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1

Andrew CLEGGU.S. National Science Foundation

aclegg@nsf.gov

Third Summer School on Spectrum Management for Radio AstronomyTokyo, Japan – June 3, 2010

Digital TV and Its Impact onRadio Astronomy

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nAnalog Television Terrestrial

Broadcasting Standards

2

Abbrev Name Main Geographic Use

PAL Phase Alternating Line Most of Europe, Australia, Parts of Asia (including India & China), Most of Africa, Eastern South America

NTSC National Television System Committee

North & Central America, Western South America, Japan, Philippines, Thailand, Taiwan, South Korea

SECAM Sequential Color with Memory

France, Russia & former Soviet republics, portions of Africa, Madagascar

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nAnalog TV Standards Worldwide

3

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nDigital Television Worldwide

• Worldwide, terrestrial TV broadcasts are switching from analog to digital modulation> Different countries have different schedules for

switching over (most by 2015)> Some satellite TV broadcasting has been digital for

more than 15 years

• Japan is deploying ISDB-T technology, replacing NTSC and analog HDTV MUSE standards> ISDB-T also being widely deployed in South America

• North America is deploying ATSC digital TV to replace NTSC analog standard> U.S. digital transition is completed for “full-service”

broadcasts; legacy NTSC remains for low-power stations

• Australia and Europe are deploying DVB-T

• China is rolling its own (DMB-T)4

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n Digital TV Terrestrial Broadcasting Standards

5

Abbrev NameOver-the-Air Modulation Type

Main Geographic Use

DVB-T Digital Video Broadcasting – Terrestrial

Coded Orthogonal Frequency Division Multiplexing (COFDM) (QPSK, 16QAM, and 64QAM)

Europe, Russia, Australia, Parts of Asia

ISDB-T Integrated Services Digital Broadcasting - Terrestrial

Coded Orthogonal Frequency Division Multiplexing (COFDM) (DQPSK, QPSK, 16QAM, and 64QAM)

Japan, South America (ISDB-T International)

ATSC Advanced Television Systems Committee

8-level Vestigial Sideband (8VSB)

North America, South Korea

DMB-T/H Digital Multimedia Broadcast – Terrestrial/Handheld

Time Domain Synchronous Orthogonal Frequency Division Multiplexing (TDS-OFDM)

China only

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nDigital TV Standards Worldwide

6

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nDigital Transition Worldwide

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Completed, no analog / Completed for full-service stations / In transition /Planned / No transition planned / No Information

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n TV Spectra

8

DVB-T (OFDM)

ISDB-T (Yellow) (OFDM)

DigitalAnalog

PAL / SECAM / NTSC Generic(All have video, chrominance, and audio

carriers. Some differences in total bandwidth and frequency offset between carriers.)

ATSC(8-VSB)

PAL

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Maximum Transmit Power (U.S.)

9

Chan Freq (MHz)Maximum Analog

EIRP (kW)Maximum Digital

EIRP (kW)

2 – 6 54 – 72 & 76 – 88 164 74

7 – 13 174 – 216 518 262

14 – 51 470 – 698 8222 1640

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nDTV Unwanted Emissions Limits (U.S.)

(Assumes full-power 1640 kW EIRP)

10

Fig. 1.14.5: Unwanted Emissions Limits for a Full-Power (1640 kW EIRP)Digital TV Signal

-110

-100

-90

-80

-70

-60

-50

-40

0 1 2 3 4 5 6 7 8 9 10

Frequency Offset from Channel Edge (MHz)

EIR

P L

imit

fo

r U

nw

an

ted

Em

issi

on

s

[dB

(W/H

z)]

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n Comparison of Analog (NTSC) and Digital (ATSC) TV Signal Spectra

11

Direct comparison of digital (8-VSB modulation, left) and analog (AM-VSB, PM, and FM, right) TV signals, of the same station from the same tower at the same time. The analog signal has more power because of the large video carrier, but the digital signal fills in the spectrum completely.

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n Comparison of Digital (ATSC) and Analog (NTSC) Signals

12

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n Ratio of Power Spectral Density of Digital (ATSC) to Analog (NTSC)

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n Ratio of Power Spectral Density of Digital to Analog (detail)

14

Detail of DTV/Analog TV

0

1

2

3

4

5

6

7

8

9

10

0.000 1.000 2.000 3.000 4.000 5.000 6.000

Frequency Offset from Bottom of Channel (MHz)

(DTV

PSD

)/(An

alog

TV

PSD)

For equivalent digital and analog TV signals, the digital

power spectral density exceeds the analog PSD over 94% of the bandwidth, and by

as much as 3 orders of magnitude.

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nHow to Identify TV Signal

Technology Bandwidth Most dominant spectral characteristic Secondary spectral characteristic Other spectral characteristic(s)

NTSC (analog; System M) 6 MHz

Strong video carrier peaked at 1.25 MHz above bottom channel edge. When tuned in AM mode on an appropriate receiver, sounds like a buzzing sound that changes with changes in the TV picture.

FM audio carrier 5.75 MHz above bottom edge of channel (250 kHz below top edge). Audio can be clearly monitored in wideband FM mode with appropriate radio receiver.

Chrominance carrier (phase and amplitude modulated) 4.829545 MHz above bottom of channel.

PAL (analog; Southern Africa; System I) 8 MHz

Strong video carrier peaked at 1.25 MHz above bottom channel edge. When tuned in AM mode on an appropriate receiver, sounds like a buzzing sound that changes with changes in the TV picture.

FM audio carrier 7.2496 MHz above bottom edge of channel (250 kHz below top edge). Audio can be clearly monitored in wideband FM mode with appropriate radio receiver.

Chrominance carrier 5.68361875 MHz above bottom-edge of channel.

PAL (analog; Australia; System B) 7 MHz

Strong video carrier peaked at 1.25 MHz above bottom channel edge. When tuned in AM mode on an appropriate receiver, sounds like a buzzing sound that changes with changes in the TV picture.

FM audio carrier 6.75 MHz above bottom edge of channel (250 kHz below top edge). Audio can be clearly monitored in wideband FM mode with appropriate radio receiver.

Chrominance carrier 5.68361875 MHz above bottom-edge of channel.

ATSC (digital) 6 MHz

Flat spectrum except very narrow pilot tone carrier approximately 309.4 kHz above bottom edge of channel. Pilot tone can be heard in CW mode of an appropriate radio receiver, otherwise rest of signal just sounds like gaussian noise.

ISDB-T, DVB-T (digital) 6, 7, & 8 MHzFlat spectrum, OFDM. No significant spectral features. Identified by frequency and bandwidth.

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Digital and Analog TV in Mitaka

Japanese NTSC TV broadcast on channel 3 (102 – 108 MHz).

Video carrier (103.25 MHz)

Color carrier(106.78 MHz)

Audio carrier(107.75 MHz)

Japanese ISDB-T broadcasts on channels 25, 26, & 27 (542 – 560 MHz)

Channel 26(548 – 554 MHz)

Channel 25(542 – 548 MHz) Channel 27

(554 – 560 MHz)

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n Observational Comparison ofDigital and Analog TV Interference

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nTelevision Interference Caused by Anomalous

Propagation at the Murchison Widefield Array Site

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Digital TV signal in Australian channel 7 (181 – 188 MHz), and narrowband interference from analog (PAL) luminance, chrominance, and audio carriers of channels 6 (174 – 181 MHz),

8 (188 – 195 MHz), and (partially) 9 (195-202 MHz). The digital TV signal is believed to be arising from a distance of 290 km during a period of anomalous propagation. Data obtained in March 2010.

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nTV Broadcasts and Rec. 769

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Digital TV and Redshifted HI

Fig. 1.14.2: U.S. Television Channels After Feb 17, 2009 Digital TV TransitionV

HF

UH

F

MHzz(HI)

5425.3

2

6022.7

3

6620.5

4

7218.7

7617.7

5

8216.3

6

8815.1

~

1747.2

7

1806.9

8

1866.6

9

1926.4

10

1986.2

11

2046.0

12

2105.8

13

2165.6

MHzz(HI)

4702.02

14

4761.98

15

4821.95

16

4881.91

17

4941.88

18

5001.84

19

5061.81

20

5121.77

21

5181.74

22

5241.71

23

5301.68

24

5361.65

25

5421.62

26

5481.59

27

5541.56

MHzz(HI)

5541.56

28

5601.54

29

5661.51

30

5721.48

31

5781.46

32

5841.43

33

5901.41

34

5961.38

35

6021.36

36

6081.34

6141.31

38

6201.29

39

6261.27

40

6321.25

41

6381.23

MHzz(HI)

6381.23

42

6441.21

43

6501.19

44

6561.17

45

6621.15

46

6681.13

47

6741.11

48

6801.09

49

6861.07

50

6921.05

51

6981.03

52

7041.02

53

7101.00

54

7160.98

55

7220.97

MHzz(HI)

7220.97

56

7280.95

57

7340.94

58

7400.92

59

7460.90

60

7520.89

61

7580.87

62

7640.86

63

7700.84

64

7760.83

65

7820.82

66

7880.80

67

7940.79

68

8000.78

69

8060.76

Allocated to radio astronomy. Not used for TV.

Used for land mobile instead of TV in some major cities.Reallocated to mobile and f ixed use.

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n Worldwide Lower VHF Channel Plans

21Figure from Wikipedia, based on data from “World Analogue Television Standards and Waveforms” (http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html)

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n Worldwide Upper VHF Channel Plans

22Figure from Wikipedia, based on data from “World Analogue Television Standards and Waveforms” (http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html)

See color key onprevious slide

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n Comparison of Analog and DTV Channel Allotments

23

• Allotments specify which channels are available for use in each city or market area> Allotments are based on market size, co- and adjacent-

channel interference criteria, geography, frequency, and other considerations

• Given the lucrative nature of a TV license, virtually all allotted channels are spoken for

• There are significant differences between the DTV allotments after the transition and the analog allotments prior to the transition

• A comparison of the allotment tables provides a quick snapshot of the imminent changes in the spectrum landscape.

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Number of Analog TV Allotments Per Channel Prior to DTV Transition

58

61

64

5658

6161

565757

58

68

3030

27272726

28

3230

3334

26

31

27

22

25

22

1817

25

2122

24

0

20

17

22

141616

1918

19

1615

21

1818

1312

16

10

1312

13

79

1012

79

6

119

13

6

0

10

20

30

40

50

60

70

80

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68

TV Channel

Nu

mb

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nal

og

TV

Sta

tio

n A

llo

tmen

ts

Σ = 1756

Analog TV AllotmentsBefore DTV Transition

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Digital TV AllotmentsAfter DTV Transition

Number of Digital TV Allotments Per Channel After DTV Transition

7 7

2

13

8

68

6361

68

5757

76

24

40

3436

37

48

3940

414141

31

4140

38

35

32

36

41

33

42

33

44

0

343435

29

3537

39

3331

3031

32

27

30

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00

10

20

30

40

50

60

70

80

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68

TV Channel

Nu

mb

er o

f D

igit

al T

V S

tati

on

All

otm

ents

Σ = 1811

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Difference between Digital and Analog TV Allotments

Change in TV Allotments Per Channel After DTV Transition

-200%

-150%

-100%

-50%

0%

50%

100%

150%

200%

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68

% C

han

ge

( ND

TV -

NA

nal

og)/N

An

alo

g

Lower VHF, Chs 2 - 6 (54 - 72 & 76 - 88 MHz)

Upper VHF, Chs 7 - 13(174 - 216 MHz)

UHF Chs 14 - 51 (470 ~ 698 MHz)

No longer used, Chs 52 - 69 (698 - 806 MHz)

Ch 37 (608 - 614 MHz)(not used for TV)

ΔN = +55

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n Summary• The world is switching to digital terrestrial TV

broadcasting

• Digital TV produces more apparent interference than analog TV

• Both digital TV and (in some countries) the refarming of TV broadcast spectrum will make observations using TV band frequencies more challenging

• TV interference is most disruptive to the search for highly redshifted HI, such as the search for the Epoch of Reionization (EOR)

• TV interference in general, and digital TV interference in particular, have been shown to impact radio observatories hundreds of km from the transmitting source

• Radio astronomers can generally not expect any regulatory protections when using TV spectrum for observing

• Future instruments such as the SKA must take TV interference into account 27