Broadcast Basics

Week 13

ICS 620

BROADCAST BASICS

ICS 620

Week 13

Introduction

Video Basics (Analog Systems)

Transmission Systems

• Wireless (terrestrial)

• Wired (cable television)

Digital Video (Two Weeks)

Video Standards

• Standards and Principals

– Persistence of Vision

The rapid presentation of frames of video information to give you the illusion of smooth motion.

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

Frequency Standards

Field Frequency

• Frame Frequency x 2

• Continuity of Illumination

Film Vs. Video

• Film - Project a complete picture

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

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”)

Vertical Resolution

• The picture quality associated with the number of dots (pixels) used to construct the picture.

– 367,000 dots

– on 525 rows (vertical)

Film vs. NTSC Specs

Aspect Ratio

Camera TubesCamera Tubes

Early Camera Tubes

Image Orthicon

Electronic Scan(Camera Pickup Tube)

Video Signal

Electron Beam

TargetLensObject

Scanning

• Progressive

• Interlace/Offset

Interlace Example

NTSC: 525 lines, 30 frames/sec,

60 fields/sec

Picture TubePicture Tube

Picture Tube

Picture Tube

Scanning a Focused Image

Progressive Scanning

Interlace Scanning

Sync Pulses

Differences Between Horizontal and Vertical Synch Pulses

Rate Duration

Vertical 59.94/sec 1:3

Horizontal 15,734.264/sec 3:1

Waveform Sketch of a Video Signal

A simple videoA simple video waveformwaveform

One Line

Waveform of Sync Pulses

IRE Measurement Scale

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)

Kell Factor

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

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

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

Television Transmission

• Picture Information

• Blanking pulses

• Sync pulses

• Audio information

What about Color?

Component Nature of ColorComponent Nature of Color

R

G B

Video Color Palette

Color Television

R = Red

G = Green

B = Blue

B + G = Cyan

G + R = Yellow

B + R = Magenta

NTSC Color BarsNTSC Color Bars

Block Diagram of Color Camera

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.

Composite Color

• Y = Luminance SignalY =30% red + 59% green + 11% blue

• C = Chrominance SignalC = I Q Matrix

Color Matrix

• Saturation = Amplitude of the I and Q signals

• Hue = Phase developed by the difference in amplitude between the I and Q signals

Transmitter TubeTransmitter Tube

Color TV Transmitter

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.

NTSC Bandpass Characteristics (Black and White)

Color TV Signal

NTSC Bandpass Characteristics (Color)

Color TV Signal

Worldwide Standards

• National Television System Committee - NTSC (1953)

• Phase Alternation Line -PAL (1967)

• Sequentiel Couleur Avec Memoire - SECAM (1967)

World TV Standards

World TV Standards

Principal TV Systems

FM Stereo Transmitter

Transmitter Output

• Main Channel (L + R)

• Stereo Channel (L - R)

• 19 kHz Pilot Sub-carrier

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

FM Stereo Receiver

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)

Television Transmission Systems

Over-the AirOver-the Air

Terrestrial BroadcastingTerrestrial Broadcasting

Antenna Systems

• Radio Energy in Space

–300 million meters per second

• E = MC2

• Speed of Light

Spectrum

Wavelength

• Lambda (meters)

• Velocity (300,000,000 meters/sec.)

• Frequency (Hz)

= v/f

TV Station

WTHR-TV

WTHR-TV

Ch.13 (210-216 MHz)

WAVELENGTH IN:

A. Meters

B. Miles

C. Feet

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

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

AM Station

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

Propagation

• Radiation Patterns (Contours)

• AM - Tower as the Antenna

• FM/TV - Antenna on Tower

TV Propagation

TV Propagation Map

FM Propagation Map

KFMD-FM Denver

AM Tower

Side view Top view

AM Directional Towers

AM Directional Propagation

Irregular Geographical Patterns

• Refraction

• Reflection

• Absorption

• Interference

Why Directional Arrays?

• Co-Channel

• Adjacent Channel

• Other

Types of Waves

• Direct Waves (FM/TV)

• Ground Waves (AM)– Radials

• Swampy Soil vs. Sandy Terrain

• Sky Waves (AM at night)

Types of Waves

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.

Direct Waves

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.

Ground Waves

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.

Sky Waves

Questions

and

Answers