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1. Television broadcasting networks. Frequency channels. TV signal transmission

Lecture



1.1. Frequency channels of television and VHF FM broadcasting.

The descriptions of various types of antennas and other antenna-feeder devices, as well as the related consideration of theoretical issues, are carried out using the classification of oscillations by wavelength (Table 1.1) in accordance with the Radio Regulations adopted by the International Radio Advisory Committee (CCIR).

Table 1.1. Radio spectrum frequency bands

nom

Frequency range (excluding the lower limit, including the upper limit)

Letter designation

lanes

Metric name in accordance with the Radio Regulations

The name of the radio waves used in the literature

four

3 - 30 kHz

VLF (VLF)

Miriametrovye

Extra Long (ADL)

five

30 - 300 kHz

LF (LF)

Kilometers

Long (DV)

6

0.3 - 3 MHz

SC (MF)

Hectometric

Medium (SV)

7

3 - 30 MHz

HF (HF)

Decameter

Short (KB)

eight

30 - 300 MHz

VHF (VHF)

Meters

Ultrashort (VHF)

9

0.3 - 3 GHz

UHF (UHF)

Decimeter

Ultrashort (VHF)

ten

3-30GHz

Microwave (SHF)

Centimeter

Ultrashort (VHF)

eleven

30 - 300 GHz

EHF (EHF)

Millimeter

Ultrashort (VHF)

12

300-3000 GHz

Ghv

Decimillimeter

Ultrashort (VHF)

For VHF FM broadcasting and television, the eighth meter band and the ninth band of decimeter waves are used. The whole range of frequencies allocated for TV broadcasting and VHF FM broadcasting is divided into bands designated by Roman numerals I - V (Table 1. 2). For terrestrial TV broadcasting, the development of the tenth and eleventh bands is provided - VI range (12 GHz, 40, 5 ... 42, 5 GHz and 84 ... 86 GHz). Bandwidth of one TV channel

(according to the standard MORT) 8 MHz, the separation between the carrier frequencies of the image and sound signals is 6. 5 MHz.

Table 1. 2. Radio wave bands and frequency bands

Broadcast Frequency Range

Channel TV number

lср

channel, m

fср

channel, MHz

Frequency band

Carrier frequency

channel, MHz

Images,

MHz

sound, MHz

METRO

WAVES

VHF

(Vhf)

I

one

5.72

52.5

48.5-56.5

49.75

56.25

I

2

4.84

62

58-66

59.25

65.75

VHF FM RADIO

66-73

Standard MORT (Eastern Europe)

87, 5-108

ICRC Standard (Western Europe)

METRO

VHF WAVES (VHF)

II

3

3.75

80

76-84

77.25

83.75

II

four

3.41

88

84-92

85.25

91.75

II

five

3.13

96

92-100

93.25

99.75

1-CABLE

STRIP

(SK-1 ... 8

or S-1 ... 8)

S-1

114

110-118

111.25

117.75

S-2

122

118-126

119.25

125.75

S-3

130

126-134

127.25

133.75

S-4

138

134-142

135.25

141.75

S-5

146

142-150

143.25

149.75

S-6

154

150-158

151.25

157.75

S-7

162

158-166

159.25

165.75

S-8

170

166-174

167.25

173.75

METRO

WAVES

VHF

(Vhf)

III

6

1.69

178

174-182

175.25

181.75

III

7

1.61

186

182-190

183.25

189.75

III

eight

1.55

194

190-198

191.25

197.75

III

9

1.49

202

198-206

199.25

205.75

III

ten

1.43

210

206-214

207.25

213.75

III

eleven

1.38

218

214-222

215.25

221.75

III

12

1.33

226

222 - 230

223.25

229.75

2-CABLE

(CK-11. 18

or S-11 ... 19)

S11

230 - 238

231.25

237.75

S12

238 - 246

239.25

245.75

S13

246 - 254

247.25

253.75

S14

254 - 262

255.25

261.75

S15

262 - 270

263.25

269.75

Continued table. 1.2.

Broadcast Frequency Range

Channel TV number

lср channel. m

fср

channel, MHz

Channel bandwidth, MHz

Carrier frequency

images, MHz

sound. MHz

2-CABLE

STRIP

(SK-11 .. 18

or S-11 ... 19)

S16

270-278

271.25

277.75

S17

278-286

279.25

285.75

S18

286-294

287.25

293.75

S19

294-302

295.25

301.75

3-CABLE

Strip

range

Super

bond

S20

302-310

303.25

309.75

S21

310-318

311.25

317.75

S22

318-326

319.25

325.75

S23

326 -334

327.25

333.75

S24

334 - 342

335.25

341.75

S25

342-350

343.25

349.75

S26

350 -358

351.25

357.75

S27

358-366

359.25

365.75

S28

366-374

367.25

373.75

S29

374 - 382

375.25

381.75

S30

382 - 390

383.25

389.75

S31

390-398

391.25

397.75

S32

398-406

399.25

405.75

S33

406-414

407.25

413.75

S34

414-422

415.25

421.75

S35

422-430

423.25

429.75

S36

430-438

431.25

437.75

S37

438 -446

439.25

445.75

S38

446-454

447.25

453.75

S39

454-462

455.25

461.75

S40

462-470

463.25

469.75

Decimeter

waves

VHF

(U H F)

IV

21

0.632

474

470-478

471.25

477.75

IV

22

0.622

482

478-486

479.25

485.75

IV

23

0.612

490

486-494

487.25

493.75

IV

24

0.602

498

494 - 502

495.25

501.75

IV

25

0.592

506

502 - 510

503.25

509.75

IV

26

0.583

514

510-518

511.25

517.75

IV

27

0.574

522

518-526

519.25

525.75

IV

28

0.566

530

526 - 534

527.25

533.75

IV

29

0.557

538

534 - 542

535.25

541.75

IV

thirty

0.549

546

542-550

543.25

549.75

IV

31

0.541

554

550 -558

551.25

557.75

IV

32

0.533

562

558- 566

559.25

565.75

IV

33

0.526

570

566 -574

567.25

573.75

IV

34

0.519

578

574 -582

575.25

581.75

Continued table. 1.2.

Broadcast Frequency Range

Channel TV number

lср

kana-la.m

fср

channel. MHz

Strip

Carrier frequency

channel, MHz

images, MHz

sound, MHz

DZIMETROVYE WAVES

OB H (UHF)

V

35

0.512

586

582-590

583.25

589.75

V

36

0,505

594

590 -598

591.25

597.75

V

37

0.498

602

598 - 606

599.25

605.75

V

38

0,491

610

606-614

607.25

613.75

V

39

0.485

618

614-622

615.25

621.75

V

40

0.479

626

622-630

623.25

629.75

V

41

0.473

634

630-638

631.25

637.75

V

42

0.467

642

638-646

639.25

645.75

V

43

0.461

650

646- 654

647.25

653.75

V

44

0.456

658

654 - 662

655.25

661.75

V

45

0.450

667

662-670

663.25

669.75

V

46

0.445

674

670-678

671.25

677.75

V

47

0.440

682

678-686

679.25

685.75

V

48

0.435

690

686-694

687.25

693.75

V

49

0.430

698

694 - 702

695.25

701.75

V

50

0.425

706

702-710

703.25

709.75

V

51

0.420

714

710-718

711.25

717.75

V

52

0.415

722

718 - 726

719.25

725.75

V

53

0.411

730

726-734

727.25

733.75

V

54

0.406

738

734- 742

735.25

741.75

V

55

0.402

746

742-750

743.25

749.75

V

56

0.398

754

750-758

751.25

757.75

V

57

0.393

762

758-766

759.25

765.75

V

58

0.389

770

766-774

767.25

773.75

V

59

0.385

778

774-782

775.25

781.75

V

60

0.381

786

782-790

783.25

789.75

V

61

0.378

794

790-798

791.25

797.75

V

62

0.374

802

798-806

799.25

806.75

V

63

0.370

810

806-814

807.25

813.75

V

64

0.367

818

814-822

815.25

821.75

V

65

0.363

826

822-830

823.25

829.75

V

66

0,359

834

830-838

831.25

837.75

V

67

0.356

842

838-846

839.25

845.75

V

68

0.353

850

846-854

847.25

853.75

V

69

0.349

858

854-862

855.25

861.75

V

70

0.346

866

862 - 870

863.25

869.75

V

71

0.343

874

870-878

871.25

877.75

V

72

0.340

882

878-886

879.25

885.75

V

73

0.337

890

886 - 894

887.25

893.75

V

74

0.334

898

894 - 902

895.25

901.75

V

75

0.331

906

902-910

903.25

909.75

Continued table. 1.2.

Broadcast Frequency Range

Channel TV number

lср channel, m

channel channel, MHz

Channel bandwidth, MHz

Carrier frequency

images, MHz

sound, MHz

Decimeter

waves

OB H (UHF)

V

76

0.328

914

910-918

911.25

917.75

V

77

0.325

922

918-926

919.25

925.75

V

78

0.322

930

926 - 934

927.25

933.75

V

79

0.379

938

934-942

935.25

941.75

V

80

0.317

946

942 - 950

943.25

949.75

1. 2. Transmission of television signals

The transmission of television signals is conducted at strictly fixed frequencies allocated on the basis of the grid of frequency channels for a given installation site of the transmitting station. The grid of frequencies for a given installation site of television transmission centers is constructed in such a way as to cover the maximum broadcasting territory and exclude mutual interference of reception from telecentres operating on adjacent channels. Therefore, the distance between the transmitting television stations operating on the same TV channels, to avoid mutual interference, is approximately 300-400 km.

In addition, each country plans transmission networks on the basis of its economic capabilities, with the result that separate frequency incompatibilities appear.

When planning a television network using data [1. 1], determining the service area of ​​television broadcasting (at the corresponding gain values ​​of the receiving television antennas). For satisfactory quality of the received image it is necessary to use antennas, the gain of which is indicated in Table. 1. 3. Here, E is the minimum value of the intensity of the radiation field of a radio signal of an image at a height of 10 m from the surface of the Earth, taken in decibels relative to 1 µV / m.

In television broadcasting, two types of wave polarization are used - horizontal and vertical. The use of vertical wave polarization in television broadcasting allows reducing the protection ratios for stations and repeaters operating on co-located and adjacent channels, which makes it possible to additionally use TV channels or reduce mutual interference from closely located telecentres. The use of different polarization allows reducing the allowable distances between them on the I, II range of broadcasting by 20%, and on the III range - up to 25% ... 30%.

Table 1. 3. Minimum values ​​of the intensity of the radiation field of a radio signal

frequency range

transmission frequency, MHz

E, mV / m

E, DB

antenna gain

Db

|

48, 5-66

316

50

four

II

76-100

501

54

4, 5

III

174-230

708

57

eight

IV

470-582

3162

70

ten

V

582-790 (958)

5000

74

15-18

1. 2. 1. Transmitting stations and repeaters

Television stations are divided into program and transmission. Software TV stations are television centers whose equipment ensures the reception of television broadcast signals with their subsequent transmission over a television transmission network. Transmitting television stations provide programs created in television centers.

According to the power of the image signal at the output of the television transmitter, the stations are conventionally subdivided into powerful (or high power) - more than 1 kW and low power - less than 1 kW. The transmission distance of programs by television centers slightly exceeds the line-of-sight distance between transmitting and receiving antennas, therefore transmitting stations are placed at a distance of 70 .. L 20 km.

In order to cover as wide a territory as possible with television broadcasting, television transmitting antennas are installed on high supports using natural terrain heights. Antenna support is a high-rise structure, which by design is divided into towers (H = 150 ... 550 m) and masts (H = 200 ... 350 m).

Panel, turnstile and antennas with radial and corner vibrators are used as transmitters.

The basic requirements that transmitting antennas must meet are the indiscriminate radiation of radio signals and the creation of the most uniform intensity. electromagnetic field in the service area.

The most important parameters of transmitting television antennas include:

- gain or directional gain;

- the shape of the radiation pattern (directivity) in the horizontal and vertical planes;

- polarization of radiated waves, etc.

To create the maximum field strength in the zone, the radiation power is increased, but at low elevation heights of the antenna, the field strength in the near zone may exceed the permissible sanitary norms.

The gain of transmitting antennas (relative to an isotropic radiator) in the 1-11 ranges is 6 ... 10, in the III range - up to 25, and for UHF ranges of the IV-V - up to 50.

For antennas with a high gain in the radiation pattern in the vertical plane, the number of side lobes increases, which is why at close distances from the transmitting station there appear areas with insufficient field strength for normal reception of television programs.

Of importance is the constancy of the input impedance of the antenna within the transmission band, determined by the TRAVELING WAVE RATIO (IPM) in the feed feeder. Transmitting antennas should provide an IPA of about 0, 9 in the transmission band.

To extend the service area and increase the level of the television signal in areas where there is an uncertain reception from the main television stations, a television repeater is used. Being a type of television stations, a television repeater is designed to receive and transmit programs of remote television centers with the possibility of changing the direction of radiation. Repeaters are divided into active and passive.

Passive repeaters allow you to change the direction of propagation of the television signal. However, they significantly weaken the field strength, so they can be used only with a sufficient signal level at the installation site (Fig. & 1. 1). Passive repeaters can be made in the form of reflective planes (metal mirror) or phased arrays. In the first case, these are flat single-line wire grids with a sufficiently high reflection coefficient, with cells of 0.1l in size (l is the average wavelength of re-emitted waves), and a turning device is provided for changing its position. Such repeaters can operate in a wide frequency range and re-emit the received energy of several channels simultaneously. In the second case, these are antennas, for example, of the "wave channel" type, forming two grids connected to each other. The signal energy received by one grid is emitted by another identical grid in the desired direction. The working frequency range is determined by the antennas used in it. To obtain good reception quality from a passive repeater, a direct signal at the reception site must be sufficiently weak and not create noticeable repetitions on the image.

  1. Television broadcasting networks.  Frequency channels.  TV signal transmission

Fig. 1. 1. Use of passive repeater

There is a large number of active repeaters in operation, of various purposes and operating parameters, intended for use in all television bands and having output power from 0, 1 W to 1 kW. Their main varieties are repeater-amplifier, repeater-transducer and repeater-transmitter. The television signal goes to the repeater as well as to the powerful transmitting stations - via radio relay lines, high-frequency cables, satellite communication systems, or directly over the air. The type of transmitting antennas is chosen taking into account the location of the service area and the installation site of the repeater. If the transponder is installed in the center of a populated area, then a transmitting antenna with a circular radiation pattern in the horizontal plane is applied, uniformly radiating power in all directions. Transmitting antennas with directional radiation are usually installed on repeaters located on the outskirts or outside settlements. The range of repeaters is limited by their output power, Pout (see table. 1. 4).

Table 1. 4. The range of the repeaters.

Pout

W

Range, km

VHF

UHF

one

5 ... 6

2 ... 3

ten

10 ... 12

4 ... 5

100

20 ... 30

8 ... 10


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Television and antennas. Theory. Broadcast and cable. Digital and analog

Terms: Television and antennas. Theory. Broadcast and cable. Digital and analog