Originally Posted by Lazypants
I hope you all noted that the unit at http://www.lenexpo-electronics.com/A...r-p-17468.html
(like many of the other extender units (including Gefen)) recommend using shielded cat5/6 for best picture quailty. I posted a question on this forum regarding the shielded cable requirement but got no response. I would like to know from one of the great many technically proficient readers on this forum why the shielded cable is needed and how much degradation in the video signal will occur if a shielded cable is not used.
I can't say for certain but I can probably guess....
If you take the traditional component balun as an example, it is converting an unbalanced signal to a balanced signal. When using straight component that is why coax with heavy shielding is preferred because it reduces the possiblity of RF noise being induced onto the signal. Unbalanced signals are referenced to ground, so any noise will distort the video. Balanced on the otherhand benefits from noise cancellation and the inherent properties of a Cat5 cable. When noise makes its way onto a Cat5 cable running a balanced signal, the noise is cancelled out because it is equally induced onto each wire of a twisted pair.
So for example, if you have a steady 5VDC signal on an unbalanced cable, that 5VDC is referenced to ground (0VDC). So the receiving unit is expecting a 5VDC amplitude. However, along the way, 100mv of noise is induced. Since ground is always 0VDC, the receiving unit now receives 5.1VDC and the signal is no longer the same as what the sending unit sent.
On the contrary, take a balanced cable. The same 5VDC signal is sent. 0VDC gets sent on one wire of the pair and 5VDC gets sent on the other. Along the way, 100mv of noise is induced. One wire has 0.1VDC and the 2nd wire has 5.1VDC. But the difference between the two is 5VDC so the signal is intact.
With component baluns, this works very well because the translation is 1:1 in wire conductors. The balun takes two wires (ground + Signal) from the unbalanced side and converts it to two wires (Signal Differential) on the balanced side. Since component takes 6 conductors, it is easy to use 6 of the 8 conductors on a cat5 cable. No trickery here. Its why you mostly see component + 2ch audio baluns requiring two cat5s. There simply aren't enough conductors.
With HDMI baluns, and this is where it gets muddy and I'm only guestimating, it's a different story. HDMI requires 19 wires. So that lowly balun which uses only 8 wires of a cat5 cable has to somehow get the signals from 19 wires in/out. How they are doing this, I'm not sure. If they are converting everything to digital packets, encoding on one end and decoding on the other, then it shouldn't require STP (shielded), but there may be a bandwidth issue at this point. So maybe they are cheating and some of the signals they are still sending as unbalanced which are of course susceptible to noise. So, they recommend shielded Cat5.