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»The future is HDTV

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Digital revolution, digital audio and video specifications, return loss, the basic rules of choosing cables...

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DIGITAL REVOLUTION
 
We are in the middle of digital revolution, both radio and television broadcasters are going to digital. This will create a demand for the fidelity that HDTV can achieve. HDTV requires highest technologic cables and connectors. With this bulletin we intend to inform you about basic topics that you need to know.
 
DIGITAL AUDIO AND VIDEO STANDARDS
 
Data Transmission Speed
Bandwidth
Standard
Definition
143 Mb/s
71,5 MHz
SMPTE 259M
NTSC
177 Mb/s
88,5 MHz
ITU-R BT.601
PAL/SECAM
270 Mb/s
135 MHz
SMPTE 259M
Component Video 4:3
360 Mb/s
180 MHz
SMPTE 259M
Component 16:9
540 Mb/s
270 MHz
SMPTE 344M
Component  Widescreen
1,485 Gb/s
742,5 MHz
SMPTE 292M
HDTV
 First of all we need to explain “DTV” term. Analogue signals convert to digital signals. Digital video signals consist of different coloured points called “pixel”. Resolution is the term for the number of pixels. The bigger this value is the better definition. Digital systems need high frequency values because they are very complex signals and use binary coding. SDTV-SDI transmission speed is 270Mpb where HDTV-SDI is 1,485Gbps.
The society of Motion Picture and TV Engineers (SMPTE) have developed several standarts for serial digital video transmissions (SDI) and a 540Mb/s format is currently under development. There is also a European standarts body known as the ITU that developed the composite video standart for Europe known as PAL/SECAM. You may find the different standarts at the table below.
 
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RETURN LOSS
 
Return Loss is also an important factor of transmitting signals. RL is a signal attenuation caused by impedance variations in the structure of a cable associated connection parts. The variations cause the signal to reflect(return) back to the source. At low frequencies above 50Hz, it can have a significant effect; and at frequencies used for high definition video, 1500Mhz and higher, it can be a major even critical factor. For this reason it is suggested that return loss be a key consideration in the measurement and verification of HD system performance.
SMPTE recommends that return loss should be at least -15dB at 1.485GHz.

CONNECTOR CHOICE
 

75Ω control cables are the best choice for the transmission of digital signals. But it must be used with BNC connectors. The return loss is 26db or less for frequencies up to 2GHz in 75Ω coaxial cables using 75Ω BNC connectors. If 50Ω BNC connectors are attached to both end of the same cable, the RL takes on characteristics when frequencies exceed 100MHz.