Imagen perfecta de los sistemas AV

9 de mayo de 2018 / General

Ya sea videoconferencia o señalización digital, es probable que muchos de ustedes se enfrenten a solicitudes de sus clientes para desplegar plantas de cable que soporten sistemas audiovisuales.

Many of these applications utilize HDBaseT or IP-based video transmission, and technology advancements now make it possible to deliver power to video displays simultaneously with these video signals over the same cabling. Cuando se trata de implementar y probar las instalaciones del cableado necesarias para soportar estos sistemas AV, es importante entender las mejores prácticas de prueba para garantizar que sus clientes obtengan la imagen perfecta que esperan.

Different Protocol, Same Concerns, One Tester

HDBaseT is a consumer electronic and commercial connectivity standard for transmitting uncompressed 4K video signals, audio, 100BaseT Ethernet data, power and various control signals over common category copper cabling up to 100 meters. Si bien esto es similar a los sistemas de video basados en IP, y el cableado y la conectividad pueden parecer iguales, los dos son protocolos realmente diferentes. Unlike IP-based video that runs over the data network using packet-based Ethernet via common network switches and routers, HDBaseT is not packet based and instead uses HDBaseT transmitters and receivers that are separate from the data network.

But don’t let this worry you. Since both HDBaseT and IP-based video run over the same cabling media used for data transmission, they are deployed using the same best practices and are subject to the same performance parameters. So if Category 6A cable is deployed for either HDBaseT or IP-based video, it must be certified to meet the TIA Category 6A standard – especially if you want to receive the manufacturer's warranty.

One performance parameter that matters most when it comes to achieving a perfect picture is propagation delay skew. Propagation delay (expressed in nanoseconds) is the amount of time it takes for a transmitted signal to be received at the other end of the link or channel. Propagation delay skew is propagation delay that differs from one pair to another in a four-pair twisted-pair cable. For high-resolution RGB video signals where each color is sent down a separate pair, too much delay skew can cause a jittery picture on a video displays. That’s why cabling vendors tout their “low skew” cables as ideal for video applications.

Something else common to both HDBaseT and IP-based video systems is that both can now transmit higher levels of DC power using all four pairs of a twisted-pair cable—one using power over HDBaseT (POH) and the other using power over Ethernet (PoE). POH ofrece hasta 100 W de potencia de CC en cuatro pares junto con las señales de video HDBaseT, mientras que PoE ofrece hasta 60 W (Tipo 3) o 90 W (tipo 4) de alimentación de CC a través de cuatro pares junto con la señal de video basada en IP. These power levels are enough to power typical LED video displays, eliminating the need for AC power.

This also means that both systems come with the same concerns inherent when running higher DC power over all four pairs, such as insertion loss caused by heat rise and DC resistance unbalance caused by poor workmanship or subpar cable quality. La entrega de POH o PoE se logra al aplicar un voltaje de modo común que divide uniformemente la corriente entre cada conductor en los pares, lo que requiere que la resistencia de CC de cada conductor sea igual. La diferencia en la resistencia entre dos conductores es el desequilibrio de resistencia de CC, y una gran parte de ella puede provocar que las señales de video se distorsionen. Con los cuatro pares de potencia de transmisión, también es importante el desequilibrio de resistencia de CC entre múltiples pares.

The good news is that a Fluke Networks DSX CableAnalyzer™ Series copper cable certifier will do it all to make sure your customer’s AV systems are picture perfect. Not only will it will certify cabling plants to industry standards for both HDBaseT and IP-based video deployments, including propagation delay and delay skew, but its ability to test for DC resistance unbalance can also verify the ability of the cable plant to support POH and PoE.

To learn more about testing AV systems, Read White Paper: Consideraciones de cableado de audio/vídeo (AV)

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