I recently bought a cheap 3quid hdmi extension cable for my oculus rift. It's been causing screen tear. I know what cables are compatible now but I'm wondering what affects the bandwidth of a cable?
If the wavelength of the signal you want to transport over the cable is short compared to the length of the cable (so many waves "fit" inside the cable) then we should consider the cable to be a transmission line.
There is more going on than just the bandwidth. To transport a signal properly through the cable the cable has to behave as a proper transmission line. Things that can go wrong are:
- the cable attenuates the signal (very much related to bandwidth)
- the characteristic impedance of the cable is not what it should be
- the connectors do not match well to the cable causing a change in characteristic impedance which causes signal reflections
Since your problematic cables are extension cables it is very likely that the extra connectors cause reflections of the signal. Depending on what type of signal you're using (HDMI supports several data rates) these reflections can cause problems or not. For example it might be that at a lower resolution / framerate the cables work just fine.