Active vs. Passive Solutions

Extension and distribution devices that utilize UTP cabling, i.e. Cat5, Cat5e, Cat6, etc., require that the A/V input signals be changed so that they may be sent through a balanced system. Changing from a single–ended system, which is typical of an A/V application, to a balanced system, which is typical of an over UTP extension solution, can be accomplished passively — by using a transformer, or actively — by using amplifiers and active devices.

Using a passive method is often very inexpensive and can leverage existing cabling infrastructure. The transformer used in these devices is basically a small, round ferrite that is wrapped with pieces of copper wire. The transformer turns–ratio dictates operation, how those wires are layered and how many times they are twisted. Passive devices are not precision devices. They neither match impedances well nor match the mirrored positive and negative signals well, and they are unable to compensate for variation in signal frequencies or cabling length. Due to the nature of the design of this type of product, there is an ideal length of cabling that is meant to be used between the source and display end. Variations from that length will deteriorate the performance. Most passive devices are designed to operate at a length between 50 and 75 feet. Because these devices are passive, there is no ability to adjust for different lengths of cabling. Also, the performance of these devices will vary depending upon manufacturing tolerances. While the use of passive solutions is a good way to inexpensively convert into a twisted pair environment, it is not the best way to extend or distribute signals.

Active conversion to twisted pair is superior to passive conversion because it uses matched active devices and also offers equalization. An active extension or distribution device with equalization essentially moves the signal backward and forward in time based on the skew of the pairs in UTP cabling. The construction of UTP cabling calls for differing twist per inch in each of the pairs. This difference in twisting can lead to a 10–15% variation in the length of the different pairs over a 100 foot cable. Because electricity takes a finite amount of time to travel over the conductors in the cable — and as the length in the UTP cabling increases, the delay/skew increases — equalization allows the different parts of the video signal to be realigned. This allows active devices to display high quality images over long distances to the monitor or multiple monitors.

Active vs. Passive Solutions

This white paper is for informational purposes only and is subject to change without notice. C2G makes no guarantees, either expressed or implied, concerning the accuracy, completeness or reliability of the information found in this document.