HD-SDI(2): Transmission extendable in distance

HD-SDI(2): Transmission extendable in distance

Transmission distance and quality of coax will determine the performance of the surveillance system. a&s goes beyond the camera and takes a peek at where back end products currently stands.

A major advantages of HD-SDI technology is the existing infrastructure which could potentially be reused. The coax can still be kept in place, which saves time and cost of installation. However, HD-SDI solution will not work with “just any” coaxial cable. Since HD-SDI is digital, it does not degrade like analog does, according to Todd Rockoff, Executive Director, HDcctv Alliance. Installers bidding retrofits will need field testers to verify the status of the cables.

Length Does Matter
The valid distance a video signal on coax will go without a need of a repeater varies based on cable types, the integrity of the insulating layers, SMPTE standards, camera chips, and so forth.

HD video uses more bandwidth throughput than analog cameras, installers must use RG59 or better coax. Pre-made cables that are a thinner gauge than RG59 will not be able to transmit the video signal effectively. It is also recommended to use a high quality 95 percent or better copper cable. Great quality cables also minimize impedance issues. 5CFB, 5C2V (RG-59U), or RG-6 cables with at least 192 braid better avoid signal loss and data transmission interference. The effective distance that a video signal can transmit over RG59 cable is 120 to 140 meters (300-350 feet) without the use of an HD-SDI transmission extender. In order to transmit 3G-SDI videos at 1080p 60fps, the cables must meet SMPTE259M/424M-2006 standard.

HD-SDI repeaters or fiber optic transceivers can be used to extend the transmission distance of HD-SDI signals. When selecting repeaters, it is advisable to note camera compatibility.

Speed of Light
There are plenty of attempts to place HD-SDI cameras on fiber such as transceivers with WDM/DWDM/CWDM to utilize different wavelengths of light to extend signal reach. Multiple channels can be put on one fiber and this will involve using different optical wavelength channel, one for each channel using CWDM technology. DWDM, on the other hand, allows voice, PTZ, and RS422/485 signals for bi-directional control.

Still No Wireless
Wireless is still not feasible for HD-SDI solutions. A SDI digital video server could be adopted in order to transport video streams over the network.



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