It it really useful to terminate unused 75Ω outputs on a coax splitter?

2018-10-12 01:17:57

When discussing improvements to my home HDTV Antenna/distribution system a colleague brought up the need to terminate all coax, even unused splitter ports.

My understanding of the way terminator works is that they prevent wave reflection, which can cause ghosting in analog signals and in my case - digital HDTV - noise. However for the reflection to introduce noise I assume you need some cable length, so that the reflected signal is actually offset from the main one.

In the case of a splitter the length is very short - limited to the splitter's own wiring. Would that still be enough to cause noise? If not, could it even have the inverse effect of preventing an in-phase reflection from actually boosting the signal's strength to used ports?

Lack of termination is a particular case of impedance mismatch. An impedance mismatch on one port of a power divider ("coax splitter") means that the common port of the divider itself will not present the the intended impedance to

  • Lack of termination is a particular case of impedance mismatch. An impedance mismatch on one port of a power divider ("coax splitter") means that the common port of the divider itself will not present the the intended impedance to the incoming signal.

    (From a circuit analysis perspective, this is the same thing as a lumped-component network of some sort that has the wrong impedance on its ports for the pair of transmission lines attached to it. No lengths of unterminated line are necessary.)

    This mismatch will cause reflections which propagate backwards along the line. What happens after that depends on the electrical characteristics of the next thing-that-is-not-a-transmission-line the reflection hits, but a simple case is if there is another similar mismatch in the line, which will produce the second (forward) reflection called ghosting, the time between reflection depending on the length of line between those two defects.

    2018-10-12 03:27:35