Fundamentals of Television Signals
Differences: Interlaced vs Non-Interlaced Scan
Interlaced: The lines of the image are displayed on the screen by interleaving pairs on one side and odd on the other side.
Non-Interlaced: The lines are all displayed in order.
Differences Between Lines, Field, and Image
The image is divided into horizontal lines; each of these horizontal lines consists of points.
Why a Field Has 312.5 TV Lines
This is explained for several reasons. The first is that each field appears in the middle of the first line and ends in the middle of the last, so these first and last lines do not contain all the information in its entirety. This indicates that the two constituent fields will not be exactly alike.
Most Common Video Signal Measurement Equipment
Oscilloscope.
Amplitude Level of a Standard Video Signal
1 volt.
Video Signal Amplitude Range: Image vs Sync
Image Information: Between 0V and 0.7V
Synchronization: -0.3V
Basic Parameters of an Image Element
- Brightness: Indicates the intensity of the point.
- Hue: Represents the pure color of the point.
- Saturation: Defines the amount of color in the point.
Vertical Sync Pulses and Duration
There are 5 pulses of 32 µs each, making a total of 160 µs for the 5 pulses.
Structure of the Horizontal Blanking Period
Signals Forming a Complete TV Picture
Signals that form a complete TV picture, in order of appearance:
- Vertical synchronization pulses.
- Post-equalizing pulses.
- Lines without video information.
- Lines with video information.
- Pre-equalizing pulses.
Why an Electronic Module is Needed to Transmit a Signal
A television signal contains a wealth of information to be processed together. To avoid interference between its different components and to set different carrier frequencies, modulation is used.
The Phenomenon of Modulation Explained
The concept of modulation can be defined as the systematic alteration of parameters of a signal, called the carrier, depending on how the amplitude of another signal, which contains the message, called the modulator, varies.
Modulations Appearing on a Television Channel
- Amplitude modulation.
- Vestigial sideband modulation.
- Double-sideband modulation.
- Frequency Modulation.
- Phase-shift keying.
Number of Bands Used in Terrestrial TV Broadcasting
Four bands.
Terrestrial TV Broadcasting Bands
- Band I: From 47 MHz to 68 MHz.
- Band II: 85.7 MHz. From the 108 MHz to MHz.
- Band III: From 174 MHz to 230 MHz.
- Band IV: From 470 MHz to 606 MHz.
- Band V: From 606 MHz through 862 MHz.
Spectrum Analyzer Expansion Factor
Defines the frequency range above and below the plant that appears in the rendered image.
Orientation of Fields in an Electromagnetic Wave
Electromagnetic waves are transverse; the directions of the electric and magnetic fields are perpendicular to the direction of propagation.
Utility of the Acoustic Signal in Field Meters
So the technician can work without having to look at the screen, as the equipment emits a beep where the more power received, the higher pitched the sound.
Types of Electromagnetic Wave Propagation
- Surface wave propagation: The wave follows the surface of the earth from the transmitter to the receiver.
- Ionospheric reflection propagation: The wave is sent to a point in the ionosphere and reflects back to the receiver.
- Direct-wave propagation: The wave travels directly from the transmitter to the receiver.
Parameters of an Electromagnetic Wave
- Period: The time taken for a signal to complete one cycle.
- Wavelength: The distance the wave travels during one cycle of the signal.
- Velocity of Propagation: Electromagnetic waves propagate at 300000 km/s.
- Frequency: The number of signal cycles completed in one cycle.
- Power: The amount of energy the signal carries.
Width of a TV Channel in Band IV
8 MHz.