User Guide

Crestron Quick Guide to Touchpanel Connections

QuickMedia Installation Notes

The QuickMedia transport mechanism performs delay compensation on each

video input to compensate for signal skew, and frequency/bandwidth

compensation for cable length. Signal skew occurs when part of the signal is

delayed with respect to other signal components. The amount of skew largely

depends on the length and design of the wire. Because CAT5 consists of

twisted pairs that are twisted together in the cable, unequal wire lengths are

created.

The maximum aggregate cable length from QM transmitter to QM receiver is

limited by the loss of bandwidth over long distances and the amount of

available skew compensation. A cable rated at 15 ns of skew per 100 meters

(328 ft.) means that a cable will have no more than a 15 ns difference

between the fastest and slowest RGB signals over 100 meters of cable.

To determine the allowable maximum length of installed cable, the installer

must first perform a calculation based on the skew rating of the cable. The

use of low-resolution signals may allow increased cable length but must be

tested with the sources to be used. To ensure sufficient bandwidth to support

signal resolutions up to 1600 x 1200, the maximum aggregate cable length

should not exceed 328 feet.

Skew compensation is primarily relevant to RGB sources; however, any/all

video or VGA signals may experience a loss of quality over very long lengths

of cable. This phenomenon is due to the added resistance and capacitance of

longer cable lengths, and is not particular to either Crestron and/or

QuickMedia systems.

The total accumulated skew from QM transmitter to QM receiver must not

exceed 15 ns (nanoseconds). Crestron recommends a cable with a rating of

less than or equal to 15 ns over its entire length. For example, if using a cable

with a rating of 15 ns/100 meters (100 meters = 328 feet), connecting the

QM-FTCC transmitter with 150 feet of cable to a QM-MD7x2 switcher, and

then using another 150 feet to connect the QM-RMCRX-BA receiver, the

accumulated skew over the entire 300 feet should not exceed 15 ns.

Crestron Quick Guide to Touchpanel Connections Doc. 4903