Model UVA-4 and UVA-8
8
3.4 Why Skew Adjustment?
UTP cables have 4 twisted pairs inside. The Hall Research UVA/URA video
transmission on UTP uses 3 individual pairs for each color (Red, Green, & Blue).
Figure 5 - skew mechanism, example
As shown in the figure above, a characteristic of CAT5/5e/6 cable is that the pairs of
wires twist at different rates.
Therefore, for a given length of CAT5/5e/6 cable the total length of any particular
pair could be longer than other pairs in the same cable. Since the signals travel
along the length of each pair at a fixed speed, the arrival times of signals will be
skewed in a long cable (those that have to travel farther arrive later and the
corresponding color shifts to the right). This is viewed on the monitor as separation,
or lack of convergence in colors. For example, a vertical white line on the screen
may look to have a red tinge on the left edge and blue tinge on the right edge. This
effect gets worse at high resolutions, high refresh rates, long cables (in excess of
200 feet), and depends on the cable construction itself.
If you are using special UTP cables that are specifically designed for video
transmission (such as Hall Research Zero-Skew™), then there should be no shift in
color alignment regardless of the cable length. However, in many applications
standard and common CAT5/5e/6 cables can be utilized, this will necessitate a
receiver that can also move each color component to the left and right in order to
realign them.
300 ft of CAT6 (1280x1024 source)
* actual zoomed photo of screen *
After skew adjustment
Figure 6 – Example of Skew manifested
