Methods for setting up and adjusting radio and television equipment. Labor protection requirements during work. Adjustment of radio-electronic equipment and devices

Remote control of moving models is based on interaction between a person and a model. The pilot sees the position of the model in space and its speed. Using equipment remote control he gives commands to actuators models that turn rudders or control engines, thereby the pilot changes the position and direction of movement of the model in accordance with his desire. The transmission of commands from the pilot to the model occurs mostly via radio. An exception can be found only for indoor models, where, along with a radio, they use infrared radiation, and very rarely ultrasound is used to control underwater vehicles.

The radio control equipment consists of a transmitter, which is located by the pilot, and a receiver and actuators located on the model. This article will help you gain an understanding of how a transmitter works and which transmitter you need.

Design types of transmitters

Based on the design of the controls, which are actually acted upon by the pilot’s fingers, transmitters are divided into joystick and pistol type. The first ones usually have two two-axis joysticks. Such transmitters are used to control flying models. In joystick transmitters, the handle has built-in springs that return it to the neutral position when released. As a rule, one of the directions of some kind of joystick is used to control the traction motor - it does not have a return spring. In this case, the handle is pressed with a ratchet (for airplanes) or a smooth braking plate (for helicopters). Using such transmitters, you can also successfully control floating and driving models, but special pistol-type transmitters have been invented for them. Here the steering wheel controls the direction of movement of the model, and the trigger controls its engine and brakes.

IN last years transmitters with one two-axis joystick appeared. They belong to the category of cheap devices and can be used to control both simplified flying and ground equipment. They can be used productively only at the most basic level. Transmitters with two single-axis joysticks have a similar purpose:

To end with constructive varieties Let's also add a division of joystick transmitters into monoblock and modular. If the first ones are fully equipped with all components and are immediately ready for use, then the modular ones represent a basis into which the pilot, at his discretion, adds the additional controls he needs:

There are two ways to hold the transmitter. Remote control transmitters are hung around the pilot's neck using a special belt or stand. The pilot's hands rest on the transmitter body, and each joystick is controlled by two fingers - the index and thumb. This is the so-called European school. The pilot holds the handheld transmitter in his hands, and each joystick is controlled by one thumb. This manner is attributed to the American school.

The handheld transmitter can also be held in your hands and controlled in a European way. You can also use it in a remote control version if you buy a special table-stand for it. You can make a table no worse than a branded one yourself. Such tables are also required for some remote control transmitters. Which manner is more common among us depends on the age of the pilot. Young people, according to our observations, are more inclined to American customs, and the older generation is more inclined to the conservatism of Europe.

Number of channels and control knob layout

Controlling moving models requires influencing several functions simultaneously. Therefore, radio control transmitters are made multi-channel. Let's consider the number and purpose of channels.

For cars and ship models, two channels are needed: control of the direction of movement and engine speed. Sophisticated pistol transmitters also have a third channel, which can be used to control the mixture formation of the internal combustion engine (radio needle).

To control the simplest flying models, two channels can also be used: elevators and ailerons for gliders and airplanes, or elevators and rudder. For hang gliders, roll control and motor power are used. This scheme is also used on some simple gliders - rudder and engine switching on. Such two-channel transmitters can be used for fleet models and entry-level electric aircraft. However, to fully control an airplane you need at least four, and a helicopter - five channels. For aircraft, two two-axis joysticks provide control functions for the elevator, direction, ailerons and engine throttle. The specific layout of functions for joysticks is of two types: Mode 1 - elevator on the left vertically and rudder horizontally, gas on the right vertically and roll horizontally; Mode 2 - gas on the left vertically and rudder horizontally, elevator on the right vertically and roll horizontally. There are also Mode 3 and 4, but they are not very common.

Mode 1 is also called the two-handed version, and Mode 2 is called the one-handed version. These names follow from the fact that in the latter version you can control the plane for quite a long time with one hand, holding a can of beer in the other. Modellers' debate about the advantages of one scheme or another has not subsided for many years. For the authors, these disputes are reminiscent of the debate about the advantages of blondes over brunettes. In any case, most transmitters can easily be switched from one layout to another.

To effectively control a helicopter, you already need five channels (not counting the channel for controlling the sensitivity of the gyroscope). Here there is a combination of two functions per direction of the joystick (we will look at how this happens later). The handle layouts are in many ways similar to airplane ones. Among the features is the throttle stick, which some pilots invert (minimum throttle is at the top, maximum throttle is at the bottom), as they find it more convenient.

Above, we considered the minimum required number of channels to control the movement of models. But there can be a lot of functions for managing models. Especially on copy models. On airplanes, this can be control of landing gear retraction, flaps and other wing mechanization, side lights, and landing gear wheel brakes. More more features in replica ship models that imitate various mechanisms real ships. Gliders use control of flaperons and air brakes (interceptors), retractable landing gear and other functions. Helicopters also use control over the sensitivity of the gyroscope, retractable landing gear, and others. additional functions. To control all these functions, transmitters are available with a number of channels of 6, 7, 8 and up to 12. In addition, modular transmitters have the ability to increase the number of channels.

It should be noted here that control channels are of two types - proportional and discrete. The easiest way to explain this is in a car: gas is a proportional channel, and headlights are discrete. Currently, discrete channels are used only to control auxiliary functions: turning on the headlights, releasing the landing gear. All main control functions are carried out through proportional channels. In this case, the amount of steering wheel deflection on the model is proportional to the amount of joystick deflection on the transmitter. So, in modular transmitters it is possible to expand the number of both proportional and discrete channels. We will look at how this is done technically later.

There is one fundamental ergonomic problem associated with multichannel. A person has only two hands, which can control only four functions at a time. On real airplanes, pilots' feet (pedals) are also used. Modelers haven't come to this point yet. Therefore, the remaining channels are controlled from separate toggle switches for discrete channels or knobs for proportional ones, or these secondary functions obtained by calculation from the basic ones. In addition, the model control signals may also not be directly controlled from the joysticks, but undergo pre-processing.

Control signal processing and mixing

After reading the previous chapters, we hope you were able to understand two main points:

• The transmitter can be held in different ways, but the main thing is not to drop it
• There are many channels in transmitters, but you always have to control them with only two hands, which is sometimes not very easy

Now that we have a preliminary understanding, let's look at a few more practical points that transmitters implement:

• trimming
• adjusting the sensitivity of the knobs
• channel reverse
• limitation of steering gear costs
• mixing
• other functions

Trimming is a very important thing. If you release the transmitter handles while driving the model, the springs will return them to the neutral position. It is quite logical to expect that the model will move straight. However, in practice this is not always the case. There are many reasons for this. For example, if you are launching a newly built aircraft, then you may incorrectly take into account the torque from the engine, and in general the model is rarely perfectly symmetrical and correct in shape. As a result, even if the rudders appear to be level, the model will still not fly straight, but in some other way. To correct the situation, the position of the steering wheels will need to be adjusted. But it is quite clear that doing this directly on the model during launches is very impractical. It would be much easier to slightly move the transmitter handles in the desired directions. This is exactly why trimmers were invented! These are small additional levers on the sides of the joysticks that set their displacement. Now, if you need to adjust the neutral position of the rudders on the model, you just need to use the desired trimmer. Moreover, what is especially valuable is that trimming can be carried out right on the go, during launches, observing the reaction of the model. If you find that initially the model does not need trimming, consider yourself very lucky.

Adjusting the sensitivity of the knob is a completely understandable function. When you set up controls for specific model, you need to set the sensitivity so that the control is most comfortable for you. Otherwise, the model will respond to the transmitter knobs too sharply or, on the contrary, too sluggishly. More “advanced” models allow you to set an exponential sensitivity function for the transmitter knobs in order to more accurately “steer” with slight deviations.

If we now think back to the model, we will find that depending on how the steering gears are installed and how the linkages are connected, we may need to change their direction of operation. To achieve this, all transmitters allow independent reversal of control channels.

The mechanics of the model itself may have limitations, so sometimes it is necessary to limit the stroke of the steering gears. For this purpose, many transmitters have separate function travel restrictions, although in its absence you can try to get by by adjusting the sensitivity of the handles.

Now it's time to touch more difficult moments and tell you what mixing is.

Sometimes it may be necessary for the steering wheel on a model to be controlled simultaneously from several transmitter handles. A good example can serve as a flying wing, where both ailerons control the height and roll of the model, i.e. the movement of each depends on the movement of the altitude stick and roll stick on the transmitter. Such ailerons are called elevons:

When we control the height, both elevons deflect simultaneously up or down, and when we control the roll, the elevons work in antiphase.

The elevon signals are calculated as a half-sum and half-difference of the altitude and roll signals:

Elevon1 = (height + roll) / 2
Elevon2 = (height - roll) / 2

Those. The signals from the two control channels are mixed and then transmitted to the two execution channels. Such calculations, which involve input from multiple control knobs, are called mixing.

Mixing can be implemented both in the transmitter and on the model. And the implementation itself can be either electronic or mechanical.

Especially for beginners (with the exception of helicopter pilots), I would like to note that the models you will start with will most likely not require mixers for their operation. Moreover, you may not need mixers for very long (or maybe you will never need them at all). So if you decide to buy yourself a simple 4-channel joystick equipment, or 2-channel pistol equipment, then you shouldn’t be upset about the missing mixers.

You'll find a ton of other features in good transmitters in the upper price range. The extent to which they are needed for a particular model is a debatable issue. To get an idea about them, you can read the descriptions of such transmitters on the manufacturers’ websites.

Analog and computer transmitters

To understand the difference between analog and computer transmitters, let's look at a more realistic example. About fifteen years ago, programmable phones began to spread. They differed from the usual ones in that, in addition to conversation and identifying the number of the calling subscriber, they made it possible to program one button to dial an entire number, or create a “black list” of subscribers to whose calls the phone did not respond. A bunch of additional services, which a simple subscriber often did not need. So, an analog transmitter is like a simple telephone. It usually has no more than 6 channels. As a rule, the simplest of the services described above are implemented: there is channel reversal (sometimes not all), trimming and sensitivity adjustment (usually for the first 4 channels), setting the extreme values ​​of the gas channel (idle speed and maximum speed). Adjustments are made using switches and potentiometers, sometimes using a small screwdriver. Such devices are easy to learn, but their operational flexibility is limited.

Computer equipment is characterized by the fact that all settings can be programmed using buttons and a display in the same way as on programmable phones. There can be a lot of services here. The main ones worth noting are the following:

1. Availability of memory for several models. Very convenient thing. You can remember all the settings for mixers, reverses and rates, so you don’t have to rebuild the transmitter when you decide to use it with another model.
2. Memorizing trim values. Very convenient function. You don't have to worry that the trimmers will accidentally get knocked down during transportation and you'll have to remember their position. Before starting the model, it will be enough just to check that the trimmers are installed “in the center”.
3. A large number of built-in mixers and operating mode switches will allow you to implement the most various functions on complex models.
4. The presence of a display makes it much easier to configure the equipment.

The number of functions and price of computer equipment varies quite widely. Specific Features It’s always best to look at the manufacturer’s website or instructions.

The cheapest devices may come with a minimum of functions and are focused primarily on ease of use. These are primarily model memory, digital trimmers and a couple of mixers.

More complex transmitters usually differ in the number of functions, expanded display and additional modes data encoding (to protect against interference and increase the speed of information transfer).

Top models of computer transmitters have graphic displays large area, in some cases even with touch control:

It makes sense to buy such models for ease of use or for some particularly tricky functions (which may only be needed if you want to seriously engage in sports). Sophistication leads to the fact that top models already compete with each other not in the number of functions, but in ease of programming.

Many computer transmitters have replaceable modules model settings memory, which allows you to expand the built-in memory, as well as easily transfer model settings from one transmitter to another. A number of models provide for changing the control program by replacing special board inside the transmitter. In this case, you can change not only the language of the menu prompts (the authors have not encountered Russian, by the way), but also install a more recent one in the transmitter software with new possibilities.

It should be noted that flexibility in the use of computer equipment also has negative features. One of the authors recently gave his mother-in-law a programmable phone, so she tinkered with programming it for a week and returned it with a request to buy her a simple, as she says, “normal phone.”

Principles of radio signal generation

Now we will move away from the problems of modeling and consider issues of radio engineering, namely, how information from the transmitter gets to the receiver. For those who do not really understand what a radio signal is, you can skip this chapter, paying attention only to the important recommendations given at the end.

So, the basics of model radio engineering. In order for the radio signal emitted by the transmitter to carry useful information, it undergoes modulation. That is, the control signal changes the parameters of the radio frequency carrier. In practice, control of the amplitude and frequency of the carrier, denoted by the letters AM (Amplitude Modulation) and FM (Frequency Modulation), has been used. Radio control uses only discrete two-level modulation. In the AM version, the carrier has either a maximum or zero level. In the FM version, a signal of constant amplitude is emitted, either with a frequency F, or with a slightly shifted frequency F + df. The FM transmitter signal resembles the sum of two signals from two AM transmitters operating in antiphase at frequencies F and F +df, respectively. From this it can be understood, even without delving into the intricacies of radio signal processing in the receiver, that under the same interference conditions, an FM signal has fundamentally greater noise immunity than an AM signal. AM equipment is usually cheaper, but the difference is not very large. Currently, the use of AM equipment is justified only in cases where the distance to the model is relatively small. As a rule, this is true for car models, ship models and indoor aircraft models. In general, you can fly using AM equipment only with great caution and away from industrial centers. Accidents are too expensive.

Modulation, as we have established, allows useful information to be superimposed on the emitted carrier. However, radio control uses only multi-channel information transmission. To do this, all channels are compressed into one through coding. Currently it is only used for this pulse width modulation, denoted by the letters PPM (Pulse Phase Modulation) and pulse-code modulation, denoted by the letters PCM (Pulse Code Modulation). Due to the fact that the word "modulation" is used to refer to coding in multi-channel radio control and to superimpose information on the carrier, these concepts are often confused. Now it should become clear to you that these are “two big differences", as they like to say in Odessa.

Let's consider a typical PPM signal of five-channel equipment:

The PPM signal has a fixed period length T=20ms. This means that information about the positions of the control knobs on the transmitter reaches the model 50 times per second, which determines the speed of the control equipment. As a rule, this is enough, since the pilot’s reaction speed to the model’s behavior is much slower. All channels are numbered and transmitted in numerical order. The value of the signal in the channel is determined by the time interval between the first and second pulse - for the first channel, between the second and third - for the second channel, etc.

The range of changes in the time interval when moving the joystick from one extreme position to another is defined from 1 to 2 ms. A value of 1.5 ms corresponds to the middle (neutral) position of the joystick (control stick). The duration of the interchannel pulse is about 0.3 ms. This structure PPM signal is standard for all manufacturers of RC equipment. The average handle position values ​​may differ slightly from one manufacturer to another: 1.52 ms for Futaba, 1.5 ms for Hitec and 1.6 for Multiplex. The range of variation for some types of computer transmitters can be wider, reaching from 0.8 ms to 2.2 ms. However, such variations allow the mixed use of hardware components from different manufacturers operating in PPM encoding mode.

As an alternative to PPM coding, PCM coding was developed about 15 years ago. Unfortunately, various manufacturers RC equipment could not agree on a single format for the PCM signal, and each manufacturer came up with its own. More details about the specific formats of PCM signals from equipment from different companies are described in the article “PPM or PCM?”. The advantages and disadvantages of PCM coding are also given there. Here we will only mention the consequence various formats: In PCM mode, only receivers and transmitters from the same manufacturer can be used together.

A few words about the designations of modulation modes. Combinations of two types of carrier modulation and two coding methods give rise to three options for equipment modes. Three because amplitude modulation It is not used in conjunction with pulse code - there is no point. The first has too poor noise immunity, which is the main purpose of using pulse-code modulation. These three combinations are often referred to as: AM, FM and PCM. It is clear that in AM - amplitude modulation and PPM coding, in FM - frequency modulation and PPM coding, but in PCM - frequency modulation and PCM coding.

So now you know that:

• the use of AM equipment is justified only for car models, ship models and indoor aircraft models.
• Flying using AM equipment is only possible with great caution and away from industrial centers.
• You can use hardware components from different manufacturers operating in PPM encoding mode.
• In PCM mode, only receivers and transmitters from the same manufacturer can be used together.

Modular expansion

Modular transmitters are produced mainly in remote control versions. In this case, there is a lot of space on the remote control panel where you can place additional knobs, toggle switches and other controls. Among other cases, we will mention a module for controlling a twin-engine boat or tank. It is installed instead two-axis joystick and is very similar to the clutch levers of a crawler tractor. With its help you can deploy the following models on a patch:

Now we will explain how channels are compacted with a modular expansion of their number. Various manufacturers modules are produced that allow up to 8 proportional or discrete additional channels to be transmitted over one main channel. In this case, an encoder module with eight knobs or toggle switches is installed in the transmitter, occupying one of the main channels, and a decoder with eight proportional or discrete outputs is connected to the receiver in the slot of this channel. The principle of compaction comes down to sequential transmission through this main channel of one additional channel in every 20 millisecond cycle. That is, information about all eight additional channels It will get from the transmitter to the receiver only after eight signal cycles - in 0.16 seconds. For each decompressed channel, the decoder produces an output signal as usual - once every 0.02 seconds, repeating the same value eight times. From this it can be seen that compacted channels have much lower performance and it is inappropriate to use them to control fast and important functions model control. In this way, you can create 30-channel equipment sets. What is this for? As an example, here is a list of functions of the lighting and signaling module of a copy of a mainline tractor:

• parking lights
• High beam
• Low beam
• Spotlight Finder
• Stop signal
• Reverse gear (two latest features are triggered automatically from the gas control position)
• Left turn
• Right turn
• Cabin lighting
• Klaxon
• Flashing Light

Modular transmitters are more often used by copyists, for whom the spectacular behavior of the model, the realism of how it looks, and not its dynamics of behavior are more important. Available for modular transmitters a large number of various modules for specific purposes. We will only mention here the aileron trimming unit for aerobatic models. Unlike monoblock transmitters, where control parameters in the “flaperon” modes, the air brake (in our opinion “crocodile”, and in the West “butterfly”) and differential deviation are programmed in the menu, here each parameter is displayed on its own knob. This allows you to make adjustments directly in the air, i.e. without taking his eyes off the flying model. Although this is also a matter of taste.

Transmitter device

The radio control equipment transmitter consists of a housing, controls (joysticks, knobs, toggle switches, etc.), an encoder board, an RF module, an antenna and a battery. In addition, the computer transmitter has a display and programming buttons. Explanations on the body and controls were given above.

The encoder board contains all low frequency circuit transmitter. The encoder sequentially polls the position of the controls (joysticks, knobs, toggle switches, etc.) and, in accordance with it, generates channel pulses of the PPM (or PCM) signal. All mixing and other services (exponent, stroke limitation, etc.) are also calculated here. From the encoder, the signal goes to the RF module and the trainer connector (if there is one).

The RF module contains the high-frequency part of the transmitter. The questioner is assembled here crystal oscillator, which determines the channel frequency, frequency or amplitude modulator, amplifier-output stage of the transmitter, antenna matching circuits and filtering out-of-band emissions. In simple transmitters, the RF module is assembled on a separate printed circuit board and is located inside the transmitter housing. In more advanced models, the RF module is housed in a separate housing and is inserted into a niche on the transmitter:

In this case, there is no replaceable quartz, and the radio signal carrier is formed by a special frequency synthesizer. The frequency (channel) at which the transmitter will operate is set using switches on the RF unit. Some top transmitter models can set the synthesizer frequency directly from the programming menu. Such capabilities make it possible to easily carry pilots to different channels in any combination of races and rounds of competition.

Almost all radio control transmitters use a telescopic antenna. When unfolded it is quite effective, and when folded it is compact. In some cases, it is possible to replace the standard antenna with a shortened helical antenna, produced by many companies, or with a homemade one.

It is much more convenient to use and more durable in the hustle and bustle of competition. However, due to the laws of radio physics, its efficiency is always lower than that of a standard telescopic one, and it is not recommended for use for flying models in complex interference environments in large cities.

During use, the telescopic antenna must be extended to its full length, otherwise the communication range and reliability drop sharply. With the antenna folded, before flights (races), the reliability of the radio channel is checked - the equipment should work at a distance of up to 25-30 meters. Folding the antenna usually does not damage the operating transmitter. In practice, there have been isolated cases of the RF module failing when folding the antenna. Apparently they were due low-quality components and could have happened with the same probability regardless of the folding of the antenna. And yet, the telescopic antenna of the transmitter does not radiate the signal well in the direction of its axis. Therefore, try not to point the antenna at the model. Especially if it is far away and the interference environment is bad.

Most even simple transmitters a “trainer-student” function is provided, allowing a novice pilot to be trained by a more experienced one. To do this, two transmitters are connected with a cable through a special “trainer” connector. The trainer's transmitter is switched on to the radio signal emission mode. The student's transmitter does not emit a radio signal, but the PPM signal from his encoder is transmitted via cable to the trainer's transmitter. The latter has a “trainer-student” switch. In the “trainer” position, a signal about the position of the trainer transmitter handles is transmitted to the model. In the "student" position - from the student transmitter. Since the switch is in the hands of the trainer, he takes over control of the model at any moment and thereby protects the beginner, preventing him from “making wood.” This is how flying model pilots are taught. The trainer connector contains the output of the encoder, the input of the trainer-student switch, ground, and the power control contacts of the encoder and the RF module. On some models, connecting the cable turns on the encoder's power while the transmitter's power is off. In others, shorting the control contact to ground turns off the RF module when the transmitter power is turned on. In addition to the main function, the trainer connector is used to connect the transmitter to a computer when used with a simulator.

The power supply for the transmitters is standardized and is supplied from a nickel-cadmium (or NiMH) battery with a nominal voltage of 9.6 volts, i.e. from eight cans. The battery compartment in different transmitters has different size, which means that the finished battery from one transmitter may not fit another in size.

The simplest transmitters can use ordinary disposable batteries. For regular use it's ruinous.

Top models of transmitters may have additional components useful to the modeler. Multiplex, for example, in its 4000 model integrates a panoramic scanning receiver, which allows you to see the presence of emissions in the frequency range before flights. Some transmitters have a built-in (with remote sensor) tachometer. There are options for a coaching cable made on the basis of optical fiber, which galvanically decouples the transmitters and does not create interference. There are even means of wirelessly connecting a trainer with a student. On many computer transmitters There are replaceable memory modules where information about the model settings is stored. They allow you to expand the set of programmed models and transfer them from transmitter to transmitter.

So now you know that:

• by replacing quartz, you can change the channel of the equipment within the operating range
• By replacing the replaceable RF module, it is easy to switch from one band to another.
• RF modules are designed to work with only one type of modulation: amplitude or frequency.
• During use, the telescopic antenna must be extended to its full length, otherwise the communication range and reliability drop sharply.
• Folding the antenna does not damage the operating transmitter.

Conclusion

After reading brief introduction On the topic of radio control equipment transmitters, you have roughly imagined which transmitter you need. However, the variety of market offers does not make the problem of choice easier, especially at the beginning of radio modeling. Let us give you some advice on this matter.

The radio control transmitter is the most enduring part of all things modeling. It is in the hands of the pilot, and does not rush around at terrible speed, trying to injure those around him and the model itself with all its contents. If you do not reverse the polarity of the transmitter battery, do not step on it or drop it on the floor, then it can faithfully serve for years and decades. If you are engaged in modeling not alone, but together with a close friend, you can generally purchase one transmitter for two. Since the transmitter is a durable component, it is better to purchase a good device right away. It won't be cheap, but it will cover your growing needs over time, and you won't have to sell it a year later for half the price because it's missing any mixers or other features. But you shouldn’t go to extremes and immediately buy a device in the upper price range. The transmitters for champion athletes contain capabilities that will take years to understand and use. Think about whether you need to pay extra money for prestige.

According to the authors' experience, the quality of transmitters depends on their price group. Apparently, at manufacturing plants, more expensive models are more strictly controlled both during assembly and at the stage of purchasing components. An unprovoked failure of a transmitter is generally an extremely rare thing, but in expensive models- almost never found.

For expensive transmitters, special aluminum cases are produced that are used for storage and transportation to the airfield. For cheaper devices, you can purchase a special plastic box, or make it yourself. Such special packaging should not be neglected by those who regularly (weekly) go on flights or races. It will more than once save your favorite transmitter from shock and destruction, which has served you for many years and may be inherited by your son.

Adjustments in radio receivers .

In radio receiving devices, with the help of adjustments, the required operating modes of individual circuit elements are established and maintained, providing both best conditions receiving a useful signal and converting it into information.

All types of adjustments can be divided into two main groups:

Adjustments that change the seme parameters, forming the frequency and phase characteristics of the receiver;

Adjustments that provide the required operating modes of the receiver elements.

The first group includes tuning to a given frequency or tuning to an operating frequency within certain limits. Adjusting the selective properties of the receiver and its bandwidth, setting certain phase relationships.

The second group includes setting the specified electrical modes of active devices (transistors and lamps), setting the modes of individual components, adjusting the gain of the receiving path, and matching individual circuit elements. Depending on the intended purpose, the listed adjustments are divided into production, technological and operational. The first are carried out during the production process or during the repair process. These include adjusting the circuits with trimming capacitors or coil cores, adjusting filters, setting the required voltages on the electrodes, matching feeder lines, etc.

Operational adjustments can be either manual or automatic.

The main ones are:

Adjusting the receiver tuning frequency;

Selectivity adjustment;

Gain adjustment.

Frequency adjustment.

Frequency adjustment includes pre-tuning to the nominal frequency of the received signal and adjustment during operation.

The receiver can be tuned both by the reference generator and by the received useful signal. The number of tunable elements is determined by the receiver circuit and frequency range. Tuning to a given frequency can be either smooth within the operating range of the receiver, or fixed, ensuring the installation of a finite number of frequencies.

Tuning can be carried out either manually or using an electromechanical drive, with fixation of pre-set operating frequencies. In superheterodyne receivers of the centimeter and millimeter ranges, the preselector is in most cases wideband and the receiver is tuned by setting the local oscillator frequency. In a klystron local oscillator, this can be done by mechanically adjusting the resonator, or by changing the voltage on the reflector.

When using quartz local oscillator frequency stabilization in receivers, tuning is carried out either by changing quartz crystals or by using several quartz oscillators that provide a grid of stable frequencies in a given range.

In superheterodyne receivers with a tunable preselector, the tuning of the UHF and local oscillator circuits is coupled. Changing frequencies during tuning should ensure a constant intermediate frequency.

In most cases, circuit adjustment is carried out using variable capacitors, structurally combined into one unit. Depending on the type of receiver and its purpose, the capacitors can be air or film dielectric, discrete capacitors or varicaps.

Variable capacitors have a sufficient coefficient of coverage of the range of capacitances, high quality factor and linearity of capacitance change. The disadvantages are the rather large dimensions of the tuning unit, the complexity of the design with a large number of simultaneously tunable circuits, and the long tuning time.

When using a block of variable-capacitance capacitors, the parameters of the individual elements of the block are approximately the same; the overlap coefficients of the capacitance and, consequently, the frequency range will be approximately the same. However, these capacitors do not provide a constant frequency difference in the converters of superheterodyne receivers.

At intermediate frequency f etc=f G-f With the range overlap coefficients must be different.

With the same overlap coefficient, the difference between the tuning frequencies of the UHF and local oscillator circuits will be in range, since the UHF circuits will be detuned relative to the signal frequency. This will lead to a decrease in gain, which decreases the more the wider the amplifier bandwidth.

To eliminate this drawback, the circuit settings are paired. One of the pairing options is to introduce additional capacitors into the local oscillator circuit.

Inductance L G L is selected such that in the middle of the range both circuits have a difference in tuning equal to f etc. Capacitors are selected as follows: C V » C min , and C A « C Max . In this case, on low frequencies « C operating range when C = C capacitor capacity C A Capacitors are selected as follows: C does not matter, but the capacitance of the capacitor C decreasing the resulting capacitance of the oscillatory circuit increases it resonant frequency

and therefore the local oscillator frequency, bringing the frequency difference closer to the intermediate frequency value. A discrete capacitor is a store of capacitors constant capacity

with series-parallel connection of groups. The use of these capacitors reduces the tuning time, which is primarily determined by the speed of the control circuit and the switch itself. Displaced options are possible when discrete capacitors and discrete inductors are used simultaneously to rearrange oscillatory systems.

The main disadvantage of tuning using discrete capacitors is the limited number of settings and the complexity of the switching circuits.

In relatively low-power cascades, a varicap is used as a frequency-tuning element, which is practically inertia-free in changing capacitance and requires a low-power source of control voltage. The use of varicaps allows you to automate the setup process.

A significant disadvantage of a varicap is the significant nonlinearity of its characteristics, which improves the selective properties of the receiver. One option to reduce the influence of the nonlinearity of the characteristic is to increase the bias voltage applied to the diode. It is possible to include an additional linear capacitor in the capacitive part of the circuit, but this reduces the frequency range coverage coefficient.

In this case, thanks to compensation of even current harmonics, the influence of nonlinearity of characteristics is reduced. In this case, it is necessary to ensure symmetry of the shoulders by selecting varicaps according to the parameters.

Tuning by changing inductance is carried out using variometers or discrete inductors. In the first case, mechanical movement of the coil core inside its frame or closing of part of the turns using a current collector is used. In this case, the overlap coefficient is about 4÷5. However, it must be taken into account that simultaneously with a change in the inductance of the coil, its quality factor also changes, and the tuning mechanism itself is quite complex and cumbersome, which limits the number of simultaneously tunable circuits. The use of a discrete inductor allows for electronic tuning, which is similar to tuning with a discrete capacitor, but is even more cumbersome.

In professional microwave receivers, a non-tunable input and switched filters are used. With a non-tunable wideband preselector, the antenna, UHF and frequency converter are matched using wideband transformers, and tuning is achieved using local oscillator tuning.

In practice, the filter method of tuning a receiver is widely used, in which the entire range of operating frequencies is covered by a number of non-tunable filters, the bandwidth of which is selected with a margin for mutual overlap. The number of filters is determined by the selectivity requirement of the receiver and is limited by the complexity of the control circuit.

Thus, to receive signals in the frequency range, it is necessary to perform a number of operations, including switching the corresponding circuits, switching antennas, etc.

An important step in the operation of any receiving device is fine tuning to the operating frequency, which includes setting the required local oscillator frequencies (there may be several of them in professional receivers) and adjusting the resonant preselector circuits to the signal frequency. When working using frequency synthesizers in the local oscillator, it is possible to tune relatively easily within a short period of time. However, it is more difficult to quickly adjust the preselector by switching on the desired sub-range and adjusting the resonant circuits. In this case, various switching circuits are used, the elements of which are required to have a high contact resistance for the switched current in the open state and a minimum in the closed state. They must also have a small throughput capacitance between the contacts at the operating frequency. In selective circuits, switching is carried out by mechanical or electrical elements.

Reed switches are sealed and magnetically controlled contacts made of a soft magnetic alloy. The capsule is filled with inert gas or evacuated. When the capsule is introduced into a magnetic field, the petals close, and when the field strength weakens, they open due to their own elasticity. The magnetic field is created by a special control coil.

Switching diodes with electronically controlled have high resistance at reverse bias voltage and have low differential resistance at forward bias current.

Adjusting the receiver bandwidth.

The selective properties of the receiver are usually ensured during its design, but in some cases such a need arises during operation. So, in receivers of connected radio links, this makes it possible to weaken the influence of interfering stations neighboring in frequency.

Adjustment can be carried out discretely or smoothly and, as a rule, manually. The adjustable elements can be selective systems of the linear part of the receiving path, mainly in the amplifier, as well as in low-frequency cascades.

To smoothly adjust the passband in the amplifier path, adjustable filters are used, which are a system of two tunable circuits connected to each other using a quartz resonator and are the load of one of the amplifier stages. Thus, when changing the detuning of the circuits, you can adjust the passband, since when they are tuned to an intermediate frequency, the passband is maximum, and when detuned, it narrows. The limits of bandwidth adjustment are determined by the allowable gain losses.

In receivers that have concentrated selection filters in the IF path, selectivity is adjusted by switching filter elements while maintaining the rectangularity of the resonant characteristic within certain limits.

In the post-detector part of the receiver, the bandwidth is adjusted by changing the frequency response in the region of high and low frequencies (timbre control). Passive tone controls are included in the amplifier's input circuit. A regulator that reduces the gain in the high-frequency region is connected in parallel to the input circuit of the amplifier and is represented in the following form.

The values ​​of R p and C are chosen much larger than the similar input parameters of the amplifier. At R p =0, the decrease in frequency response is practically determined by the time constant τ = c R y. If R p ≠0 the decline will only be up to frequency f 1 , after which the resistance Χ c =1/ωc becomes significantly less than R p and does not affect the resulting resistance of the circuit with R p. The frequency response does not change until the frequency, after which it decreases due to the capacitance Cy. A passive tone control that increases the gain in the low-frequency region has the following form and works similarly to the R f C f circuit.

Gain adjustments in the RPU.

For a given amplification stage circuit, K 0 =p 1 p 2 SR e, where p 1 and p 2 are the corresponding switching coefficients, S is the slope of the collector characteristic of the transistor, R e is the equivalent load resistance, taking into account the shunting of the circuit by the transistor and the load. The gain can be adjusted by changing any value included in this expression. When choosing control methods, it is necessary to obtain a significant change in K 0 from the control voltage, a small control current, and a small dependence of other amplifier parameters when the gain changes.

Adjusting the gain by changing the slope of the characteristic.

This adjustment is carried out by changing the operating mode of the active element, so it can be considered modal. In this case, it is necessary to change the bias voltage on the control electrode, which will lead to a change in the slope at the operating point (in a bipolar transistor, in addition to S, q input and q output change). The regulating voltage can be supplied to both the base circuit and the emitter circuit.

In this circuit, the bias voltage at the E-B junction will be U eb =U 0 -E ρ.

As E ρ U increases, the eb decreases, which will lead to a decrease in the collector current I k0 and S k, and as a consequence, a decrease in K 0. The gain control circuit must provide a current in this circuit approximately equal to I 0e, which means that I ρ must be relatively large. It is preferable to supply E ρ to the base circuit when U eb =U 0 -E ρ.

The adjustment current I ρ =I g is I g ≈(5÷10)I 0b and is small. This circuit provides less stability due to the absence of a resistor in the emitter circuit, because its presence will lead to a decrease in the adjustment effect. Otherwise, it is necessary to increase E ρ.

Adjustment by changing R e

can be carried out in various ways.

By including a diode in the circuit.

When E ρ >U k the diode is closed and does not bypass the circuit. R e and K 0 are large.

At E ρ

Adjustment by changing switching factors.<|U 0 | диоды Д 1 и Д 2 открыты, а Д 3 закрыт. Коэффициент передачи максимален. По мере увеличения E ρ динамическое сопротивление диодов Д 1 и Д 2 увеличивается, а Д 3 – уменьшается, The voltage from the circuit is supplied to the divider Z 1 Z 2. By changing one of the resistances you can change p 1. The adjustment circuit for p 2 is similar. Coils with variable inductance or capacitors with variable capacitance can be used as resistances. However, this cannot avoid contour detuning. The best results are obtained by using an attenuator with a variable gain connected between the stages. Adjustable dividers, capacitive dividers on varicaps, and bridge circuits are used as an attenuator.

When |E ρ |

reducing the attenuator gain.

It is possible to use a field-effect transistor as a controlled resistance when the resistance of its channel changes under the influence of E ρ.

Attenuators based on pin diodes, which have a large range of resistance changes and low capacitance, are widely used. The operation of pin diodes is controlled by changing the bias in the transistor base circuit. At zero voltage, adjustments D 1 and D 2 are closed, and D 3 is open (attenuation is minimal). When E ρ is maximum, D 1 and D 2 are open, D 3 is closed (attenuation is maximum). Adjustment

K 0

In the post-detector part of the receiver, the methods for adjusting K 0 are similar to resonant amplifiers. Smooth potentiometric gain control is more often used, and in broadband amplifiers it is usually used in low-impedance circuits. In wideband stages, gain control is often used using adjustable feedback.

An adjustable voltage divider is used to change the constant voltage at the base.

Gain adjustment is carried out by changing the alternating current resistance in the emitter circuit, as a result of which the depth of feedback and the cascade gain change.

The voltage is supplied to the other stage through a controlled divider. Z 2 includes the input impedance of the subsequent stage.

Automatic gain control (AGC).

AGC is designed to maintain the output signal level of the receiving device or amplifier near a certain nominal value when the input signal level changes. The use of AGC is necessary because the input signal level can change quite quickly and chaotically, which cannot be responded to using manual adjustment.

There are many reasons for changes in the input signal level:

Changing the distance between the radiation source and the receiver;

Changes in radio wave propagation conditions;

Changing the receiver from one station to another;

Changing the mutual direction of the receiving and transmitting antennas; etc.

In radar receivers, to the listed reasons one can add fluctuations in the effective reflective surface of the target, changes in targets with different effective surfaces, and random changes in the polarization of received waves.

Ideally, the receiver output voltage should remain constant after reaching a certain output voltage value that ensures normal operation of the terminal device. In this case, the gain must change according to the law

K=U out min /U in at U in ≥ U in min

AGC circuits are built according to two principles: “backward” adjustment and “forward” adjustment. Otherwise, they are also called reverse and direct. Inverse AGC systems (systems with feedback) in them, the point of pickup of the voltage that forms the regulating action is located further from the receiver input than the point of application of the regulating action.

In direct AGC systems, the point at which the AGC trigger voltage is picked up is located closer to the receiver input than the point at which the control voltage is applied.

Reverse AGC systems cannot ensure complete constancy of U out, since it is an input to the AGC system and must contain information for a corresponding change in the regulatory action. In addition, this system cannot simultaneously provide a large depth of adjustment at U out ≈const and high performance for reasons of stability. At the same time, this system protects from overload all cascades located further from the input than the point of application of the control action.

Direct AGC systems can, in principle, provide ideal control when U out ≈const with U in ≥ U in min and arbitrarily high speed. In reality, this is not feasible, since the degree of constancy of the output voltage is determined by the specific data of the elements of the AGC circuit and receiver circuits, subject to technological variations in parameters, time and mode changes. When using this AGC system, cascades located further than the point of application of the regulatory influence are protected from overloads.

The AGC system itself is exposed to a signal with a wide dynamic range, is subject to overload and must contain its own feedback. This system itself turns into a separate receiver channel with a rather complex circuit.

In practice, inverse AGC systems are more widely used, and it is possible to use combined AGC systems.

The block diagram of reverse AGC can be presented as follows

The control voltage is supplied to the amplifier from the output side. The AGC detector ensures that E ρ is proportional to the output voltage, i.e. E ρ =K d U out. The AGC filter filters out the components of the modulation frequencies. This scheme is called a simple AGC. Before or after the detector, an amplifier can be turned on in the AGC circuits, and then the AGC is considered amplified.

The block diagram of a direct simple AGC includes the same elements.

The functional diagram of the combined AGC includes the following elements.

The reverse AGC system is formed by the detector D ARU1, filter F 1 and all cascades of the main path located between the input point of the control voltage U ρ1 and the output of the high frequency unit (HFB).

The direct AGC circuit includes a detector D ARU2, a filter F 2 and a constant voltage amplifier U ARU2. The regulating voltage U ρ2 is introduced into the UHF and ULF, which may or may not be present. Filters Ф 1 and Ф 2 give the AGC circuits the necessary inertia, due to both the stability of AGC 1 and the lack of demodulation of amplitude-modulated signals in AGC 1 and AGC 2.

There is no need to reduce the gain of weak signals (Uin< U вх мин), не обеспечивающих номинального выходного напряжения при максимальном усилении всех каскадов. Для придания цепям АРУ пороговых свойств они запираются принудительным смещением и отпираются тогда, когда напряжение входного сигнала превысит напряжение запирания. Как правило напряжения запирания (задержки) подаются на детекторы или усилители (На схеме E 31 и E 32).

The delay can be entered based on the average value of the signal or the maximum. AGC circuit 1 does not have a special amplifier and is not an amplified system. AGC 2 system is strengthened, it has a greater depth of regulation and is capable of providing a smaller dynamic range of the output signal.

With a weak signal at the receiver input and maximum gain at its output, noise created by external interference and the receiver's own noise is heard. To eliminate this defect, silent AGC systems are used.