broadcast basics week 13 ics 620. broadcast basics ics 620 week 13
TRANSCRIPT
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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 Standards
Frame 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 Standards
Field 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 TubesCamera Tubes
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Early Camera Tubes
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Image Orthicon
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Electronic Scan(Camera Pickup Tube)
Video Signal
Electron Beam
TargetLensObject
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Scanning
• Progressive
• Interlace/Offset
Interlace Example
NTSC: 525 lines, 30 frames/sec,
60 fields/sec
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Picture TubePicture 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 1:3
Horizontal 15,734.264/sec 3:1
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Waveform Sketch of a Video Signal
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A simple videoA simple video waveformwaveform
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 ColorComponent 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 BarsNTSC Color Bars
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Block Diagram of Color Camera
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Gamma
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 SignalY =30% red + 59% green + 11% blue
• C = Chrominance SignalC = 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 TubeTransmitter 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 and 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
• L+R 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 it’s history)
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Television Transmission Systems
Over-the AirOver-the Air
Terrestrial BroadcastingTerrestrial 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
WTHR-TV
Ch.13 (210-216 MHz)
WAVELENGTH IN:
A. Meters
B. Miles
C. Feet
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WTHR Television - Channel 13Indianapolis, Indiana
• Channel 13 (210-216 MHz)
• 316 kw visual
• 63.2 kw aural
• 980t/1,039gTelevision Factbook
47 CFR 73.603
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Wavelength ExampleWTHR 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