This document discusses various broadcasting and video systems. It covers AM broadcasting which uses frequency bands and carrier spacing to avoid signal overlap. It also discusses FM broadcasting which uses frequency division multiplexing to transmit stereo sound. The document also covers black and white television which uses raster scanning to transmit video as a serial data stream, and color television techniques like PAL and NTSC which encode color images and multiplex color signals for transmission.

1. BROADCASTING AND VIDEO
SYSTEMS

2. AM Broadcasting

3. AM Broadcasting
 International agreements design specific frequency
bands for specific uses
 They also specified the carrier spacing, so that
transmitted sidebands will not overlap
 Carrier spacing ~ 9 kHz. Therefore each modulated
transmission is confined to its allocated channel. So
the receiver can select the desired transmission and
reject the others

4. AM Broadcasting

5. AM Broadcasting (Receiver side)

6. AM Broadcasting
 Filters are used at the receiver to select the desired
channel
 Ideally, filters allow only the desired channel to pass
through, and blocks all other channels

7. AM Broadcasting

8. Short Wave Broadcasting
 Short wave – is a RF spectrum, between about 3 to 30
MHz – able to transmit radio signals as they reflect off
the ionosphere
 Because of this, short wave can be used for long
distances, unlike AM and FM radio frequencies
 Applications
 Communications during disasters, to provide emergency information
and relief
 Long distance education
 Popularity of short wave is diminishing as broadcasters
today use satellites and cable TV for broadcasting

9. FM Broadcasting
 Advantage of FM broadcasting compared to AM is
the availability of stereo sound
 FM stereo involves the transmission and reception of
two related audio signals, ‘Left’ (L) and ‘Right’ (R)
 Frequency Division Multiplexing (FDM) is used to
combine the L and R signals, to produce ‘sum’ and
‘difference’ signals
 ‘Sum’ and ‘difference’ signals are transmitted
L  R
Sum = Difference =
2
L  R
2

10. FM Broadcasting

11. FM Broadcasting
 At the receiver, L and R are recovered:
L = sum + difference
R = sum - difference
 The 19 kHz pilot tone is used for demodulation
purpose

12. Black and White TV

13. Black and White TV
 Black and white TV displays information about two-dimensional
pattern of brightness
 At transmitter, raster scanning is used to convert
a series of still pictures (video is a series of still
pictures) into a single serial data stream
 In raster scanning, a light sensor scans the picture,
detecting the variation of brightness along each line
of the picture
 Arrangement of lines and the order/speed/direction
in which they’re scanned is called the raster
pattern

14. Black and White TV
 At the receiver, an electron beam is scanned across a
screen which is covered with a phosphor
 Raster patterns at transmitter (in video camera)
and TV receiver must be the same and correctly
synchronized

15. Interlaced Scanning
Interlaced scanning raster
“Interlaced” scanning – odd-numbered lines are traced first, then the
even-numbered lines – results in “odd” and “even” fields

16. Interlaced Scan

17. Colour TV Technique
 To get colour pictures, we have to transmit three pictures
– one red, one blue and one green. These are overlaid
by TV to produce a colour image

18. Colour TV Technique
 How to multiplex (combine for transmission) these
colour information?
Two systems:
Phase Alternating Line (PAL)
National Television System for Colour (NTSC)

19. PAL
 Used in UK
 Colour in RGB format is converted to YUV format,
where
 Y represents luminance (brightness)
 U and V represent chrominance (colour components)
 625 scan lines per frame
 25 frames per second
 Interlaced

20. NTSC
 Used in North America
 Colour in RGB format is converted to YIQ format,
where
 Y represents luminance (brightness)
 I and Q represent chrominance (colour components)
 525 scan lines per frame
 30 frames per second
 Interlaced

21. Types of Colour Video Signals
 1) Component video
 Transmits 3 signals = 1 luminance + 2 chrominance
 Highest bandwidth requirement
 Best colour quality
 2) Composite video
 Transmits 1 line only: Both luminance and chrominance are
mixed into a single carrier signal – may cause interference
between luminance and chrominance
 Lowest bandwidth requirement
 Lowest picture quality

22. Types of Colour Video Signals
 3) Separated video (S-video)
 Transmits two signals = 1 luminance + 1 for composite
chrominance
 Medium bandwidth requirement
 Good picture quality (better than composite video, but not as
good as component video)