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CCIR System B
CCIR System B (originally known as the "Gerber Standard") was the 625-line VHF analog broadcast television system which at its peak was adopted by more than one hundred countries, either with PAL or SECAM colour. It is usually associated with CCIR System G for UHF broadcasts.
System B was the first internationally accepted 625-line broadcasting standard in the world. A first 625-line system with a 8 MHz channel bandwidth was proposed at the CCIR Conference in Stockholm in July 1948 (based on 1946-48 studies in the Soviet Union by Mark Krivosheev). At a CCIR Geneva meeting in July 1950 Dr. Gerber (a Swiss engineer), proposed a modified 625-lines system with a 7 MHz channel bandwidth (based on work by Telefunken and Walter Bruch), with the support of Belgium, Denmark, Italy, Netherlands, Sweden, and Switzerland. Known as the "Gerber-norm", it was eventually approved along with four other broadcast standards on the next formal CCIR meeting in May 1951 in Geneva.
In the 1960s, the capital of Mexico, Mexico City decided to replace System B with 525-line CCIR System M, despite the recommendations of Guillermo González regarding the technical advantages of System B.
It is mostly replaced across Western Europe, former Yugoslavia, parts of Asia and Africa by digital broadcasting.
The system was developed for VHF (also known as VHF-3) band (part of RF band lower than 300 MHz.) Some of the most important specs are listed below:
A frame is the total picture. The frame rate is the number of pictures displayed in one second. But each frame is actually scanned twice interleaving odd and even lines. Each scan is known as a field (odd and even fields.) So field rate is twice the frame rate. In each frame there are 625 lines (or 312.5 lines in a field.) So line rate (line frequency) is 625 times the frame frequency or 625×25=15625 Hz.
The video bandwidth is 5.0 MHz. The video signal modulates the carrier by amplitude modulation. But a portion of the lower side band is suppressed. This technique is known as vestigial side band modulation (AC3). The polarity of modulation is negative, meaning that an increase in the instantaneous brightness of the video signal results in a decrease in RF power and vice versa. Specifically, the sync pulses (being "blacker than black") result in maximum power from the transmitter.
The primary audio signal is modulated by frequency modulation with a preemphasis time constant of = 50 μs. The deviation for a 1.0 kHz. AF signal is 50 kHz.
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CCIR System B
CCIR System B (originally known as the "Gerber Standard") was the 625-line VHF analog broadcast television system which at its peak was adopted by more than one hundred countries, either with PAL or SECAM colour. It is usually associated with CCIR System G for UHF broadcasts.
System B was the first internationally accepted 625-line broadcasting standard in the world. A first 625-line system with a 8 MHz channel bandwidth was proposed at the CCIR Conference in Stockholm in July 1948 (based on 1946-48 studies in the Soviet Union by Mark Krivosheev). At a CCIR Geneva meeting in July 1950 Dr. Gerber (a Swiss engineer), proposed a modified 625-lines system with a 7 MHz channel bandwidth (based on work by Telefunken and Walter Bruch), with the support of Belgium, Denmark, Italy, Netherlands, Sweden, and Switzerland. Known as the "Gerber-norm", it was eventually approved along with four other broadcast standards on the next formal CCIR meeting in May 1951 in Geneva.
In the 1960s, the capital of Mexico, Mexico City decided to replace System B with 525-line CCIR System M, despite the recommendations of Guillermo González regarding the technical advantages of System B.
It is mostly replaced across Western Europe, former Yugoslavia, parts of Asia and Africa by digital broadcasting.
The system was developed for VHF (also known as VHF-3) band (part of RF band lower than 300 MHz.) Some of the most important specs are listed below:
A frame is the total picture. The frame rate is the number of pictures displayed in one second. But each frame is actually scanned twice interleaving odd and even lines. Each scan is known as a field (odd and even fields.) So field rate is twice the frame rate. In each frame there are 625 lines (or 312.5 lines in a field.) So line rate (line frequency) is 625 times the frame frequency or 625×25=15625 Hz.
The video bandwidth is 5.0 MHz. The video signal modulates the carrier by amplitude modulation. But a portion of the lower side band is suppressed. This technique is known as vestigial side band modulation (AC3). The polarity of modulation is negative, meaning that an increase in the instantaneous brightness of the video signal results in a decrease in RF power and vice versa. Specifically, the sync pulses (being "blacker than black") result in maximum power from the transmitter.
The primary audio signal is modulated by frequency modulation with a preemphasis time constant of = 50 μs. The deviation for a 1.0 kHz. AF signal is 50 kHz.