifier are made of a 75-ohm coaxial cable with an outer insulation diameter of 4 mm. You can use another 75-ohm cable, but in this case it is necessary to change the diameters of bushings 2 and holes in the housing wall 1 accordingly.

Rice. 3. Amplifier housing parts

The power supply filter L7, C12, C13 is mounted in a separate box of any design, on which the input antenna socket and output antenna plug are installed.

The amplifier can be powered from any stabilized 9-12 V source, for example, from commercially available power supplies for transistor receivers BP9V, D2-15, etc.

You can also mount filter elements inside the TV next to the UHF antenna input, and use 12 V voltage from the UHF selector to power the amplifier.

Amplifier installation and configuration

The amplifier is assembled in the following sequence. Mount all elements on the board except resistors R1 and R5. If transistors with non-planar terminals are used, then holes are drilled in the board for them, and rectangular cutouts are made in partitions 4 (shown with a dashed line in Fig. 3). The partitions 3 and 4 are soldered into the board with the corresponding protrusions. The side wall of the housing 1 is bent and soldered. The bushing 2 is hermetically sealed into it. The input 7 and output 8 coaxial cables, 80 cm long, are inserted into the holes of the bushings, the braid is divided into 2 parts and soldered to the housing from the inside. The central core of the cables should protrude 3-4 mm into the housing. Insert the board into the case so that the edges of the partitions 3, 4 and the edge of the wall 1 lie in the same plane (Fig. 4), and solder the joints of the partitions between themselves and the case. In addition, the odd board is soldered to wall 1 at 10 points. The soldering locations are shown in Fig. 2 and fig. 4. Elements C1, L1 and C9, L6 are soldered to the central cores of the cables. Check the rice carefully. 1, 2 and 4 correct installation.

Rice. 4. Amplifier design

Next, the amplifier is configured. To do this, power is supplied to the amplifier via output cable 8. By measuring the voltage U1 on resistor R3 by selecting resistor R1, set the value of current I1 (I1 = U1/R3) in accordance with table. 1 for the transistor of the first stage. Solder the selected resistor R1 into the board. A similar procedure is performed for the second stage, measuring the voltage U2 across resistor R7 and setting the current I2 = U2/R7 in accordance with table. 1. Solder in resistor R5. In Fig. 1, the values ​​of R1 and R5 are approximate; in reality, they may differ significantly from those indicated. Check the absence of self-excitation of the amplifier. To do this, connect a voltmeter in parallel with R3 and touch the collector output of transistor VT1 with your finger. If the first stage is not excited, the voltmeter reading will not change. The second cascade is checked in the same way. Self-excitation can be eliminated (its presence is indicated by a sharp decrease in the transistor current when it is touched with a finger) only by replacing the transistor. It should be noted that the amplifier is not prone to self-excitation - out of several dozen amplifiers manufactured, only one, assembled on KT372A transistors, was excited. Check the current consumed by the amplifier, which should be equal to: I1 + I2 = 10 mA; if necessary, select resistor R8 so that the current through the zener diode VD1 is about 10 mA. The final operation is to seal the amplifier. To do this, covers 5 are soldered around the perimeter of the case, and the places where the coaxial cable is inserted are additionally coated with some kind of sealant, waterproof glue, etc. The amplifier is then attached to the antenna mast.

UHF antenna

As mentioned above, it makes no sense to achieve a very high gain of the UHF antenna, since this leads to unjustified complication of its design. However, you can’t count on long-range reception with an ineffective antenna either.

Experience in the design and use of UHF antennas shows that the simplest and at the same time very effective is the Z-antenna with a reflector. Its distinctive features are wide-bandwidth, high gain, good matching directly with a 75-ohm coaxial cable and non-critical dimensions.

The antenna design for 21-60 channels is shown in Fig. 5. If the antenna will be used in the range of 61-100 channels, then all its dimensions must be reduced by 1.5 times. The active canvas 1 of the antenna is made of aluminum strips and is fastened “overlapping” with screws and nuts. There must be reliable electrical contact at the points of contact of the plates. At match 6 (it can be metal or wood), the canvas is fixed with the help of support posts 2 at points C and D. Since these points have zero potential relative to the ground, the posts 2 can be metal. Cable 3 is connected to points A and B (the braid to one point, and the core to the other) and is laid along the fabric along the lower post 2 and along match 6 to amplifier 7. The cable is secured with wire clamps. The web 1 can itself be used as an antenna. Its gain is 6-8 dB. However, it is better to equip the canvas with a reflector.

Rice. 5. UHF antenna, a) antenna surface; b) antenna with a simple reflector; c) antenna with a complex reflector

The simplest reflector 4 (Fig. 5b) is a flat screen made of tubes or pieces of thick wire. The diameter of the reflector elements is not critical and can be 3-10mm. An antenna with a flat reflector has a gain of 8-10 dB. The gain factor can be increased to 15 dB (equivalent to a 40-element “wave channel” antenna) using a complex “dilapidated box” type reflector (Fig. 5c). The design of such a reflector can be very different, depending on your capabilities.

The spatial orientation of the antenna, shown in Fig. 5 corresponds to receiving signals with horizontal polarization. To receive vertically polarized signals, the blade and reflector must be rotated 90°.

The UHF amplifier is located in close proximity to the antenna (see Fig. 5). The amplifier input is connected to the antenna surface using the same cable that is embedded in the amplifier. The amplifier input cable is extended with a reduction cable. It is desirable that it be as large in diameter as possible (losses in the cable depend on this); a cable with a diameter of 4 mm can be used only if its length does not exceed 10 m.

Cable connections should be made “vetically”, so that the coaxial structure of the feeder is minimally disrupted.

If it is not possible to produce the antenna described, then the amplifier can be used with slightly worse results with industrial outdoor broadband UHF antennas, for example, type ATNG(V)-5.2.21-41 (trade name “GAMMA-1”).

Antenna installation is determined by what type of UHF transmission you are counting on. If it is necessary to receive reception directly outside the service area of ​​the television center (60-200 km), then the antenna should be installed so that in the direction of arrival of the signals there are no obstacles between it and the horizon line (houses, hills, etc.). If you are focusing on ultra-long-range reception with tropospheric or wave propagation (in this case, the signal comes “from the sky” at an angle of 5-10° to the horizon), then obstacles that are not very close are usually not an obstacle.

The practical result of taking UHF

In conclusion, a few words about the practical results of taking UHF. An antenna with an amplifier manufactured according to the attached description was used for several years in Odessa for regular reception of signals from the Chisinau television center (distance - 160 km). Outside the city, in the radio shadow zone for the MB television center, signals from low-power UHF repeaters located on the opposite side of the Odessa Bay (distance - 60-80 km) are confidently received. On clear days in the spring and summer months, the Bulgarian BT2 program from Varna (distance - 500 km) and the Turkish TV2 program from Istanbul (distance more than 600 km) are received with good quality.

It was already noted above that installing an antenna amplifier near the TV between the feeder and the antenna input of the television receiver increases the gain of the receiving path, i.e. improves the sensitivity limited by the gain.

It has been shown that when using modern televisions, this method does not lead to improved images in long-distance reception conditions, since it requires an improvement in sensitivity, which is limited not by gain, but by noise. The antenna amplifier, having approximately the same noise level as a television receiver, does not improve noise-limited sensitivity.

Nevertheless, the use of an antenna amplifier in some cases can improve reception, but for this it should be installed not near the TV, but near the antenna, on the mast between the antenna and the feeder, or in the feeder gap, in the immediate vicinity of the antenna. What's the difference?

The fact is that the signal, passing to the feeder, undergoes attenuation and its level decreases. Attenuation depends on the brand of cable from which the feeder is made. In addition, the greater the attenuation, the greater the length of the feeder and the greater the frequency of the signal, i.e., the number of the channel through which the transmission is received.

When an antenna amplifier is installed near the TV, its input receives a signal that has already been weakened by passing through the feeder, and the ratio of the signal level to the noise level at the input of the antenna amplifier is less than if the antenna amplifier was installed near the antenna when the signal is not attenuated by the feeder. In this case, of course, passing through the feeder, the signal is also weakened, but by the same amount. noise is also reduced. As a result, the signal to noise ratio does not deteriorate.

Television cables of different brands are characterized by the dependence of specific attenuation on frequency. The specific attenuation of a coaxial cable is usually called the attenuation that a signal of a certain frequency experiences when passing through a cable 1 m long.

Specific attenuation is measured in dB/m and is given in reference books in the form of graphical dependences of specific attenuation on frequency or in the form of tables. In Fig. 1 shows such curves for some brands of 75-ohm coaxial cable.

Using them, you can calculate the signal attenuation in a cable for a certain length, on any frequency channel in the meter or decimeter range. To do this, you need to multiply the specific attenuation value obtained from the figure by the length of the feeder, expressed in meters. The result is signal attenuation in decibels.

Rice. 1. Specific attenuation curves of coaxial cables.

The most common type of cable for the feeder is RK 75-4-11, its specific attenuation is 0.05...0.08 dB/m in the range of channels 1-5, 0.12...0.15 dB/m in the range of 6-12 channels and 0.25...0.37 dB/m in the range of 21-69 channels. Hence, with a feeder length of 20 m, the signal attenuation in the feeder on the 12th channel will be only 3 dB, which corresponds to a decrease in signal voltage by 1.41 times, and with a feeder length of 50 m, the attenuation on the 12th channel will be 7.5 dB (decrease I 2.38 times).

In the decimeter range, with a feeder length of 20 m, the attenuation will be equal to 5.0...7.4 dB V, depending on the channel number, which corresponds to a decrease in signal voltage1 by 3.78...2.34 times^, and with a length feeder 50 m - 12.5... 18.5 dB (signal reduction by 4.22...8.41 times).

Thus, with a feeder length of 50 m, given to channel 12, the signal passing through the feeder is reduced by more than half, and the signal-to-noise ratio at the TV input will also be reduced by more than half. If you install an antenna amplifier before the signal enters the feeder, at the same level of input noise of the antenna amplifier as the TV, the gain in signal-to-noise ratio will be more than doubled.

An even more significant gain will be obtained with a longer feeder length or when receiving a signal in the UHF range. The necessary and sufficient gain of the antenna amplifier must be equal to the signal attenuation in the feeder. There is no point in using antenna amplifiers with a gain greater than required.

Several types of antenna amplifiers are available. The most widely used antenna amplifiers for the meter range are the UTDI-1-Sh type (individual range television amplifier for frequencies of ranges 1-1II).

They are designed for all 12 channels" of the meter range and contain a built-in power supply from an AC mains voltage of 220 V. The design of the amplifier allows it to be installed on a mast near the antenna with power supply through the feeder without laying additional wires. The gain of the UTDI-1-Sh amplifier is no less than 12 dB (4 times the voltage), and its noise level is slightly lower than the noise floor of black-and-white and color television receivers.

If the UTDI-1-III amplifiers are band and are designed to amplify a television signal on any of the 12 channels of the meter range, then antenna amplifiers of the UTKTI type (individual channel transistor television amplifier) ​​are single-channel and are designed to amplify the signal of only one, very specific frequency channel of the meter range.

The channel number is indicated after the amplifier type designation. Thus, UTKTI-1 means that the amplifier is designed to amplify the signal on the first frequency channel, and UTKTI-8 is designed to amplify the signal on the eighth channel. Amplifiers of the UKTI type also have a built-in power supply from an alternating current network with a voltage of 220 V.

The gain of UTKTI-1 - UTKTI-5 is not less than 15 dB, and UTKTI-6 - UTKTI-12 is not less than 12 dB. The self-noise level of amplifiers of this type is somewhat lower than that of the UTDI-1-Sh type. The power consumed from the alternating current network UTDI-1-Sh does not exceed 7 W, and UTKTI - 4 W.

Due to the fact that television broadcasting in the UHF range is now becoming increasingly widespread, and the signal attenuation in the feeder in this range is increased, the use of antenna amplifiers designed for this range is becoming relevant. For example, an amplifier type UTAI-21-41 (individual television antenna amplifier, designed for 21-41 channels) with a gain of at least 14 dB in the frequency range 470...638 MHz.

Previously, despite the production of industrial antenna amplifiers, in the magazines "Radio" and in the collections "To Help the Radio Amateur" there were a large number of descriptions and diagrams of antenna amplifiers for self-production. In recent years, such publications have become rare. So, in the collection “To help the radio amateur,” issue 101, p. 24-31 provides a very detailed description of a narrowband antenna amplifier with a tunable amplitude-frequency response by O. Prystaiko and Yu.

Pozdnyakova. The amplifier is tuned to one of the channels of the meter range using a tuning capacitor, the amplifier's bandwidth is 8 MHz, and the gain is 22...24 dB. The amplifier is powered by a constant voltage of 12 V. It makes sense to use such an amplifier only in the case when transmissions are received via one specific channel, since it is not possible to rebuild the amplifier installed on the mast.

Wideband antenna amplifier MV

Much more often there is a need for a broadband antenna amplifier that can amplify the signals of all television programs received by the antenna. In Fig. 2 shown circuit diagram of antenna amplifier, designed to amplify all 12 meter channels, developed by I. Nechaev.

Rice. 2. MV antenna amplifier circuit.

At a voltage of 12 V, the gain is 25 dB with a current consumption of 18 mA. The amplifier is assembled using low-noise transistors with a noise figure of about 3 dB. Back-to-back diodes connected at the input protect the amplifier transistors from damage by lightning discharges. Both cascades are assembled according to a common emitter circuit.

Capacitor C6 provides correction of the frequency response of the amplifier in the higher frequencies.

The output of the amplifier is connected to the feeder going to the TV. The central core of this part of the feeder supplies the amplifier with supply voltage through inductor N. Through the same inductor, a voltage of +12 V is supplied to the central conductor of the antenna socket of the TV. The signal from the antenna socket on the TV to the input of the channel selector must be supplied through an isolation capacitor with a capacity of 3000 pF.

The chokes are wound on ferrite cylindrical cores with a diameter of 3 mm and a length of 10 mm using PEL or PEV wire with a diameter of 0.2 mm turn to turn. Each inductor contains 20 turns. Before winding, the core must be wrapped in two layers of lavsan film, and after winding, the turns are secured with polystyrene varnish or enamel.

A more detailed description of the amplifier, a drawing of the printed circuit board and the placement of parts on it are given in the magazine "Radio", 1992, No. 6, p. 38-39.

Another antenna amplifier, designed for the UHF range 470...790 MHz (21...60 channels), was proposed by A. Komok. Its circuit diagram is shown in. rice. 3. The passband gain of this amplifier is 30dB when powered at 12V, and the current consumption does not exceed 12mA.

Rice. 3. UHF antenna amplifier circuit.

The high-pass filter coil L1 is wound with PEV-2 wire with a diameter of 0.8 mm and contains 2.5 turns.

Winding is carried out on a mandrel with a diameter of 4 mm turn to turn, after which the coil is removed from the mandrel. Power, as for the Nechaev amplifier, is supplied through the feeder through the chokes of the design described above. The author used unpackaged transistors in the amplifier, which require careful sealing.

We can also recommend the use of KT399A packaged transistors, which are more affordable and resistant to changes in climatic conditions. A detailed description of this amplifier is published in the magazine Radio Amateur 11, 1993, No. 5, p. 2.

As noted, the main purpose of the antenna amplifier is to compensate for signal attenuation in the feeder. When using an antenna amplifier, noise-limited sensitivity, i.e., the ability to receive a weak signal, is determined by the signal-to-noise ratio not at the input of the television receiver, but at the input of the antenna amplifier. Therefore, when installing an antenna amplifier near an antenna, to obtain a certain sensitivity value limited by noise, a lower input signal level will be required than when installing it near a TV. Thus, it is possible to receive a weaker signal with better quality.

Application of antenna amplifier allows the deliberate use of feeders of such great length that, in the absence of an amplifier, would weaken the signal level to an unacceptable level. The need to use a long feeder sometimes arises in closed areas, when the television receiver is located in a hollow and the receiving antenna installed near the house is obscured by hills on the way to the transmitter.

At the same time, television antennas installed at a distance of 100...200 m from this building provide quite reliable reception with good image quality due to the fact that they are not covered by a local obstacle. In such conditions, normal reception can be achieved in one of two ways: either by increasing the height of the antenna mast, which is usually a very difficult task, or by installing the antenna in an open area, at a distance of 100...200 m from the house. Then to connect the antenna to the television receiver you will need to use a long feeder.

It is easy to calculate that with a feeder length of 200 m, a cable of the RK 75-4-11 brand at the frequency of the 12th channel creates an attenuation of 30 dB, which corresponds to a decrease in signal voltage by 31.6 times, which, as a rule, is below the sensitivity threshold of a television receiver . Installing an antenna amplifier with at least the same gain at the antenna output will compensate for signal attenuation in a long feeder and ensure normal operation of the TV.

If the gain of one amplifier is not enough, you can connect two amplifiers in series one after the other. In this case, the resulting gain will be equal to the sum of the gains of the amplifiers, if they are expressed in decibels.

If the feeder length is very long and the signal needs to be amplified by more than 30 dB, when it is necessary to use two or more antenna amplifiers, in order to avoid overload or self-excitation, all amplifiers should not be installed in one place. Under these conditions, the first amplifier is installed at the antenna output, i.e., at the input of the feeder, and the subsequent ones are installed in the feeder gap at approximately equal distances from one another. These distances are chosen so that the signal attenuation in the feeder section between the two amplifiers is approximately equal to the gain of the amplifier.

From the dependences of specific attenuation on frequency for coaxial cables of different brands (Fig. 1), certain conclusions can be drawn. Cables of brands RK 75-2-13 and RK 75-2-21 have a fairly high specific attenuation even in the meter wavelength range; they should not be used in the decimeter wavelength range. Cables of brands RK 75-7-15, RK 75-9-13, RK 75-13-11 and RK 75-17-17 have lower specific attenuation compared to RK 75-4-11, especially in the decimeter range.

If, with a feeder length of 50 m at a frequency of 620 MHz (channel 39), the RK 75-4-11 cable introduces an attenuation of 16 dB (attenuation of the signal voltage by 6.3 times), then under the same conditions the RK 75-9 cable -13 introduces an attenuation of 9.5 dB (attenuation by 3 times), and RK 75-13-1.1 - 7.25 dB (attenuation by 2.3 times). Thus, a successful choice of cable brand for a feeder in the UHF range can increase the signal level at the TV input several times, even without using an antenna amplifier.

We can offer fairly simple advice on cable selection: the larger the cable diameter, the less attenuation it introduces. A coaxial cable with a characteristic impedance of 75 Ohms is always used as a television feeder.

Nikitin V.A., Sokolov B.B., Shcherbakov V.B. - 100 and one antenna designs.

Despite the rapid development of satellite and cable television, the reception of terrestrial television broadcasts still remains relevant, for example, for places of seasonal residence. It is not at all necessary to buy a finished product for this purpose; a home UHF antenna can be assembled with your own hands. Before moving on to considering the designs, we will briefly explain why this particular range of the television signal was chosen.

Why DMV?

There are two good reasons to choose designs of this type:

1. The thing is that most channels are broadcast in this range, since the design of repeaters is simplified, and this makes it possible to install a larger number of unattended low-power transmitters and thereby expand the coverage area.
2. This range is selected for digital broadcasting.

Indoor TV antenna “Rhombus”

This simple, but at the same time, reliable design was one of the most common in the heyday of on-air television broadcasting.

Rice. 1. The simplest homemade Z-antenna, known under the names: “Rhombus”, “Square” and “People’s Zigzag”

As can be seen from the sketch (B Fig. 1), the device is a simplified version of the classic zigzag (Z-design). To increase sensitivity, it is recommended to equip it with capacitive inserts (“1” and “2”), as well as a reflector (“A” in Fig. 1). If the signal level is quite acceptable, this is not necessary.

The material you can use is aluminum, copper, and brass tubes or strips 10-15 mm wide. If you plan to install the structure outdoors, it is better to abandon aluminum, since it is susceptible to corrosion. Capacitive inserts are made of foil, tin or metal mesh. After installation, they are soldered along the circuit.

The cable is laid as shown in the figure, namely: it did not have sharp bends and did not leave the side insert.

UHF antenna with amplifier

In places where a powerful relay tower is not located in relative proximity, you can raise the signal level to an acceptable value using an amplifier. Below is a schematic diagram of a device that can be used with almost any antenna.

Rice. 2. Antenna amplifier circuit for the UHF range

List of elements:

• Resistors: R1 – 150 kOhm; R2 – 1 kOhm; R3 – 680 Ohm; R4 – 75 kOhm.
• Capacitors: C1 – 3.3 pF; C2 – 15 pF; C3 – 6800 pF; C4, C5, C6 – 100 pF.
• Transistors: VT1, VT2 – GT311D (can be replaced with: KT3101, KT3115 and KT3132).

Inductance: L1 – is a frameless coil with a diameter of 4 mm, wound with copper wire Ø 0.8 mm (2.5 turns must be made); L2 and L3 are high-frequency chokes 25 µH and 100 µH, respectively.

If the circuit is assembled correctly, we will get an amplifier with the following characteristics:

• bandwidth from 470 to 790 MHz;
• gain and noise factors – 30 and 3 dB, respectively;
• the value of the output and input resistance of the device corresponds to the RG6 cable – 75 Ohm;
• the device consumes about 12-14 mA.

Let's pay attention to the method of power supply; it is carried out directly through the cable.

This amplifier can work with the simplest designs made from improvised means.

Indoor antenna made from beer cans

Despite the unusual design, it is quite functional, since it is a classic dipole, especially since the dimensions of a standard can are perfectly suitable for the arms of a decimeter range vibrator. If the device is installed in a room, then in this case it is not even necessary to coordinate with the cable, provided that it is not longer than two meters.

Designations:

• A - two cans with a volume of 500 mg (if you take tin and not aluminum, you can solder the cable instead of using self-tapping screws).
• B – places where the cable shielding is attached.
• C – central vein.
• D – place of attachment of the central core
• E – cable coming from the TV.

The arms of this exotic dipole must be mounted on a holder made of any insulating material. As such, you can use improvised things, for example, a plastic clothes hanger, a mop bar or a piece of wooden beam of appropriate size. The distance between the shoulders is from 1 to 8 cm (selected empirically).

The main advantages of the design are fast production (10 - 20 minutes) and quite acceptable picture quality, provided there is sufficient signal power.

Making an antenna from copper wire

There is a design that is much simpler than the previous version, which only requires a piece of copper wire. We are talking about a narrow band loop antenna. This solution has undoubted advantages, since in addition to its main purpose, the device plays the role of a selective filter that reduces interference, which allows you to confidently receive a signal.

Fig.4. A simple UHF loop antenna for receiving digital TV

For this design, you need to calculate the length of the loop; to do this, you need to find out the frequency of the “digit” for your region. For example, in St. Petersburg it is broadcast on 586 and 666 MHz. The calculation formula will be as follows: L R = 300/f, where L R is the length of the loop (the result is presented in meters), and f is the average frequency range, for St. Petersburg this value will be 626 (the sum of 586 and 666 divided by 2). Now we calculate L R, 300/626 = 0.48, which means the length of the loop should be 48 centimeters.

If you take a thick RG-6 cable with braided foil, it can be used instead of copper wire to make a loop.

Now let's tell you how the structure is assembled:

• A piece of copper wire (or RG6 cable) with a length equal to L R is measured and cut.
• A loop of suitable diameter is folded, after which a cable leading to the receiver is soldered to its ends. If RG6 is used instead of copper wire, then the insulation from its ends is first removed, approximately 1-1.5 cm (the central core does not need to be cleaned, it is not involved in the process).
• The loop is installed on the stand.
• The F connector (plug) is screwed onto the cable to the receiver.

Note that despite the simplicity of the design, it is most effective for receiving “digits”, provided that the calculations are carried out correctly.

Do-it-yourself MV and UHF indoor antenna

If, in addition to UHF, there is a desire to receive MF, you can assemble a simple multiwave oven, its drawing with dimensions is presented below.

To amplify the signal, this design uses a ready-made SWA 9 unit; if you have problems purchasing it, you can use a home-made device, the diagram of which was shown above (see Fig. 2).

It is important to maintain the angle between the petals; going beyond the specified range significantly affects the quality of the “picture”.

Despite the fact that such a device is much simpler than a log-periodic design with a wave channel, it nevertheless shows good results if the signal is of sufficient power.

DIY figure eight antenna for digital TV

Let's consider another common design option for receiving “digits”. It is based on the classic scheme for the UHF range, which, because of its shape, is called “Figure Eight” or “Zigzag”.

Rice. 6. Sketch and implementation of the digital eight

Design dimensions:

• outer sides of the diamond (A) – 140 mm;
• internal sides (B) – 130 mm;
• distance to the reflector (C) – from 110 to 130 mm;
• width (D) – 300 mm;
• the pitch between the rods (E) is from 8 to 25 mm.

The cable connection location is at points 1 and 2. The material requirements are the same as for the “Rhombus” design, which was described at the beginning of the article.

Homemade antenna for DBT T2

Actually, all of the examples listed above are capable of receiving DBT T2, but for variety we will present a sketch of another design, popularly called “Butterfly”.

The material can be used as plates made of copper, brass, aluminum or duralumin. If the structure is planned to be installed outdoors, then the last two options are not suitable.

Bottom line: which option to choose?

Oddly enough, the simplest option is the most effective, so the “loop” is best suited for receiving a “digit” (Fig. 4). But, if you need to receive other channels in the UHF range, then it is better to stop at “Zigzag” (Fig. 6).

The antenna for the TV should be directed towards the nearest active repeater, in order to select the desired position, you should rotate the structure until the signal strength is satisfactory.

If, despite the presence of an amplifier and reflector, the quality of the “picture” leaves much to be desired, you can try installing the structure on a mast.

In this case, it is necessary to install lightning protection, but this is a topic for another article.

Although television is constantly evolving, expanding the network and increasing the capabilities of television equipment are not a guarantee of high picture quality. The specificity of the TV signal limits the distance over which it can be transmitted. In mountainous areas and in areas far from the tower, carrier waves arrive greatly weakened, which makes it impossible to receive individual channels.

In addition, incorrect design and shape of the antenna, errors in its installation, distance from the receiving and transmitting radio equipment - all this also negatively affects the picture level.

The solution to this problem is to create an antenna amplifier for digital television with your own hands.

Features and circuit of the antenna amplifier

An amplifier is a device designed to amplify a poor, unstable TV antenna signal. The advantages of this device are as follows:

• amplification of a television signal in a fairly wide frequency band;
• the ability to receive even a very weak TV signal;
• quiet operation.

The disadvantages include:

• the risk that the device will self-excite;
• High power signals in the meter wave range may overload the device;
• susceptibility to the effects of lightning currents;
• passive output losses.

The DIY antenna amplifier diagrams indicate how the device should be connected to the TV. The TV cable goes to a device that amplifies the signal, and then the signal goes to the TV. This scheme is universal.

Antenna amplifier for UHF

Modern digital television is broadcasting on decimeter waves (UHF). Frequency range – from 470 to 1270 MHz. The simplest solution for long- and ultra-long-range TV signal reception in the UHF range is to use a structurally simple antenna with an amplifier located close to it, which one can easily make with one’s own hands.

A DIY UHF antenna amplifier must have a significant gain, create a minimum of noise during operation and be resistant to temperature changes

A simple design, availability of the raw materials necessary for its creation and the absence of a tendency to self-excitation are other important requirements for such a device.

Antenna amplifier for FM receiver

To make an fm antenna amplifier at home, you will need:

• large round aluminum plate;
• a piece of copper wire;
• tractor rubber belt;
• TV cable;
• metal bracket (preferably aluminum);
• adapter;
• self-tapping screws – 4 pcs., nuts – 2 pcs., bolts – 2 pcs., washers – 2 pcs.

You also need to prepare a hammer, screwdriver, wrench, drill, pliers and soldering iron. You also need to take care of the presence of electrical tape.

Here are brief instructions on how to properly make an antenna amplifier for an FM receiver:

• Make a hole of the required size in the aluminum plate
• Cut 1 large piece from the tractor rubber and make three similar holes.
• Drill the same holes in the bracket, do not forget about the holes for mounting the antenna.
• Bend the wire, make holes in it, and connect the ends using a self-tapping screw.
• Connect the adapter to the cable and insulate the connection.
• Assemble all the elements of the device into one whole, using bolts with washers and nuts, self-tapping screws. Insulate the fastening of the cable contacts to the wire with electrical tape.

Rules for choosing a signal amplifier

When choosing an antenna amplifier, you need to carefully study the following points:

• distance from the repeater (optimal value 10 – 150 km);
• frequency range;
• the magnitude of the TV signal at the output of the device (preferably 100 dB per µV);
• gain (should not be less than 40 dB);
• the type of equipment that needs signal amplification;
• noise level produced (should not be more than 3 dB);
• current required for operation (usually from 30 to 60 A);
• location (near the device or at the receiver).

An antenna amplifier is a radio engineering device that allows you to improve the quality of TV signal reception. If you have problems with the television picture, then do not be lazy to make this device.

As can be seen in the photo of the antenna amplifier, a device of even the simplest design will significantly increase the level of the received signal.

DIY antenna amplifier photo