Cable Impedance

Generally, most audio-video cables are 75ohms, mainly because it has become a standard cable type for audio and video systems.

These are as follows:-

• Analogue UHF (Ultra high frequencies) and VHF (Very high frequencies) Video cable

• Balanced and unbalanced audio cable

However digital cable would tend to use 110ohm cable for these situations: –

• AES-EBU which is also balanced

• CAT5 or CAT6 Ethernet.

• Digital video

It is important to use the correct impedance cable with the same impedance connectors.

Note:

You start to notice the effects of impedance with RGB video, where a separate cable is used for each individual component R (Red) G (Green+sync) B (Blue), as Green sends a sub of both the Horizontal and Vertical sync data down the green sync signal is very sensitive to impedance mismatch.

If you were to cut the Green cable 3cm shorter than the other two cables, then the impedance could become slightly lower than 75 ohms (when compared to the other two cables) causing the sync to drop or become unstable.

(This only really affects long runs; however, it is extremely important to keep all three cables the same length to help reduce this effect.