Design of a radio broadcast transmitter with amplitude modulation. Design of radio transmitting devices - Shakhgildyan V.V.


Name: Design of radio transmitting devices.

The issues of designing radio transmitting devices of various wavelengths and powers are considered. A methodology for calculating connected radio broadcasting and television radio transmitters, as well as radio transmitters for radio relay and space communications. Features of the design of transistor cascades of radio transmitting devices and exciters of various frequency ranges are outlined. The book is intended for students of communications universities, and can also be useful for developers of radio equipment.



Preface. 6
Chapter 1. Introduction
1.1. General information. 7
1.2. Electrovacuum devices for radio transmitting devices. 8
1.3. General recommendations on constructing a block diagram of the tract high frequency transmitter. 16
Bibliography. 19
Chapter 2. Long and medium wave radio transmitters
2.1. Types and purpose of transmitters. 21
2.2. Basic requirements for transmitters. 22
2.3. Structural diagrams. 25
2.4. Calculation of the output circuit system. 33
2.5. Features of the circuit diagrams of the output stage. 36
Bibliography. 41
Chapter 3. Design of shortwave transmitters
3.1. Types of transmitters and requirements for them. 42
3.2. Structural diagrams. 45
3.3. Selecting a mode and calculating a tube resonant amplifier. 52
3.4. Calculation of stability conditions and power gain of resonant cascades. 56
3.5. Broadband amplification stages. 62
3.6. Design of broadband KB range transformers. 70
3.7. Oscillatory systems. 84
3.8. Harmonic filtering. 94
Bibliography. 106
Chapter 4. Calculation of generator modes with amplitude modulation
4.1. A quick introduction to amplitude modulation. 109
4.2. Modulation on the control grid by displacement. 110
4.3. Calculation of amplifiers of modulated oscillations. 113
4.4. Modulation on a pentode grid. 114
4.5. Anode modulation. 115
Bibliography. 121
Chapter 5. Modulators of communication and broadcasting transmitters
5.1. Modulators of communication transmitters. 122
5.2. Modulators for radio broadcast transmitters. 127
5.3. Negative Feedback in modulators. 140
Bibliography. 143
Chapter 6. Single-sideband shortwave transmitters
6.1. General information. 144
6.2. Block diagrams of single-sideband transmitters. 148
6.3. Group signal in the path of a single-sideband transmitter. 149
6.4. The procedure for designing a transmitter with OM. 151
6.5. Technical calculation of the output stage. 156
6.6. Calculation of industrial efficiency of a transmitter with OM. 164
Bibliography. 165
Chapter 7. Design of final stages of transistor transmitters
7.1. Introduction. 167
7.2. Oscillator transistor and its parameters. 168
7.3. Classification of transistor generators. 174
7.4. Generators in under-stressed and critical modes. 178
7.5. Generators in key and overvoltage modes. 194
7.6. Features of the design of intermediate stages. 208
7.7. Features of designing generators with collector amplitude modulation. 209
7.8. Design of communication circuits. 212
7.9. Calculation of thermal conditions. 213
Bibliography. 216
Chapter 8. Pathogens
8.1. Introductory remarks. 218
8.2. Selection and rationale functional diagram reference frequency sensor. 219
8.3. Formation of types of work in the exciter. 226
8.4. Selecting exciter frequencies. 230
Bibliography. 232
Chapter 9. Design and calculation of oscillatory systems of amplifiers of the meter, decimeter and centimeter ranges
9.1. Design features of amplification devices. 234
9.2. Principles of constructing oscillatory amplifier systems. 242
9.3. Oscillatory systems using homogeneous lines. 249
9.4. Oscillatory systems using non-uniform lines. 266
9.5. Communication circuits. 274
9.6. Amplifier power circuits. 292
Bibliography. 294
Chapter 10. Broadcast image transmitters of the VHF and UHF ranges
10.1. General information. 296
10.2. Drawing up a general structural diagram. 297
10.3. Construction and calculation of tetrad cascades of teaching materials. 310
10.4. Construction and calculation of the path of a broadband transistor computer. 320
10.5. Construction and calculation of a path of modulated oscillations at an intermediate frequency. 325
Bibliography. 333
Chapter 11. FM broadcast transmitters and soundtrack television programs
11.1. Basic specifications FM broadcasting and audio transmitters. 334
11.2. Drawing up block diagrams of transmitters. 334
11.3. Design of RF amplification path cascades. 341
11.4. Design of frequency modulators using varicaps. 345
Bibliography. 349
Chapter 12. Klystron transmitters for tropospheric and space communications and television
12.1. Basic technical characteristics of transmitters of tropospheric and space communication lines. 350
12.2. Drawing up structural diagrams. 351
12.3. Selecting the klystron type. 353
12.4. Calculation of electrical and geometric parameters of the klystron. 355
12.5. Amplifier mode calculation. 363
12.6. Verification calculation frequency characteristics. 369
12.7. Gain. Exciter power. 370
12.8. Compilation schematic diagram klystron amplifier. 371
12.9. Design of klystron amplifiers for a television radio station. 373
12.10. Calculation of klystron amplifier transmitter modes, images. 377
12.11. Calculation of the klystron amplifier mode of the audio transmitter. 382
12.12. Construction of a circuit for the final stages of television klystron amplifiers. 384
Bibliography. 386
Chapter 13. Amplifiers and oscillators UHF and microwave on metal-ceramic lamps
13.1. Introductory remarks. 387
13.2. Circuits of amplifiers and self-oscillators. 387
13.3. Calculation of power amplifier mode. 389
13.4. An example of calculating the mode and oscillatory system of an amplifier. 395
13.5. Strengthening modulated oscillations. 406
13.6. Calculation of the oscillator mode. 408
Bibliography. 410
Chapter 14. Radio relay transmitters
14.1. Introductory remarks. 411
14.2. Basic requirements for RRL transmitters with frequency modulation. 412
14.3. Construction of block diagrams of FM RRL transmitters. 415
14.4. Design of frequency modulators using varicaps. 419
14.5. Design of frequency modulators using reflective klystrons. 422
14.6. Design of microwave transmitter mixers. 423
14.7. Calculation of bandpass microwave filters. 426
Bibliography. 426
Appendix 1. 427
Appendix 2.

Electrovacuum devices for transmitting devices.

Radio transmitting devices use a variety of electronic, semiconductor and ionic devices. Their range is constantly updated: fundamentally new ones are developed, existing ones are improved, and outdated ones are removed from practice.

The feasibility of using lamps or transistors and their specific types for each cascade are determined by technical and economic calculations. The general trend at present is as follows.

In powerful cascades of transmitters (with the exception of the longest wavelengths), electronic radio tubes and special electronic microwave devices are mainly used. Semiconductor devices are increasingly being used in low-power cascades.
The use of low-power generator and receiving-amplifier tubes in transmitting devices is justified only if it is proven that it is impossible or clearly inappropriate to use transistors, semiconductor diodes etc. For example, the use of receiving and amplifying lamps turns out to be inevitable in conditions high temperature environment, with a large difference between the maximum and minimum temperatures, in the presence of penetrating radiation, etc.

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Thesis on the topic:

Development of a radio transmitting device operating in single-sideband modulation mode

INTRODUCTION

DESIGN ASSIGNMENT

1. SELECTION AND JUSTIFICATION OF STRUCTURAL DIAGRAM

2. CALCULATION OF THE OPERATING MODE OF THE FINAL CASCADE

2.1 Selecting the transistor type

2.2 Calculation of the transistor input circuit

2.3 Calculation collector circuit final stage

3. CALCULATIONS AND SELECTION OF INPUT CASCADES

3.1 Calculation of a quartz oscillator

3.2 Selecting the type of balanced modulator

3.3 Selection and calculation of filters

4. COMMUNICATION LINE CALCULATION

5. FREQUENCY SYNTHESIZER

6. CALCULATION OF THE COOLING SYSTEM OF THE 2T925V TRANSISTOR

7. POWER SOURCE

CONCLUSION

BIBLIOGRAPHY

APPLICATIONS

INTRODUCTION

The topic of this diploma project is the development of a radio transmitting device operating in single-sideband modulation mode. Radio transmitting devices of this type are widely used in the frequency range f = 1.5 - 30.0 MHz as communications, since the speech (transmitted) signal is quite narrowband - 300... 3400 Hz. This is due to the purpose of this type of transmitters, both in terms of energy consumption (mobile radio stations) and the characteristics of this frequency range, namely its low information capacity.

Based on the above circumstances, we can conclude that single-sideband modulation has a number of advantages over conventional amplitude modulation. These include: a narrower frequency band of the radio channel (which will allow frequency multiplexing of channels), better energy characteristics of radio transmitters (increased efficiency compared to conventional amplitude modulation), versatility (use in stationary conditions as base stations, as well as in systems of mobile services - land, sea, air).

The disadvantage of this type of modulation is the complicated circuit diagram of both the transmitting and receiving paths of this type devices.

The requirements that the transmitter must satisfy are, first of all, simplicity of circuit design (which is achieved by using modern element base), which provides high reliability, the ability to operate in a wide range of ambient temperatures and humidity, ease of use, sometimes shock resistance, low power consumption, and low cost.

DESIGN ASSIGNMENT

Design a communications radio transmitter with single-sideband modulation that satisfies the following parameters:

    Maximum output power in the feeder – P 1 max = 10 W;

    Frequency range – f = 10…16 MHz;

    Feeder characteristic impedance – W f =50 Ohm;

    Power supply voltage – E = 220 V, 50 Hz (mains);

    Frequency grid step – 1 kHz;

    PVI = - 45 dB;

    Modulation frequencies – f mod = 0.3…3 kHz;

    Relative frequency instability – 3 * 10 – 5.

During the design process it is necessary to select and calculate:

– draw up and justify a structural diagram;

– formulate requirements for the power source, provide diagrams.

Graphic works:

– part of the electrical circuit diagram (selected by the teacher);

– diagram of the arrangement of elements of the final cascade (top and side views).

1. SELECTION AND JUSTIFICATION OF STRUCTURAL DIAGRAM

Communication transmitters of this frequency range f = 1.5...30 MHz operate, as a rule, in single-sideband modulation mode. A single-sideband signal is generated by the filter method at a relatively low frequency (f 0 = 500 kHz) and transferred using frequency converters to the operating range.

We will construct the block diagram of the designed transmitter in such a way as to minimize nonlinear distortions while simultaneously ensuring a specified suppression of out-of-band oscillation radiation, as well as a minimum number of tunable circuits in the intermediate and final stages of the transmitter. Let's consider a variant of the structural diagram (Fig. 1), which fully satisfies the requirements stated above.

Rice. 1. Structural scheme the designed transmitter.

Brief description of the proposed block diagram and purpose of the blocks:

The audio signal from the microphone is amplified by a low-pass amplifier (LFA) to the required level and goes to balanced modulator 1 (BM 1), the second input of which receives a voltage with a frequency f0 = 500 kHz (the signal generated by a frequency synthesizer is used as the reference frequency f0 ). The frequency of this generator is selected taking into account the amplitude-frequency characteristics of the electromechanical filter (EMF) and the choice of the working sideband (upper). For this frequency, the industry produces electromechanical filters (EMFs) with an attenuation characteristic slope S = 0.1...0.15 dB/Hz; in addition, the frequency synthesizer will provide the specified relative frequency instability, since it uses a quartz oscillator. Since the useful signal band in accordance with the technical specifications is 300 to 3000 Hz, it is possible to use an EMF whose bandwidth is 3 kHz. According to the standards, for single-sideband transmitters with an operating frequency above 7 MHz, the output signal must contain an upper sideband (Fig. 2), and for an operating frequency below 7 MHz - a lower one. The output of BM 1 produces a two-way signal with a weakened carrier. The degree of suppression of the carrier frequency at the transmitter output is determined by the balanced modulator and the EMF, and the unwanted power supply is determined only by the parameters of the EMF. Therefore, the degree of presence of extraneous spectral components in the signal depends on the quality of construction of this cascade, and in subsequent cascades it is impossible to change the ratio of these components in the signal. After the signal passes through BM 1 and the EMF, the signal fades, so it is advisable to use a compensation amplifier (KU 1), from the output of which the signal goes to BM2.

The second input of BM 2 receives a signal of the auxiliary frequency f 1 = 20 MHz, which, similar to f 0, is generated by the synthesizer. Frequency f 1 is selected above the upper operating frequency of the transmitter – f B . With this choice, the combination frequency at the output of BM 2, equal to f 1 + f 0, will also be higher than the upper frequency of the operating range of the transmitter. Consequently, oscillations of the auxiliary generator f 1 and first-order conversion products with frequencies f 1 + f 0, if they enter the input of the power amplifier, will not create interference in the operating range of the designed transmitter. The relative detuning between the combination frequencies at the output of BM 2 is, as a rule, not large, therefore the selection of the desired combination frequency should be carried out by a piezoceramic filter (PF) or a surface acoustic wave filter, which has a sufficiently high selectivity. The bandwidth of this filter must be no less than the bandwidth of the transmitted signal. After the signal passes through BM 2 and PF, the signal is also attenuated, so here it is also advisable to use a compensating amplifier (KU 2), after which the signal goes to BM3.

The single-sideband signal from the output of KU 2 in the balanced modulator BM3 is mixed with frequency f 2. The source of these oscillations is a discrete frequency grid synthesizer, which generates a grid in a given range with a given step. The frequency f 2 is selected above f 1, that is, above the operating range. The frequencies of the operating range are obtained at the output of BM3 depending on the value of f 2. They are equal to the difference between frequencies f 2 and intermediate conversion frequencies at the output of the bandpass filter f = f 2 - f 1 - f 0. In this way, the required grid range f 2 can be determined.

Upper value: f 2 = f in + f 1 + f 0 = 16 + 20 + 0.5 = 36.5 MHz

Lower value: f 2 = f n + f 1 + f 0 = 10 + 20 + 0.5 = 30.5 MHz

These frequencies are isolated by a low-pass filter (LPF), which must cover the entire operating range. The low-pass filter cutoff frequency must be no less than the upper operating frequency of the range.

A single-sideband signal is generated at a low power level of 1 - 5 mW. It is brought to a given level at the transmitter output by a linear broadband power amplifier, the number of stages in which is determined by the value of the end-to-end gain:

K P = P 1 / P VX = 11.2 / 0.005 = 2240,

where P 1 is the power in the collector circuit of the final stage of the transmitter,

P VX - single-sideband signal power at the output of the low-pass filter.

As a result of amplification of the silo, a sufficiently strong signal is obtained that arrives at the input of the final stage (OC), which determines the nominal specified power in the transmitting path, determines the efficiency of the device, in addition, the communication circuit (CC) connected in series with the OC determines the level of out-of-band emissions. Let us determine the number of amplification stages (AS) to obtain the nominal specified power based on the value of the end-to-end gain:

Let us assume that the power gain of one stage is equal to 8, then the number of silo stages can be determined by dividing K P by the value of the gain of one stage.

The signal power amplification by an amount of at least 4.375 will be carried out in the final stage.


1 . Technical task

Design an AM broadcast transmitter (PRVAM) with the following parameters:

· Power in the antenna (load) P ~ =100 kW;

· Characteristic impedance of the feeder with Ф = 150 Ohm;

· Feeder efficiency z f = 0.80;

· Traveling wave coefficient KBB = 0.8;

· Maximum modulation index m = 1;

· Operating frequency range f min - f max, 0.1 - 0.3 MHz;

· Modulation frequency range DF = 50 10000 Hz;

· carrier frequency f 0 =200 kHz.

Analysis of technical specifications:

Radio broadcast transmitters (PRB) with AM used in the long, medium and short wave ranges must comply in their parameters with GOST 1392468. In tube versions of transmitters to receive an AM signal of a given power, the most common are anode, anode-screen or combined (over several electrodes) modulation in terminal stage, amplification of modulated oscillations (UMO) is less commonly used.

As part of this work, the following calculations were carried out:

· final stage at peak, minimum and telephone points, as well as at 100% modulation depth;

modulating device and electrical parameters its elements; transformer, chokes, blocking capacitors;

· output oscillatory system;

2. Choosing a construction method design of the designed device

For implementation of this device An implementation option with anode modulation was chosen due to its high energy efficiency, good linearity and widespread use in radio broadcast transmitters. The block diagram of the designed device is shown in Figure 1.

Figure 2.1. Block diagram of the projected broadcast transmitter myself.

Approximate calculation of a radio transmitter with AM according to the block diagram

According to the technical specifications, the transmitter must have the following parameters: P ~ = 100 kW;

modulation index m = 1;

operating frequency range f min f max = 0.1 0.3 MHz.

Based on the parameters specified above, we will make an approximate calculation of the elements of the radio transmitter.

The peak power in the antenna will be:

The powers P 1 T and P 1 max supplied by OK devices are determined by the formulas:

where is the approximate efficiency of the output oscillatory system. selected from the table given in and , feeder efficiency.

Then P 1 T = 136 kW, P 1 max = 544 kW.

Due to the fact that anode modulation is implemented in the OK, the rated power of the electric generator is selected according to the rule P 1nom? 2P 1 T = 272 kW (rated power of generator lamps).

Because When developing the OK, a push-pull circuit was used, then P 1nom of the lamp = .

The choice of lamp type is carried out according to such parameters as P 1nom of the lamp and maximum operating frequency f max.

According to the reference tables presented in and, the GU 66 B lamp was selected, having following parameters: E a nom = 10 kV; S = 0.16 A/V, P nom reference = 150 kW.

The description of the GU 66 B lamp is given in Appendix 1.

The schematic diagram of the designed radio broadcast transmitter is shown in Figure 2.2.

Figure 2.2 - Schematic diagram of the designed AM transmitter.

3 . Calculation of the final stage (OK)

At this point, the OK calculation is performed in the following modes:

· at the peak point;

· at the minimum point;

· at a telephone point;

· at 100% modulation depth.

Anode voltage modulation depth m = 1 in accordance with terms of reference.

The schematic diagram of the final stage is shown in Figure 3.1.

Figure 3.1 Schematic diagram of the final stage.

The anode supply voltage for telephone point mode is usually selected as:

The cutoff angle is selected within the range and = 80? - 90?. IN in this case Let's take the cutoff angle equal to 90?.

3 .1 Calculation of the final stage (OK) in maximum point

The calculation of the final stage at the maximum point is carried out according to the method outlined in and.

Anode supply and shielding grid supply voltage:

E a max = E a . t (1+m)=16 kV

Anode voltage utilization factor in boundary mode

Amplitude voltage at the anode:

U a max = E amax o max =15.7 kV

Amplitude of the first harmonic of the anode current:

I a 1 max =2=69.2 A

Anode current pulse amplitude

I amm == 138.4 A

Equivalent anode load resistance:

The upper cutoff angle is determined from the equation

Where do we get = 0.31 rad = 18 0

DC component of the anode current taking into account the truncated pulse apex

Power consumed by the anode circuit

Power dissipated at the anode

Efficiency of the anode circuit in maximum mode

Excitation voltage amplitude in the control grid circuit and bias voltage

Auto bias resistance

where, = 71.2 0, ? 0.66

Grid current components

where are the coefficients and, taking into account the non-sinusoidal nature of the current pulse, assumed to be equal? 0.66, ? 0.75

Power consumption from previous PC stage and bias source

Power dissipated on the control grid

3 .2 Calculation of final cascade(OK) at the minimum point

The calculation of the minimum point mode is carried out according to the methods outlined in -. The minimum point mode is characterized by low voltages at the anode. In the region e a >0, the regime intensity increases and the MX is slightly bent. To mitigate these phenomena, automatic bias resistance R c .. is included in the current circuit.

The minimum mode parameters are calculated only for the control grid circuit, . The initial data for this calculation are U c max, E c 0, S, R c. .

To find the parameters of the grid current, using the method described in we find from the equation

Power consumption from the bias source and from the PC.

3 .3 Calculation of final cascade(OK) at the telephone point

Calculation of the telephone point mode is carried out according to the methods outlined in and.

Components of anode current

Anode voltage and load voltage amplitude

Power consumption and output

3.4 Final calculation cascade(OK) in modulation mode

Calculation of OC in modulation mode is carried out according to the method described in and.

Average power consumed by the anode circuit

Power delivered by the modulation device

Average power output from OK lamps

Average power dissipated at the anode.

Average power dissipated on the control grid

4 . Calculation of the pre-terminal cascade

The EP for the pre-final stage is selected according to the following rule: according to the reference tables given in the power amplification factor N p = 30 .. 50 is found. Let us take N p = 50. Then the power of the previous stage required to excite the OK is

For this power, a GU-39 B lamp is suitable, with P nom = 13 kW. Characteristics of GU 39 B are given in Appendix 2.

The P chain can be used as a coordination chain for QAP and OK.

5 . R Modulation device calculation

The MMU is implemented using a class D amplifier. The operating principle of this MMU is described in detail in and. A push-pull class D amplifier is designed to amplify the modulating signal. To supply the constant component I a 0t to OK, a separate power source with voltage E at and inductor L d 4 are used. The modulating voltage U Ш is supplied to the pulse-width modulator and the subsequent pulse amplifier and then to the lamp V 2. The second lamp V 1 is controlled by the voltage falling across the resistance R 1 from the anode current of the lamp V 2 .

The schematic diagram of this device is shown in Figure 5.1.

Figure 5.1 Schematic diagram of an MMU with a push-pull class D amplifier.

The advantages of this scheme include:

· a significant increase in the efficiency of the amplifier, due to the fact that the cascade lamps operate in the key mode, and the direct current component I a 0 t OK passes through the inductor with low winding resistance;

· constant efficiency of the amplifier at different levels of the amplified signal (with a rational choice of lamps, the efficiency in such an amplifier can reach 95% - 97%);

· absence of a heavy, bulky, expensive modulation transformer.

The disadvantages of this scheme include:

· the need to carefully adjust the control of the lamps to prevent their simultaneous opening, which would lead to a short circuit of the 2E a power source.

Diodes VD 1 and VD 2 are designed to prevent interruption of the current in the L d 2 coil when the lamps are switched.

Since the calculation of the OK mode parameters has been completed, it is determined

Based on the calculated parameters, the GU-66 B lamp is selected.

Diodes VD1 and VD2 are selected according to the following parameters:

Reverse voltage E rev E p,

Maximum pulse current I D max = 38 A

The forward resistance of the open diode r D is preferably as low as possible. The inductance rating of the filter choke L d 1 is selected in several Henrys. L d 1 = 5 Gn.

Capacitor C 1 is selected from the condition then C 1 = 253 pF

The filter Ld 2, Ld 3, C 2, C 3 is made in the form of a half-link L d 2 C 2 according to Butterworth. Hence

The coupling capacitor C 4 is selected from the condition

Then C 4 = 688 nF.

is chosen from the condition Then we can put

Resistance R 1 is selected so that the inequality is satisfied

where is the cutoff voltage of the anode current of lamps VL1 and VL2.

Thus R 1 = 150 Ohm.

The clock frequency f t is selected from the condition f t = (5..8) F c. Choose f t = 70 kHz.

6 . Ra output loop system account

The calculation of the output oscillatory system is carried out according to the method outlined in and.

The purpose of output oscillatory systems in radio transmitters is to perform the following functions:

· approval active resistance R A antenna feeder with the necessary for normal operation output stage with equivalent load resistance R e in the anode circuit;

· compensation reactance X A of the antenna or feeder so that the VCS operates on an active load and delivers the maximum power to the antenna;

· filtering of harmonics generated electronic devices in the output stages.

To select a video conferencing design, let’s calculate the required filtration

Based on the graph of the dependence s VKS (F required), the design of the output oscillatory system is determined. For z VKS =0.92 and Ф required =2.1 10 3 in the VKS design will look like (Figure 6.1):

Figure 6.1 Schematic diagram of the output oscillatory system.

Maximum and minimum feeder input impedance

Calculation of VKS elements is carried out according to the methodology outlined in.

Then for the first P-chain we have

For the second P chain

Then the ratings of the VKS elements should vary within

7 . Conclusion

As a result of the work done, a radio broadcast transmitter with amplitude modulation was designed in accordance with the technical specifications. The OK, modulation device and output loop system were calculated and the elements for constructing these devices were selected. The MMU is made according to a circuit with a push-pull class D amplifier, which helps to increase the efficiency of the amplifier and simplify its circuit. To match the active resistance of the antenna feeder with the equivalent load resistance in the anode circuit necessary for normal operation of the output stage, as well as to compensate for the reactance of the feeder and to filter harmonics generated by electronic devices in the output stages, an output circuit system with a double U-shaped circuit is used.

Annex 1

Characteristics of the generator triode GU 66 B

The GU-66B generator triode is designed to amplify power at frequencies up to 30 MHz in stationary transmitting radio devices, both in circuits with a common grid and in circuits with a common cathode.

General information

The cathode is thoriated carbided tungsten, directly heated. The design is metal-ceramic with ring leads of the cathode and grid. Cooling - forced: anode - water; legs - air. Height no more than 420 mm. Diameter no more than 211 mm. Weight no more than 23 kg.

Electrical parameters

Filament voltage, V

Filament current, A

Characteristic slope, mA/V

Gain (at anode voltage 4 kV, anode current 8 A)

Interelectrode capacitances, pF, no more

day off

checkpoint,

Highest filament voltage

Largest starting current filament, A

Maximum dissipation power, kW

Highest temperature of the leg and ceramic-metal junctions, °C

broadcast transmitter amplitude modulation transformer

Appendix 2

Characteristics of GU - 39 B

Permissible influencing factors during operation

Ambient temperature, C 0

Relative air humidity at temperatures up to 25 °C, %

Electrical parameters

Filament voltage, V

Filament current, A

Characteristic slope, mA/V

Output power kW, not less

Maximum permissible operating data

Highest anode voltage (constant), kV

Greatest operating frequency, MHz

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Transmitter exciters are quite complex devices. They may include frequency synthesizers, a unit for generating types of work, a transfer unit, and a buffer amplifier. In Fig. Figure 2.1 shows a generalized block diagram of the exciter, which includes all of the listed blocks.

The exciter's task is to generate a high-frequency signal in certain range frequencies, ensuring the required nature of frequency tuning over the operating range, the required stability of the oscillation frequency, the formation of various types of work. In practice, there is a wide variety of ways to construct a pathogen. The choice of method for constructing an exciter can be significantly influenced by the requirements for the speed of switching the operating frequency, the level of by-products in the spectrum of the output signal, and the types of work that are formed in the exciter.

Rice. 2.1. Exciter block diagram

The types of work that are formed in the exciter mean different kinds modulation (manipulation) of a high-frequency signal. There are quite a lot of them. First of all, these are angle modulation, single-sideband modulation, amplitude modulation and others. Some of them are main, others are auxiliary for certain types of radio transmitters. Modulation is carried out at fixed subcarrier frequencies in a special block included in the exciter, which is called the block for generating types of work (BFVR). High frequency signals generated on fixed subcarriers using special block, called a transfer unit (BT), is moved to the working frequency range.

The output device of the exciter is a buffer amplifier (BU). Distinctive feature Control units from other types of amplifiers have a high input impedance. The high input impedance of the control unit ensures decoupling of the exciter from the subsequent amplification path of the RF signal.

The main part of the exciter in modern transmitters is the frequency synthesizer. The frequency synthesizer generates a grid of highly stable frequencies. The frequency grid replaces the continuous operating frequency range with discrete frequencies in increments of F, which is called the grid spacing. The grid step can be from fractions of Hz to tens of MHz. In some VHF communication systems, the grid step is taken to be 25 kHz. This step allows you to organize independent communication channels at adjacent grid frequencies without mutual interference with each other (the principle of frequency division of channels).

Any grid frequency can be represented as

where is a coefficient that can be changed. The required grid frequency is set by a control command (CU) coming from an external device, which sets the required coefficient value.

In addition, the synthesizer can additionally generate one or more fixed subcarrier frequencies for the BFVR, on which modulation is carried out.

The operating frequency is generated at the output of the exciter transfer unit. In transmitters, a transfer unit is a mixer equipped with a bandpass filter. A mixer is a nonlinear device. When signals arrive at the inputs of the mixer with different frequencies and at its output a signal appears, the spectrum of which contains harmonics of the form

where and are arbitrary integers. The main combination frequencies are the frequencies when and: - when transferring a signal up and - when transferring a signal down. In transmitters, the first option is more often used, in receivers - the second option. The operating frequency of the transmitter is formed by summing the signal with the grid frequency and a signal with one of the fixed frequencies coming from the BFVR:

The transfer block's bandpass filter clears the output signal of harmonics and other combinational spectral components. The filtered signal is supplied to the input of the control unit and then to the input of the RF signal power amplifier.

Transmitters in relatively low-power communication systems most often use one type of modulation, such as angle modulation. In this case, the BFVR turns out to be quite simple. For its operation, only one additional subcarrier frequency is formed in the synthesizer. Just such a case is considered below. However, in general, the proposed method for developing an exciter is acceptable for any transmitters.


The development of an exciter consists of the selection and calculation of its individual components.

2.1. Frequency synthesizers

If the transmitter is designed to operate in a frequency range, and the required instability value of the operating frequency is at the level of quartz self-oscillators (AG), then it is most advisable to use a frequency synthesizer in the transmitter exciter.

Basic parameters of synthesizers

1. Operating frequency range of the synthesizer……………….. .

2. The total number of frequencies generated by the synthesizer is…………..

3. Number of additional fixed frequencies

The oscillation power at the synthesizer output is usually a fraction of a mW. Currently, the formation of a frequency grid in synthesizers is carried out by two main methods:

1. Direct synthesis method.

2. By the method of reverse (indirect) synthesis.

Direct synthesis method

The direct synthesis method is based on the formation of a frequency grid through the use of simple arithmetic operations - multiplication, division, summation, subtraction. Based on the type of element base used, synthesizers of the direct synthesis method can be analog, digital, or combined.

The technology of radio transmitting devices is developing continuously and intensively. This is due to the decisive role of transmitters; new and new ideas are being introduced, thanks to which the power consumption of devices is reduced, the quality of their operation and reliability are increased, with the use of chip technologies, the size and cost of radio systems for transmitting and retrieving information, radio control, etc. are reduced.

Almost the entire population of the Earth is served by radio transmitters of sound and television broadcasting. These are transmitters with power ranging from milliwatts to hundreds of kilowatts and units of megawatts. Image transmitters use amplitude modulation, and sound transmitters use frequency and phase modulation.

Essentially, radio communication is an electromagnetic oscillation propagating in space, carrying information. If the information is in the amplitude of an electromagnetic oscillation, then we talk about amplitude modulation (or AM); if it is in frequency or phase, then we talk about frequency (FM) or phase (PM) modulation.

Nowadays, radio stations are widely used, i.e. devices that combine both a radio receiver and a radio transmitter and are capable of both receiving and transmitting over a wide range of frequencies.

Radio communication is of great importance for modern man and is used by him in almost all areas of his activity, therefore, specialists in electronics and radio communications are very much needed.

In this case, it is necessary to select a block diagram and design the final and pre-terminal stages of a low frequency radio communication (LRC) transmitter with frequency modulation.

NRS transmitters are used in the HF and VHF bands to transmit messages to short distances. Transmitters of this type are designed to operate on one fixed frequency or over a range of frequencies.

The design (integration) of radio transmitting devices (RTD) on ICs is based on general principles design of microelectronic equipment, which acquire some features associated with the specifics of the transmitting equipment.

Distinctive features of the RPU are:

  • - analog nature of the signal, its large dynamic range(fractions of microvolts - units of volts);
  • - wide frequency range (from direct current- at the detector output, up to hundreds of megahertz or tens of gigahertz - at the output);
  • - big number irregular connections;
  • - functional diversity of nodes (blocks) with their relatively small total number.

Functional blocks (cascades) have varied requirements, often depending on the type of signals. In some components, manufacturing precision must be ensured. It often turns out to be necessary to change the parameters of elements in the process of adjusting the equipment, which is undesirable in microelectronic designs.

Digital ICs can be used to implement almost any signal processing algorithm carried out in receiving and amplifying devices, including elements of optimal radio reception.

Frequency modulation communication radios are designed to operate on a single fixed frequency or over a range of frequencies. In the first case, the operating frequency is stabilized by a quartz resonator, and to generate FM oscillations, both direct and indirect frequency control methods can be used. The block diagram of a transmitter using the direct FM method is shown in Fig. 1.

Fig.1.

The modulating voltage U is supplied to the varicap, with the help of which the quartz self-oscillator (KG) is modulated in frequency.

The quartz oscillator operates at frequencies of 10-15 MHz, then its frequency is multiplied n times to the operating value, the signal is fed to a power amplifier (PA) and through the CS communication circuit to the antenna.

The indirect FM method is based on converting phase modulation (PM) into frequency modulation by introducing an integrating element, i.e., a filter, into the circuit low frequencies(LPF). The block diagram of the transmitter using the indirect method of obtaining FM is shown in Fig. 2.


Fig.2.

A discrete frequency grid synthesizer is used as the exciter of the FM band transmitter, the slave oscillator of which is controlled by two varicaps (Fig. 3).


Fig.3.

The modulating voltage U is supplied to the varicap VD1, and the modulating voltage to the varicap VD2 control voltage phase-locked loop (PLL) systems. The separation of control functions is explained by the fact that the frequency deviation under the influence of the modulating signal is relatively small (3-5 kHz) in comparison with the tuning range of the slave oscillator (VCO) by the control signal from the output of the PLL system. Therefore, the varicap VD1 is connected to oscillatory circuit The VCO is significantly weaker than VD2. The frequency grid step at the transmitter output, depending on the operating range, can be 5; 10; 12.5; 25 kHz.

To increase stability, it is necessary that the powerful final amplifier influence the operation of the VCO as little as possible, so they are isolated in frequency by introducing a frequency multiplier into the structure of the transmitter. In this case, the synthesizer grid step is reduced by n times, where n is the multiplier frequency multiplier.


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