Broadcast Basics

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Broadcast Basics

• Week 13

ICS 620
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BROADCAST BASICS
ICS 620 Week 13
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Introduction

• Video Basics (Analog Systems)
• Transmission Systems
• Wireless (terrestrial)
• Wired (cable television)
• Digital Video (Two Weeks)

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Video Standards

• Standards and Principals
• Persistence of Vision
• The rapid presentation of frames of video
  information to give you the illusion of smooth
  motion.

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Frequency StandardsFrame Frequency

• 16 Frames per Second (fps) Black and White
• 24 fps SOF
• Continuity of Action
• Problem of Flicker
• The gross alteration of light and dark

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Frequency StandardsField Frequency

• Frame Frequency x 2
• Continuity of Illumination

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Film Vs. Video

• Film - Project a complete picture
• Video - Scan, line by line, at a high rate of
  speed - 6 million bits per second

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How do we describe a picture?

• A picture element (pel or pixel) one at a
  time
  
• For each pel we need to somehow describe
• Brightness (luminance)
• Hue (phase, tint)
• Saturation (color intensity, chroma)

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Vertical Resolution

• The picture quality associated with the number of
  dots (pixels) used to construct the picture.
  
• 367,000 dots
• on 525 rows (vertical)

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Film vs. NTSC Specs

• Aspect Ratio

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Camera Tubes
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Early Camera Tubes
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Image Orthicon
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Electronic Scan (Camera Pickup Tube)
Target
Lens
Object
Electron Beam
Video Signal
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Scanning

• Progressive
• Interlace/Offset
• Interlace Example
• NTSC 525 lines, 30 frames/sec,
• 60 fields/sec

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Picture Tube
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Picture Tube
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Picture Tube
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Scanning a Focused Image
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Progressive Scanning
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Interlace Scanning
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Sync Pulses
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Differences Between Horizontal and Vertical Synch
Pulses

• Rate Duration
• Vertical 59.94/sec 13
• Horizontal 15,734.264/sec 31

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Waveform Sketch of a Video Signal
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A simple video waveform
One Line
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Waveform of Sync Pulses
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IRE Measurement Scale
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Vertical Blanking Interval (VBI)

• Lines 1-21 of each field
• Vertical Interval Test Signal (VITS)
• Vertical Interval Reference Signal (VIRS)
• Lines 1-9 V-sync and Equalizing Pulses
• Lines 12-14 SMPTE Time Code
• Lines 17-19 VITS and VIRS
• Line 20 Network Source Code (field 1)
• Line 21 Closed captioning (field 1)

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Kell Factor

• The Ratio of effective resolution to the
  theoretical resolution is known as the Kell
  Factor.
  

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Vertical Resolution Summary

• Max Lines/Frame 525
• Lost for Vertical Blanking 42 (21 lines per
  field)
  
• Visible 525-42 483
• Kell Factor 72.5
• Effective Resolution 350 lines

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Horizontal Resolution Summary

• (4.2 MHz Video Bandwidth)
• 4.2 cycles per microsecond
• x 52 microseconds (active scan)
• x 2 pixels per cycle
• 436 pixels per line

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Television Transmission

• Picture Information
• Blanking pulses
• Sync pulses
• Audio information

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What about Color?
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Component Nature of Color
R
G
B
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Video Color Palette
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Color Television

• R Red
• G Green
• B Blue
• B G Cyan
• G R Yellow
• B R Magenta

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NTSC Color Bars
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Block Diagram of Color Camera
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Gamma G

• A measurement of contrast, gamma correction is
  required because the brightness output of a
  camera does not correspond to the brightness
  recognition of the human eye.

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Composite Color

• Y Luminance Signal
• Y 30 red 59 green 11 blue
• C Chrominance Signal
• C I Q Matrix

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Color Matrix

• Saturation Amplitude of the I and Q signals
• Hue Phase developed by the difference in
  amplitude between the I and Q signals

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Transmitter Tube
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Color TV Transmitter
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TV Frequency Allocations
2 - 4 VHF-Lo 54 MHz - 72 MHz
5 - 6 VHF-Lo 76 MHz - 88 MHz
7 13 VHF-Hi 174 MHz 216 MHz
14 59 UHF 470 MHz 746 MHz
NOTE Natural breaks occur between channels 4 a
nd 5 channels 6 and 7 and channels 13 and 14.
Each channel is 6 MHz wide.
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NTSC Bandpass Characteristics (Black and White)
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Color TV Signal
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NTSC Bandpass Characteristics (Color)
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Color TV Signal
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Worldwide Standards

• National Television System Committee - NTSC
  (1953)
  
• Phase Alternation Line -PAL (1967)
• Sequentiel Couleur Avec Memoire - SECAM (1967)

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World TV Standards
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World TV Standards
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Principal TV Systems
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FM Stereo Transmitter

• Transmitter Output
• Main Channel (L R)
• Stereo Channel (L - R)
• 19 kHz Pilot Sub-carrier

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Stereo Multiplexing

• LR Signal (Main Channel)
• L-R Signal (Stereo Channel)
• 19 kHz Pilot Subcarrier (FM)

The Math (L R) (L - R) 2 L (L R) (- L
R) 2 R
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FM Stereo Receiver
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Television Stereo

• Multi-channel Television Sound (MTS)
• Used to provide Stereo on conventional NTSC TV
  broadcast (TV has been FM mono for most of its
  history)

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Television Transmission Systems
Over-the Air Terrestrial Broadcasting
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Antenna Systems

• Radio Energy in Space
• 300 million meters per second
• E MC2
• Speed of Light

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Spectrum
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Wavelength

• Lambda (meters)
• Velocity (300,000,000 meters/sec.)
• Frequency (Hz)
• ? v/f

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TV Station
WTHR-TV Ch.13 (210-216 MHz)

• WAVELENGTH IN
• Meters
• Miles
• Feet

WTHR-TV
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WTHR Television - Channel 13 Indianapolis, Indian
a

• Channel 13 (210-216 MHz)
• 316 kw visual
• 63.2 kw aural
• 980t/1,039g
• Television Factbook
• 47 CFR 73.603

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Wavelength Example WTHR Television
Meters Lambda 300/211.25 1.46 meters
Miles Lambda .186/211.25 .00088 miles
Feet 1 meter 3.28 feet Lambda 1.46 meters
x 3.28 4.79 feet
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AM Station

• What is the height of this AM station antenna
  tower operating at 540 kHz, in meters and feet?

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Propagation

• Radiation Patterns (Contours)
• AM - Tower as the Antenna
• FM/TV - Antenna on Tower

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TV Propagation
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TV Propagation Map
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FM Propagation Map
KFMD-FM Denver
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AM Tower
Side view
Top view
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AM Directional Towers
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AM Directional Propagation
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Irregular Geographical Patterns

• Refraction
• Reflection
• Absorption
• Interference

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Why Directional Arrays?

• Co-Channel
• Adjacent Channel
• Other

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Types of Waves

• Direct Waves (FM/TV)
• Ground Waves (AM)
• Radials
• Swampy Soil vs. Sandy Terrain
• Sky Waves (AM at night)

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Types of Waves
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Direct Waves
The primary path of the direct wave is from the
transmitting antenna to the receiving antenna.
So, the receiving antenna must be located within
the radio horizon of the transmitting antenna.
Because direct waves are refracted slightly, even
when propagated through the troposphere, the
radio horizon is actually about one-third farther
than the line-of-sight or natural horizon.
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Direct Waves
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Ground Waves
The Earth has one refractive index and the
atmosphere has another, thus constituting an
interface that supports surface wave
transmission. These refractive indices are
subject to spatial and temporal changes.
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Ground Waves
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Sky Waves
Sky waves, often called ionospheric waves, are
radiated in an upward direction and returned to
Earth at some distant location because of
refraction.
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Sky Waves
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Questions and Answers