ALC in the power output stage. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
Comments on the article
It is a pity that many radio amateurs, including myself, did not pay due attention to ALC systems in the output stages of the transmitter at one time. After experimenting, especially with tubes of high steepness, I came to the conclusion that ALC is an integral part of the power amplifier. It is known that the appearance of the grid current of the control grid creates a number of spectral problems and, above all, in the immediate vicinity of the frequency of its transmitter. The expansion of the emission band, the so-called "splatters", cause angry criticism from radio amateurs who find themselves in their coverage area.
Of course, by including the measuring device in the control grid circuit, it is possible to control the magnitude of the grid current, but it is difficult to track its peak values due to the inertia of the magnetoelectric system of the device.
The introduction of an ALC system into the power amplifier circuit makes it possible, firstly, to negate the above disadvantage, and secondly, to increase the average output power by limiting the peak RF current.
(click to enlarge)
Figure 1 shows the ALC circuit. Its work is reduced to receiving the voltage supplied to the external ALC input of the RA3AO transceiver. A low-frequency transformer Tr is installed in the control grid circuit of the output stage lamp. For this purpose, almost any output transformer from transistor radios is suitable.
The signal is taken from the high-resistance winding I and fed through a carefully shielded wire to a broadband amplifier assembled on a low-noise integrated amplifier K548UN1B. The amplifier has a bandwidth of 2 Hz to 100 kHz. Noise figure - 2 dB.
The gain depends on the ratio of resistors R1 and R2. It is calculated by the formula Kus = Rl / R2 and is selected individually for each transceiver and power amplifier. The amplified signal is detected by a half-wave rectifier.
The charging and discharging time of the capacitor C1 determines the time constant of the ALC as a whole. A small capacitance of the capacitor leads to the appearance of "pops", and a large capacitance will not allow you to work out fast changes in high-frequency voltage. To reduce the discharge time of the capacitor C1, you may have to install and select an additional resistor R5 * in the base circuit of the regulating transistor VT1.
With a control grid current of about 10 mA, the voltage across capacitor C1 can reach 11 V. This voltage is more than enough to control the transceiver.
The amplifier on the DA1 chip is high-resistance, and therefore it is very sensitive to various noises and pickups, so it must be carefully shielded, powered from a stabilized voltage source, and the shielded wire from the primary winding of the transformer should be soldered at the amplifier itself. The amplifying stage can be placed in the transceiver itself (this is how I did it) and connected to the output stage with a shielded cable.
From the emitter of the transistor VT1, the ALC voltage is supplied directly to the transceiver without any additions. Sometimes some transformers do not provide the proper transformation ratio, so the transformer should be selected for each specific case. The K548UN1B chip can be replaced with any low-noise operational amplifier. Transistor VT1 can be replaced with a less powerful one, but in this case it may be necessary to shunt capacitor C1 with a resistor, the value of which should be selected.
Working with ALC, the power of the transceiver can be smoothly changed from a certain minimum. Gradually increasing the "buildup", it should be noted the moment when the output device of the transceiver no longer notes an increase in the output signal level. Do not set it to full power, as there is an increased level of noise in the output signal.
(*) The title of this article has been left unchanged, although, in my opinion, it is not possible to call what has been stated by the ALC system of a powerful RA. I think it's still about something else. (Note RW3AY).
Author: S.Volkovinsky, RA9FOR, Perm; Publication: N. Bolshakov, rf.atnn.ru
See other articles Section Civil radio communications.
Read and write useful comments on this article.
<< Back
Latest news of science and technology, new electronics:
The world's tallest astronomical observatory opened
04.05.2024
Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>
Controlling objects using air currents
04.05.2024
The development of robotics continues to open up new prospects for us in the field of automation and control of various objects. Recently, Finnish scientists presented an innovative approach to controlling humanoid robots using air currents. This method promises to revolutionize the way objects are manipulated and open new horizons in the field of robotics. The idea of controlling objects using air currents is not new, but until recently, implementing such concepts remained a challenge. Finnish researchers have developed an innovative method that allows robots to manipulate objects using special air jets as "air fingers". The air flow control algorithm, developed by a team of specialists, is based on a thorough study of the movement of objects in the air flow. The air jet control system, carried out using special motors, allows you to direct objects without resorting to physical ... >>
Purebred dogs get sick no more often than purebred dogs
03.05.2024
Caring for the health of our pets is an important aspect of the life of every dog owner. However, there is a common assumption that purebred dogs are more susceptible to diseases compared to mixed dogs. New research led by researchers at the Texas School of Veterinary Medicine and Biomedical Sciences brings new perspective to this question. A study conducted by the Dog Aging Project (DAP) of more than 27 companion dogs found that purebred and mixed dogs were generally equally likely to experience various diseases. Although some breeds may be more susceptible to certain diseases, the overall diagnosis rate is virtually the same between both groups. The Dog Aging Project's chief veterinarian, Dr. Keith Creevy, notes that there are several well-known diseases that are more common in certain breeds of dogs, which supports the notion that purebred dogs are more susceptible to disease. ... >>
| Random news from the Archive Astronauts will be sent to the captured asteroids
11.04.2013
Asteroids are one of the smallest space objects, but they have long attracted the attention of the scientific community. Amateur astronomers are trying to find them; professionals study the composition, calculate the trajectory, try to understand their "pedigree". Enthusiast billionaires are even planning attempts to generate super-profits by mining asteroids. But first of all, everyone is interested in the threat of asteroid collisions with the Earth and methods of preventing global and local disasters.
Many hypotheses have been put forward, in what way it is better to change the trajectory of a celestial body or even destroy it. But they all have drawbacks and require careful testing. Surprisingly, however, the possibility of capturing asteroids, transporting them to Earth is being considered. Here, astronauts will be sent to them for a full-scale study of these celestial bodies. Sounds fantastic, but this is exactly the kind of strategy being considered by the National Aerospace Agency NASA.
It should be noted that such plans are in perfect agreement with the long-term plans for the development of the space industry, adopted by the administration of President Obama. According to them, by 2025 the first flights of astronauts to asteroids located at a relatively small distance from the Earth should take place. Then the time will come for a manned flight to Mars.
The study of asteroids in the course of manned missions is not limited to studying the possibility of removing space threats from the Earth. As already mentioned, these space objects are rich in minerals, and their extraction and transportation to Earth is another task to be solved.
So, NASA is currently working on planning a mission to capture asteroids with a robot, deliver it to Earth, and then study it by astronauts. To accomplish this ambitious task, no doubt, it will require the cooperation of a number of large companies, the joint work of research and engineering teams from various countries, the development of new technologies and unique devices. It is possible that the colossal efforts will eventually be justified.
|
Other interesting news:
▪ poisoned planet
▪ Ancient mines and modern ecology
▪ Audiophile player Walkman NW-A105
▪ E Ink Color Paper
▪ New implant allows you to hear the light
News feed of science and technology, new electronics
Interesting materials of the Free Technical Library:
▪ section of the site Radioelectronics and electrical engineering. Article selection
▪ article Administrative delight. Popular expression
▪ article Which two countries are ahead of Hollywood in terms of the number of films produced per year? Detailed answer
▪ article Driver in the transport of dangerous goods. Standard instruction on labor protection
▪ article Musical play of light. Encyclopedia of radio electronics and electrical engineering
▪ article Additional protection of the stabilizer from overheating. Encyclopedia of radio electronics and electrical engineering
Leave your comment on this article:
All languages of this page
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua
2000-2024
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese