Menu English Ukrainian russian Home

Free technical library for hobbyists and professionals Free technical library


ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Tunable low noise antenna amplifier. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Antenna amplifiers

Comments on the article Comments on the article

By using an antenna amplifier, you can improve the quality of reception of television and radio broadcasting programs at the border of the reliable reception zone. The version of such an amplifier proposed in the article has a significant advantage - not only the supply voltage is supplied through the signal cable, but also the operating frequency of the device is tuned.

To improve the quality of the television image and sound or the sound of broadcasting stations, directional antennas have to be used, as well as antenna amplifiers. When receiving a weak signal from a remote television center and there are strong signals from local television or radio broadcasting stations, cordless telephones, etc., broadband antenna amplifiers often do not have a positive effect due to signal overload from nearby transmitters.

In this case, selective antenna amplifiers help out.

To receive signals from several channels, the amplifier must be tunable. However, when such amplifiers are placed near the antenna, a separate wire is required for tuning, which is not very convenient from a structural point of view. In the proposed antenna amplifier, restructuring occurs when the supply voltage supplied through the drop cable changes.

The circuit diagram of the amplifier is shown in fig. 1. It provides frequency dependent gain from 18(50MHz) to 14(230MHz) dB. It uses a low-noise gallium arsenide field-effect transistor, which makes it possible to obtain high sensitivity. The input circuit, formed by the inductance of the coil L1 and the capacitances of the varicap, diodes and transistor, provides frequency selection of the signal and matching the high input impedance of the transistor with the low output impedance of the antenna. The circuit is rebuilt by changing the capacitance of the varicap when adjusting the voltage applied to it.

Tunable low noise antenna amplifier

The supply voltage of the transistor is stabilized by a microcircuit voltage regulator DA1. The DC transistor mode is set by resistors R2, R3. To match with the drop cable, an L2 coil with a tap is used. Diodes VD1, VD2, VD4, VD5 protect the transistor from breakdown by powerful signals and pickups. The supply voltage to the amplifier is supplied via the drop cable through the L3 inductor.

For tuning, an adjustable voltage from 7 to 15 V is supplied to the amplifier from a stabilized power supply located next to the TV or radio. This voltage is applied to the stabilizer DA1, and through the zener diode VD6 - to the varicap VD3. At a supply voltage of 7 V, a current begins to flow through the zener diode VD3 and a voltage of about 0,2 V is applied to the varicap. In this case, its capacitance is maximum and the circuit is tuned to the lower frequency of the tuning interval. As the supply voltage on the varicap increases, it also increases, the capacitance of the varicap decreases, and the tuning frequency of the input circuit increases.

The frequency overlap factor of the input circuit is slightly less than two. This means that the amplifier can be used to receive television signals in the MB1 subband (48 ... 100 MHz) or in the MB2 subband (174 ... 230 MHz), as well as to receive only radio station programs in the VHF bands (65 ... 108 MHz). To do this, change the parameters of the coil L1.

The power supply of the antenna amplifier is provided by the block, the diagram of which is shown in fig. 2. It is assembled on an integral adjustable stabilizer. The output voltage of the block is changed by resistor R3. Through the L1 choke, it enters the XS1 socket, to which the drop cable from the antenna amplifier is connected. The received signals from the socket XS1 pass through the capacitor C4 along the cable with the XP2 plug. It is connected to the TV input.

Tunable low noise antenna amplifier

In the amplifier, in addition to those indicated in the diagram, transistors AP325A-2, AP331A-2 or similar, varicaps KV109A, KV109V, KV109G, KV122A, KV122B, KV122V, zener diode KS168A, diodes KD512A, KD514A are applicable. It is desirable to use small-sized resistors: P1-4, P1-12 or MLT. It is better to use open-frame capacitors K10-17V or small-sized capacitors with leads of a minimum length.

Coils L2, L3 are wound with PEV-2 0,12 wire on K5x2x1,5 ferrite rings with a permeability of 600 ... 2000. Coil L2 contains 10 turns in two twisted wires (after winding, the beginning of one wire is connected to the end of the other and an average output is obtained), coil L3 - 15-20 turns of a single wire. Coil L1 is wound with wire PEV-2 0,9 on a mandrel with a diameter of 5 mm. If the coil has 11,5 turns (tap from the third turn), the tuning interval is 48 ... 92 MHz, if 6,5 turns (tap from the second turn) - the interval is 65 ... 110 MHz, and if 3,5 turns (tap from 0,3 ... 0,5 of the first turn) - 150 ... 230 MHz. For a slight shift in the tuning interval towards higher frequencies, the coil turns are slightly moved apart.

In the power supply, you can use polar capacitors of the K50 series, non-polar K10-17, KD or KT, a variable resistor - SPO, SP4, constant MLT, S2-33. Inductor L1 is similar to inductor L3 in the amplifier. The transformer must provide an alternating voltage on the secondary winding of about 15 V.

Setting up the amplifier comes down to setting the required tuning interval by selecting the number of turns of the L1 coil and a bandwidth of at least 7 MHz by changing the tap location. In the power supply, by selecting resistors R2 and R3, the required interval for changing the output voltage is set. When the amplifier is self-excited at high frequencies, a ferrite ring (“bead”) must be put on the drain terminal of the transistor or an adhesive composition (based on epoxy glue) with a filler of powdered carbonyl iron should be applied.

All parts of the amplifier are placed on a printed circuit board made of double-sided foil fiberglass. The arrangement of printed conductors is shown in fig. 3. The second side of the board is left metallized, except for the input and output pad cutouts indicated by the dashed line, and is connected by foil to the common wire of the first side along the entire circuit. After installation and adjustment, the field-effect transistor is poured with a drop of epoxy glue, the board is closed from the side of the parts with a metal cover-screen, and the device is covered on all sides with a protective layer of waterproof paint or varnish.

Tunable low noise antenna amplifier

The parts of the power supply are installed on a printed circuit board made of one-sided foil-coated fiberglass, the printed conductors of which are shown in fig. 4.

Tunable low noise antenna amplifier

The amplifier can be made switchable by adding two relays to it, turning them on in accordance with the diagram in fig. 5, then when the supply voltage is turned off, the antenna will be connected directly to the drop cable, bypassing the amplifier. To do this, you can use the RES-34, REC-43 relays with a response voltage of about 6 V. The dimensions of the board will have to be increased, and the wiring of the conductors will have to be slightly changed.

Author: I.Nechaev

See other articles Section Antenna amplifiers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive

Samsung is preparing to release flexible displays 25.11.2012

In the first half of 2013, Samsung intends to start mass production of the so-called flexible displays. With a plastic backing, they are stronger, lighter, and cheaper than modern displays that use glass as a base. Samsung Display is preparing to mass-produce displays with a plastic base instead of glass, which will make devices stronger, lighter and even more flexible, according to the Wall Street Journal, citing a source familiar with the situation.

The displays will be based on OLED technology, meaning they will use LEDs. This technology is used in displays for Samsung's flagship smartphones and is gradually beginning to be introduced into TVs. OLED technology allows the construction of thin panels that, using plastic as a base, can be bent without destroying the electronics. In addition, such panels are lighter in comparison with modern panels, which are based on glass.

The development of flexible OLED panels has been going on for the past few years. In addition to Samsung, Japanese companies Sony, Sharp and Korean LG Display participate in it. For example, Sony Corporation has been in this field since 2002. Two years ago, Sony showed off a 4,1-inch flexible LED display that it developed. However, there are no commercial devices based on such displays yet, due to technological limitations in mass production.

"Samsung's main goal is to use plastic instead of the traditional glass substrate to create shatterproof displays. This technology can also help reduce product costs and differentiate products in the market," said Lee Seung-chul, an analyst at Shinyoung Securities.

The WSJ writes that Samsung Display is currently in the final stages of developing flexible displays. It is planned to release them on the market in the first half of 2013, and the company expects to become their first manufacturer. Samsung Display Vice President Lee Chang-hoon said the company is shipping test samples of flexible displays to several of its partners today. However, he could not name the exact date for the release of the first products based on them, since it has not yet been determined. Previously circulated information that the Samsung Galaxy Note II will be equipped with a flexible display.

Other interesting news:

▪ Vacuum cleaner for cameras with interchangeable lenses

▪ Probiotics protect against depression

▪ Ford cars will learn to track free parking lots

▪ Cells responsible for alcohol cravings discovered

▪ Honor Clear Headphones with Heart Rate Recording

News feed of science and technology, new electronics

 

Interesting materials of the Free Technical Library:

▪ site section Tone and volume controls. Article selection

▪ article In the main - unity, in the secondary - freedom, in everything - love. Popular expression

▪ article What is nutmeg? Detailed answer

▪ article Caring for horses and transport work. Standard instruction on labor protection

▪ article Another antenna with a capacitive load. Encyclopedia of radio electronics and electrical engineering

▪ article Voltage regulator on a CMOS chip. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

Name:


Email (optional):


A comment:





All languages ​​of this page

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua

www.diagram.com.ua
2000-2024