Understanding Video Signal Synchronization and Components
B) Signs of Synchronization. For beneath the black level of them are located synchronization impulses. There are two basic types: • Synchronization dial pulses (horizontal synchronization pulses). These are sent during return line intervals and serve to indicate the transition between two lines of television. • Pulse of frame (vertical synchronization pulses). These are sent during return block intervals and serve to identify the time when a frame begins and ends.
How is the point of deflection fastest horizontally than vertically? It will trace a succession of horizontal lines on the screen called deflection lines. A complete horizontal deflection (A to B) is called line sweep, while the return from B to A is called the return line. The return from C to D is the return block. In the PAL system, we have 625 lines between both fields, of which 575 contain image information (the rest are either blank or do not contain information used by the synchronization pulses).
The video signal is an electrical signal of 1 volt, corresponding 0 – 0 V to the image and synchronization signs.
Between 0 V and 0.7 V, we can find the black and white of the image, so above these limits, any excess will be electronically removed and reproduced as
total white or total black. (The softness or abrupt tonal gradations depend on the system. When you have a range of 1, the level of the video signal is proportional to the image; if the range has a floor (for example, below 1, such as 0.65), the result will be a soft tonal contrast; otherwise, if it is high (above 1, such as 2.2), it will produce an abrupt, exaggerated tonal contrast).
As we know, the luminance signal can be obtained by summing the components of red,
green, and blue, which is how it works in the analog systems of color television. However, since the human eye responds to all colors, this sum must be correctly combined in the following proportions:
Y (luminance) = 0.299 R (Red) + 0.587 G (Green) + 0.114 B (Blue).
This signal is then processed separately for use by black and white televisions.
To reduce the bandwidth for use by color (and maintain compatibility with black and white TVs), the chrominance components RGB are not used separately, but are obtained through signals that respect the difference of color luminance. These are the signals
that subtract the result of the luminance signal (Y) from the primary signals of red (R) and blue (B), and only two can be deduced from the other two. These two signals are called chromatic signals
U and V, and are defined as U = (R – Y) and V = (B – Y), from which the combined signal generates a unique signal called Chrominance.
[In reality, both are weighted to reduce their level, so the definitive values for this signal are: U = 0.493 (B – Y) and V = 0.877 (R – Y)].
In the color systems NTSC, PAL, and SECAM, the luminance and chrominance signals combine to form a complete video signal, although there are differentials between them based on how the chromatic signal is processed.
III. Control and Adjustment of the Video Signal
The most relevant measurement equipment for the analysis of video signals are the following: a) Waveform monitor (or MFO). A monitor is a waveform oscilloscope calibrated to measure a video signal. While the basic function of an oscilloscope is to capture and graphically represent time-varying electric tensions, the MFO has a base designed to adapt to the typical video signal’s time. Its screen has marks and reference lines tailored for signal amplitude and time TV, which allows us to visualize the general luminance (brightness) values of an image.
B) Vectorscope. This is a specialized oscilloscope for measuring and visualizing parameters of the chrominance signal (in general, it is also a waveform monitor). Corresponding vectors represent the different colors contained in the video information, as well as the synchronization serving as a reference phase. The screen displays a circular grid marked with areas where the vectors will appear, forming colors that correspond to the reference color used in the measurements. These areas are identified with the initials of the corresponding colors in Spanish, and their entries are based on a cross indicating the exact points of phase and amplitude for each color.
C) Spectrum analyzers. A spectrum analyzer allows for analyzing signals based on frequency. It is useful for analyzing the television signal modulated on a radio frequency TV channel, allowing the distribution check of luminance, chrominance, and accompanying sound signals.
An important element associated with the adjustment of the video signal in television studios is the camera control unit (CCU). Besides acting as a remote control, the CCU allows for adjusting the video signal subcarrier phase and color (to synchronize the camera equipment with all other studio equipment) and adjust the controls of the following cameras: iris (aperture of the diaphragm), master pedestal, and the pedestal of R, G, and B independently, gain R, G, and B independently, gain E (0, 9, 18 decibels), automatic control of black and white balance, storage and recovery of camera memories, color generation, etc. Most video cables use coaxial cable, which is designed to carry high-frequency electrical signals and consists essentially of two concentric conductors: a central or core conductor, formed by a solid or braided copper wire (called positive or live), and an external conductor or sheath that is formed by a braided copper mesh, which generally also serves as a reference for ground and return currents. Both conductors (and the braided mesh) are separated from each other by an insulating layer, and the entire assembly is usually protected by a protective cover. The most common types of video connectors are the following: • BNC connector. This is a male type connector for quick docking with a ring that rotates on the external part of the connector to ensure access to any female BNC connector. The connection panels incorporate connections for both input and output, so the wires are always equipped with male BNC connectors on both ends. They are mainly used for transporting analog signals in the most common analog TV equipment: the composite video signal (luminance and chrominance combined) and the three components separately in analog (luminance signal and color differences, YUV). • Y/C connector (Separate Video, S-Video). This is a 4-pin connector that leads luminance and chrominance signals modulated separately, which provides the highest quality by increasing bandwidth and reducing color interferences. • RCA connector. This is a type of connector commonly found in the audiovisual market, used for both audio and video connections in non-professional settings. It serves as an alternative to the BNC connector for video transport. • Euroconnector (SCART). This is a non-professional, 21-pin connector that allows for the transport of a variety of audio and video signals, including composite video, chrominance and luminance separately, and RGB signals. • RF connectors. These are the antenna connectors and coaxial connectors used in devices that feature radio frequency input and/or output. The outputs are male and female connectors, allowing the connection cables to have one end male and the other female (macho-hembra connection). • Multicore cable (or multipin). The multicore cable is a cable grouping several (14 or more) conductors inside a sheath or tube. It is commonly used in camera chains for connection to CCUs (transporting audio signals, video, tally, power, and remote camera control). These cables are complex, and each manufacturer employs a different type, making them relatively expensive. • Triax. This is a cable composed of a concentric center conductor and two conductors that provides a more economical and equally functional alternative to multicore cables, although it is universal and easier to build and repair (and therefore cheaper), it is required for technology in the most expensive cameras, so it is only available in high-end equipment.