A T coupler is another name for a two-way splitter. These devices will allow one cable to split in two directions or two cables to come together into one output. In most cases, these devices are bi-directional, meaning that information can go both ways through the coupler. Even though a T coupler has this capability, most splitters are labeled as though they only work in one direction. The reason for this is usually in the internal setup of the device, one position is optimized for input and the other two will have unequal amounts of coupling loss.
This device gets its name from its original common shape. When these devices first came into use, they were shaped like a capitol T or Y. In fact, Y coupler is another generic name for a two-way splitter. The shape made it easy to identify and label the connections. In addition, both shapes have one leg that is different in design from the other two when viewed from any angle. This allowed users to single out one post as the main input or output of the splitter.
The most common household T coupler is used for cable television. It is very common that a home has more than one device connected to the cable system. When there are more devices than there are cables, people will commonly use what they call a cable splitter. These splitters are just a specific name for a standard T coupler.
A cable splitter is often more of the Y shape than the T shape, although a wide number of variations exist. This type of T coupler will generally have one coaxial connection on one side and two on the other; this makes it easy to see which cable is the main in and which are the outs. In addition to this design, many splitters will have numbers printed or stamped by the out connections. These numbers are typically in decibels and denote the coupling loss on each post.
Coupling loss is created when a signal moves from one circuit to another or from one medium to another. It is basically a portion of the signal that is destroyed in the transfer. Even though it is no longer a useful signal, the energy doesn’t dissipate, instead it is translated to transmission noise.
In a T coupler, the three posts are each connected to their own circuit. The input jumps from its own location to that of the two outputs. During this process, the signal is degraded by the amount listed on the coupler. This means that high numbers are bad — the signal is more degraded —, and lower numbers are better.