If in the autogenerator with inductive feedback and the oscillatory characteristic, smoothly increase M, then, starting from the critical value of the Mr CR, the amplitude of the stationary oscillation, will grow smoothly.
Such a self-excitation mode is called light.
To obtain a light mode, it is necessary that the oscillatory characteristic leaves from the zero point and had a sufficiently large slope in the area of \u200b\u200bsmall amplitudes. All these requirements are performed using an automatic displacement. When using forced (external) displacement, the oscillating characteristic takes the form:
For fluctuations in this case, a very strong feedback is required (OA line, mutually induction M 1).
After the oscillations were established, the connection can be loosen to the value of m 2, in which the communication line occupies the provisions of the OS. With further, the oscillations of the oscillation link are broken. To restore oscillations of M corresponding to the OA communication line. Such a self-excitation mode is called tough.
Appointments, classification and principles for constructing synchronization systems.
In most cases, the normal functioning of various information transmission systems requires to ensure a certain synchronization of the operation of the transmitting and receiving equipment. This feature is usually assigned to special synchronization systems. Their noise immunity and quality of work of the transmission system as a whole depends on the noise immunity and quality of their work. Synchronization systems are formed on the receiving side Special synchronizing signals, synchronous with the corresponding signals generated on the indispensable side, taking into account the distortion that appeared when the signals are distributed over the transmission channel.
All variety of tasks consisting in front of synchronization systems can be divided into two large class: synchronization of various types of switching devices in order to ensure the time separation of signals (in systems with a temporary separation of channels), synchronization of the operation of receiving and processing devices in order to increase their noise immunity (when taking Signals with random parameters).
Real transmission channels are channels with variable parameters.
The optimal reception of signals with random parameters requires an estimate (measurement) of essential parameters (frequencies, retardation time, phase) of such signals. These measurements are imposed on synchronization systems.
Synchronization systems classified by various features. All practical synchronization tasks in transmission systems can be provided with three synchronization systems: high-frequency, element (clock), group.
The high-frequency synchronization task typically occurs when using dodetector correlation signals. In this case, at the point of reception, it is necessary to obtain samples of high-frequency signals, the frequencies of which at any time should be smooth or close to the frequencies of carrier or subcarriers received signals. In the case of coherent processing, this equality should be performed up to the phase.
The task of the elemental (clock) synchronization is to provide on the receiving side of the fixation of the time boundaries of the elemental signals corresponding to the smallest temporary interval to be fixed formed on the transmitting side. The formation of such signals may be necessary to ensure optimal after detector processing of signals and split signals through its channels.
In analog transmission systems, such elementary signals are usually channel intervals (time intervals allocated for transmission over one channel), and in digital systems - elementary information symbols.
Group synchronization should ensure the configuration of the time boundaries of certain groups, elementary signals, such as words, cycles, frames, etc.
Some systems can simultaneously operate all three specified subsystems.
Synchter signals of high-frequency EI element synchronization usually have a periodic structure. Synchronized signals of group synchronization can, be both periodic and forging random flow. In digital transmission systems with a cyclic and periodic survey, when all three specified types of synchronization can be valid, the frequency of all listed synchronization types can be selected by multiple each other.
For example, each frame (parcel group) contains N 1 words each word consists of N 2 characters, and each symbol lasts only N 3 periods of high-frequency carrier or subcarrier. In this case, all types of synchronization can be performed after the installation is set to frames.
Depending on the values \u200b\u200bof permanent supply voltages, the reinforcement element was supplied to the electrodes, and from the coefficient to 0. C are two self-excitation modes: soft and hard.
In soft self-excitation mode, the operating point A is selected on the linear portion of the amplifying element (Figure 9.1, a), which ensures the initial mode of operation of the amplifying element without cut-off. Under these conditions, self-excitation arises from the lowest changes in the input voltage, always available in real conditions due to fluctuations of charge carriers.
First, the oscillations in the autogenerator are growing relatively quickly. Then due to the nonlinearity of the amplifying element, the growth of the amplitude of oscillations is slowed down, since the voltage at its input falls on the sections of the Wah with an all less static steepness, and this leads to a decrease in the average steepness S cf.and the transmission coefficient To 0s Return circuit.
Figure 9.1 - diagrams explaining self-excitation modes.
The increase in oscillations occurs until the transmission coefficient decreases to one. As a result, a stationary mode will be installed in the autogenerator, which corresponds to a certain amplitude of the output oscillations, and the angle cut-off of the output current 0\u003e 90 °. The frequency of these oscillations is very close to the resonant frequency of the oscillating system. We will pay attention: if the amplifying element had a linear volt-ampere characteristic, the increase in the amplitude of auto-oscillations would have happened to infinity, which is physically impossible. Therefore, in a linear chain, sustainable self-oscillations with a constant amplitude cannot be obtained.
Due to the nonlinearity of the volt-ampere characteristics, the form of the output current of the amplifying element is obtained by non-sinusoidal. However, with a sufficiently large kindness (Q \u003d 50 ... 200) of the oscillatory system, the first harmonic of this current and, therefore, the voltage at the outlet of the autogenerator is almost harmonic oscillations.
9.5 Hard Self-Gulation Mode
In this mode, the displacement voltage is specified so that at low amplitudes of the input voltage, the current through the amplifying item did not pass. Then minor fluctuations arising in the circuit cannot cause current in the output chain, and self-excitation of the autogenerator does not occur. Oscillations occur only when they are quite large initial amplitude, which is not always possible to ensure. The process of occurrence and increases of oscillations with tight mode of self-excitation is illustrated in Figure 9.1, b. It can be seen that with small initial input voltage amplitudes (curve 1) current i out \u003d 0 And self-oscillations do not arise. They occur only with a sufficiently large initial voltage amplitude (curve 2) and quickly increase to the steady value. In the stationary mode, the amplifying element operates with the cut-off corners of the output current<90°.
For ease of operation of the autogenerator, it is more expedient to apply a soft self-excitation mode, since in this oscillation mode it occurs immediately after the power supply is turned on. However, with hard mode of oscillations with a cut-off angle<90° обеспечиваются более высокий КПД автогенератора и меньшие тепловые потери. Поэтому в стационарном режиме автогенератора более выгоден именно режим с малыми углами отсечки выходного тока усилительного элемента.
Stability of work AG
The process of occurrence and establishing oscillations in the autogenerator is conveniently investigated using oscillatory characteristics and feedback lines.
10.1 oscillatory characteristics
They constitute the dependence of the amplitude of the first harmonic of the output current of the amplifying element I M 1. from the amplitude of the input voltage U M Bkh. with unchanged bias U 0 and an open chance of feedback :. These dependences are non-linear and can be obtained experimentally by translating the generator to external excitation mode.
Figure 10.1 - oscillatory characteristics AG.
Figure 10.1 shows three oscillatory characteristics corresponding to different displacement stresses. Characteristic 1 corresponds to the displacement at which the coolness of the volt-amps characteristic is of the greatest value. As the voltage increases U M Bkh. The average steepness drops, and the slope of the characteristic decreases.
Characteristic 2 corresponds to a smaller offset voltage at which the static steepness of the enhancement element at the operating point is less than the maximum steepness. As a result, with an increase in voltage average steepness S cf. grows and only with very large values U M Bkh. Begins to decrease.
The third characteristic corresponds to the case when in the absence of the input signal the current through the amplifying item does not pass. This current, and consequently, the current in the oscillatory circuit appears only at some voltage amplitude U M Bkh.sufficient to unlock the lamp or transistor during the part of the period of high-frequency oscillation.
Feedback lines
These lines determine the dependence of the amplitude U M Bkh., i.e. output voltage of the chain of feedback, from the amplitude of the current I M 1.which is the input current of this chain :.
Insofar as 
and 
Receive
.
It follows that the feedback lines are graphically depicted in the form of direct, emerging from the origin (Figure 10.2). The slope of these direct is different and depends on the value of the coefficient To OS.. The stronger feedback in the autogenerator, the smaller angle of inclination has a feedback line relative to the axis U M Bkh. (Figure 10.2 
).
Figure 10.2 - Feedback line.
10.3 Determination of stationary amplitude of oscillations
In stationary mode AG amplitude input voltage U M Bkh. and corresponding to this amplitude of the first harmonic of the output current I M 1. The enhancement element must simultaneously satisfy both specified dependencies. This is possible only at the intersection points of the oscillatory characteristics and feedback line. In fig. 10.3 Axis of the abscissa oscillatory characteristics U M Bkh. It serves as the axis of the ordinate of feedback lines 2-5, and the scale on them is the same. According to the total axis, the ordinate characteristics 1 and lines 2-5 current is postponed I M 1..
The feedback line 2 corresponding to the rate of transmission of the feedback chain has a total point with an oscillatory characteristic only at the beginning of the coordinates. In this case, self-excitation of the autogenerator does not occur due to the small coefficient To OS. or the small value of the resonance resistance contour R cut.
Figure 10.3 - Determination of the stationary state of AG in soft self-excitation mode.
With a critical coefficient, direct feedback 3 merges with an oscillatory characteristic in the OA region in which it is linear, but does not cross this characteristic. In this case, self-excitation is also missing, which confirms the conclusion: in an autogenerator running in linear mode and having, getting self-oscillations is impossible .
The fluctuations in ag arise only with the coefficient to which the feedback line corresponds to 4. This line under the conditions of a soft self-excitation mode has two common points with a oscillatory characteristic, 0 and q. point in corresponds to the stationary state of the autogenerator characterized by current amplitudes I M 1 Band voltage U M VKW. In this state, the generator comes in the process of self-excitation, but may come out of it under the action of various destabilizing factors.
Consider the processes that will leak at the same time.
Suppose that the voltage at the input of the amplifying element has decreased to the value U M VKS.. This voltage will cause a current generator output circuit I M 1 C (point C in Figure 10.3), which, thanks to the feedback, will increase the voltage at the entrance to U M V.which will lead, according to the characteristics 1, to an increase in current to I M 1 A and so on. As a result, the generator will return to a state-defined point in the intersection of characteristics 1 and 4. Similarly, it can be shown that if under the action of any causes, the voltage at the input of the amplifying element will increase and will become more than U M VKW (Point D in Figure 10.3), the generator will automatically switch to a state defined by the point V. These reasoning confirm that the point B is a point of a stable equilibrium and corresponds to the stationary operating mode of the autogenerator. Voltage and current amplitudes in stationary mode are determined by feedback value. With an increase in feedback (Figure 3, Direct 5), the corresponding stationary amplitudes increase to values U M Vheand I M 1 E.
The second overall point of the oscillatory characteristics 1 and feedback line 4 (Figure 10.3, point 0) is an unstable, since it arised fluctuations regardless of initial amplitudes increases to oscillations with stationary amplitudes defined by the position of the V. point
Figure 10.4 - Determination of the stationary state of AG in hard self-excitation mode.
Under the conditions of a hard mode of self-excitation (Figure 10.4) oscillating characteristics 1 and the feedback line have three common points: O, A, V. Point 0 characterizes the steady state of rest of the autogenerator, i.e., the absence of self-excitation at small initial oscillation amplitudes. Oscillations occur only when the initial input voltage amplitude becomes more U M V.determined by the point A in Fig. 10.4, for example, the voltage increased to the value U M VKS. . Caused by this voltage current I M 1 C Returning with the help of feedback voltage at the input of the generator, which will lead to greater increase in current and so on.
(See Figure 10.4, Lines with arrows). As a result, a steady oscillatory mode is achieved (point B) characterized by amplitudes U M VKW and I M 1 B.
Suppose now that the voltage at the inlet of the generator has become less than U M V. and reached importance U M VKWdetermined by the dot D. The current will decrease to I M 1 Dthat will further reduce the input voltage, as shown by the arrow lines in Fig. 4. As a result of oscillations fucked. Consequently, the point and the intersection of the oscillating characteristic and the feedback line characterizes the unstable state of the autogenerator mode.
Depending on the values \u200b\u200bof permanent supply voltages, which were supplied to the electrodes of the amplifying element, and from the coefficient to the OS are two modes of self-excitation: soft and hard.
1. Imprint soft self-excitation.
In this mode, the operating point A is chosen on the linear portion of the volt-amps characteristics of the amplifying element, which ensures the initial mode of operation of the amplifying element without cut-off the output current i (Fig. No. 2).
Fig. # 2. Chart, soft self-excitation regime.
Under these conditions, self-excitation arises from the most minor changes in the input voltage of U W, always available in real conditions due to fluctuations of charge carriers.
First, the oscillations in the autogenerator are growing relatively quickly. Then due to the nonlinearity of the volt-ampere characteristics of the amplifying element, the growth of the amplitude of the oscillations is slowed down, since the voltage at its input falls on the volt-ampered sections of the total static steepness, and this leads to a decrease in the average steepness SR and the transmission coefficient Communication.
The increase in oscillations occurs until the transmission coefficient to decreases to one. As a result, in the autogenerator, the stationary regime, which corresponds to a certain amplitude of the output oscillations, and the angle of cut-off of the output current 0\u003e 90 0. The frequency of these oscillations is very close to the resonant frequency of the oscillating system.
If the reinforcement element had a linear volt-ampere characteristic, the increase in the amplitude of auto-oscillations would have happened to infinity, which is physically impossible. Therefore, in a linear chain, sustainable self-oscillations with a constant amplitude cannot be obtained.
Due to the nonlinearity of the wax-absorption, the form of the output current I of the amplifier element is inconed. However, with a sufficiently large kindness (50 ... 200) of the oscillatory system, the first harmonic of this current and, therefore, the voltage at the autogenerator's outlet is almost harmonic oscillations.
2. Rigid self-excitation mode.
In this mode, the displacement voltage U 0 is specified so that at low amplitudes of the input voltage, the current through the amplifying item did not pass. Then a slight fluctuations arising in the circuit cannot cause the output circuit current, and the self-excitation of the autogenerator does not occur. Oscillations occur only when they are quite large initial amplitude, which is not always possible to ensure. The process of occurrence and increases of oscillations with tight mode of self-excitation illustrates with the help of Fig .№3.
Fig.№ 3. Chart of hard self-excitation
From the consideration of this figure it can be seen that with small initial amplitudes of the input voltage (curve1), the current I \u003d 0 and auto-oscillations do not occur. They occur only with a sufficiently large initial voltage amplitude (curve 2) and quickly increase to the steady value. In the stationary mode, the amplifying element operates in the corners of the cut-off of the output current 0<90 0 .
For ease of operation of the autogenerator, it is more expedient to apply a soft self-excitation mode, since in this oscillation mode immediately after the power supply is turned on. However, with hard mode of oscillations with a cut-off angle 0<90 0 обеспечиваются более высокий КПД автогенератора и меньшие тепловые потери. Поэтому в стационарном режиме автогенератора более выгоден именно режим с малыми углами отсечки выходного тока усилительного тока усилительного элемента.
Automatic offset. Its use provides the ability to operate the autogenerator at the initial inclusion in soft self-excitation mode with the subsequent automatic transition to rigid self-excitation mode. This is achieved by using a special automatic displacement chain in the autogenerator.
In Fig. No. 4a, a simplified schematic diagram of the autogenerator on a bipolar transistor VT, the load of which is the oscillating circuit of L2C2. A positive feedback voltage is created on the L1 coil and is supplied between the base and emitter of the transistor. The initial offset voltage on the transistor base is created by the source included the R1C1 auto-offset circuit.
The process of the occurrence and increases of oscillations is illustrated with Fig.№ 4b. At the first moment after the generator is turned on, i.e. At the time of the appearance of oscillations, the operating point A is located on the plot of maximum steepness of the Volt-ampere characteristics of the transistor. Due to this, the oscillations occur easily under the conditions of a soft self-excitation regime. As the amplitude increases, the base current increases, the constant component of which creates a voltage drop U cm on the resistor R1 (the variable component of this current passes through the C1 condenser). Since the voltage U cm is applied between the base and the emitter in a negative polarity, the resulting constant voltage on the database U 0 - U cm decreases, which causes the operating point displacement down the characteristic of the transistor and translates the autogenerator to the operating mode of the Cutlery Current Circuit Collectors I K and Base I B have the form of a pulse sequence, and the voltage at the y output, created by the first harmonic of the collector current, is a sinusoidal oscillation with a constant amplitude.
Thus, the automatic displacement circuit R1C1V in the autogenerator acts as a regulator of the self-excitation process and provides the condition of soft self-excitation at the initial moment, followed by the transition to a more advantageous mode with small cut-off corners.
The autogenerator, depending on the conditions, can work in a soft or hard mode of self-excitation. To disclose the peculiarities of these modes of self-excitation, it is convenient to jointly consider the amplitude amplitude of the amplifier with the EOS circuit (actually an amplifier), which always has nonlinearity, and the amplitude characteristic of the loop of the positive OS, which is linear (feedback circuit is a linear four-pole).
In fig. 3.2, but A typical amplitude characteristic of a nonlinear amplifier actually is presented.
With small input signals, the output signal changes in proportion to the input (the amplifier has a constant gain, equal to tangent angle ah to the abscissa axis), at large input signals, the specified proportionality is broken (the amplifier gain coefficient depends on the amplitude of the input signal). The feedback line is a direct conducted at an angle. 
To the abscissa axis, as a linear dependence is observed between the output voltage and voltage of the OS.
At the time of turning on the power of the autogenerator at the inlet of the amplifier, there is noise having a wide spectrum of frequency components, including the component whose frequency corresponds to the resonant frequency of the electoral system. It should be noted that the other spectral components of noise will be suppressed in one way or another by the electoral system. At the output of the amplifier after the strengthening in TO Once the output signal will appear, which, after weakening the chain of the PD, arrives at the amplifier input in the form of voltage. The process will flow until the output oscillation amplitude reaches a stationary value (the balance of amplitudes will be performed).
From fig. 3.2, but it is seen:
point BUTit is a point of sustainable equilibrium;
generation is possible only under such conditions when the feedback line crosses the amplifier's amplitude characteristic, which corresponds to the implementation of the condition.
The mode of self-excitation of the autogenerator considered above is called soft.It is necessary to ensure that AH amplifier came out from zero and had a linear area at the beginning of the coordinates with a sufficient tilt angle to the abscissa axis.
The mild mode of self-excitation of the generator is characterized by the following features:
§ Ah amplifier and direct feedback intersect only at one point, which is a dynamic equilibrium point;
§ oscillations if you change the coefficient β , occur (stopped) with the same coefficient of the village;
§ When the excitation of the autogenerator does not require external influences;
§ With the soft mode of self-excitation of the generator, there is the possibility of setting the specified vibration amplitude by selecting the coefficient POS.
At the same time, it should be noted that the mild mode of operation of the autogenerator is economically unprofitable, since the autogenerator works in linear mode and its KPD. does not exceed 50%.
Despite the specified disadvantage, the soft mode of self-excitation is the main mode of operation of auto-generators.
The process of excitation of oscillations occurs otherwise, if the amplifier has S.- figurative ah (Fig.3.2, b.). When installing the coefficient β < β 2 Ah Amplifier and the PIT line has no intersection points. This means that the coefficient is small, and the autogenerator is not excited.
When installing the coefficient β 1 < β < β 2 Ah Amplifier and the POS line has two intersection points BUT and FROM. This means that the condition of the balance of amplitudes is performed for two values \u200b\u200bof the amplitude of the oscillations of the autogenerator.
Point FROM characterizes the unstable state of the autogenerator. Let at some point in the moment the amplitude at the outlet of the generator corresponds to the point FROMIn this case, the gain of the amplifier itself is equal to TO C. Suppose that under the action of the external factor of the amplitude of oscillations decreased. This will lead to a decrease in the signal at the input of the generator, since U. VK \u003d β · u Out, and will cause further decrease in the amplitude of the output oscillations, since the amplifier amplifier coefficient TO less than TO FROM . The result of external influences in the case under consideration will be a breakdown. On the contrary, if the oscillation amplitude external factor will increase, then the input signal will increase. This will cause a further increase in the amplitude of the output oscillations, which will occur until the system proceeds to a stationary state. .
Point BUT characterizes the steady (stationary) state of the autogenerator, while the gain of the amplifier actually is equal to To A.. Suppose that under the action of an external amplitude factor oscillations corresponding to the point BUT, decreased. This will lead to a decrease in the signal at the input of the generator, since U. VK \u003d β U. Out However, since the amplifier gain coefficient TO In this case, more TO A, the input will receive greater gain and the amplitude of the output signal will increase and will again correspond to the point BUT.
Obviously, to start the auto-generator, the amplitude of the excavating effect should exceed the values \u200b\u200bof the input signal amplitude corresponding to the point FROM. The consisted regime of excitation of the autogenerator is called tough.
In case you establish a coefficient β = β 2 , the autogenerator also works as in soft mode, while there is a point of steady equilibrium.
Consider how the amplitude of oscillations changes if the POS coefficient changes, and there are no external influences.
In accordance with the above, the generator launch will not happen if β < β 2 (line pos β passes left line β 2). Generator starts will not happen and in case β 1 < β < β 2 (line pos β passes between lines β 1.and β 2.), as there is no external electric pushes. The generator will be excited only in the case of β = β 1.This establishes a stationary amplitude of oscillations. If after starting the generator further decrease the coefficient β within β 1 < β < β 2, then breaking the oscillations will not happen, it will only decrease the amplitude of oscillations . The disruption of the oscillations will occur when β = β 2. To resume oscillations, it is necessary to establish a coefficient of β = β 1 .
Thus, the hard mode of the generator self-excitation is characterized by the following features:
§ The gain of the amplifier gain has an inflection point and intersects with a straight PIT in one or two points;
§ There are two values \u200b\u200bof the critical coefficient of POS ( β 1 I. β 2.) corresponding to the launch and breaking of the oscillations of the autogenerator;
§ The amplitude of oscillations even for critical launch β 1 can not be close to zero;
§ It is possible to start the generator when β 1 < β < β 2 Due to the initial external push.
The hard mode of the autogenerator is more economical (the autogenerator has a higher kp.) Than the soft mode, since the amplifier works in nonlinear mode. At the same time, with severe mode it is impossible to obtain fluctuations in small amplitudes, and the generator starts has certain difficulties. The hard mode of self-excitation of auto-generators is rarely applied.
