Signal Splitters for Digital Television and HDTV
Anyone that has attempted to connect televisions with coaxial is familiar with the signal splitter or simply “splitter.” The signal splitter accepts a coaxial cable input and divides the signal energy “N” number of ways through output ports. Splitters outputs range from 2 to as many as 8. Since signal energy at the input is divided among the number of outputs, the signal at the output ports of a 2-port splitter is greater than the signal available from the output ports of an 8-port splitter. Therefore, an 8-way splitter has greater loss (signal attenuation) than a 2-way splitter.
High quality splitters specify the signal attenuation of the input signal at any one of the output ports. In an 8-way splitter for example, signal attenuation is 10.4 dB or in other words, signal applied at the input of an 8-way splitter is attenuated 10.4 dB at the output ports. Depending upon where this splitter is added in the signal chain, 10.4 dB of signal attenuation may or may not be an issue.
Not all splitters are created equal. This is clearly evident to technicians that install and service cable/antenna systems. Low quality splitters lack the mechanical integrity for today’s antenna and cable systems. Digital television and HDTV require high quality splitters for reliable transport of signals. Splitters must be mechanically and electrically “sealed” to maintain the quality of the signals passing through them. A good mechanical seal at the body of the splitter prevents moisture from entering the enclosure and corrupting the internal components. A good mechanical seal generally implies a good electrical seal. Poor quality splitters can “leak” signal energy into the atmosphere and “radiate” electrical magnetic interference (EMI). This is undesirable as what tends to radiate out of a device also can be received by the device. A splitter that radiates signal energy from poor shielding can receive interference that corrupts signals passing through the splitter.
Well machined, cast metal splitters provide over 100 dB of protection (isolation) from generating and receiving interfering signals. High quality splitters also have well-machined “F” port threads. It is very frustrating attempting to thread an “F” connector on poorly machined F-ports. Finely machined, F-port threads and a smooth, seating-surface for connector contact work together to maintain the best signal transfer from the cable through the splitter.
High quality splitters can be used indoors and outdoors. When using splitters outdoors, the connectors should be weather-proofed at the face of the splitter. Indoors, splitters can be mounted anywhere. Signal splitters are passive devices, meaning that they do not contain internal components require an external source of power for operation. Therefore splitters can be installed in basements, crawl spaces, and attics. Anywhere cables must share a common input, splitters can be installed.
If you are installing a media distribution panel, high quality splitters will mount in the hole-patterns of name-brand media enclosures. This is a particularly advantageous because the best high-isolation (130 dB EMI) splitters are required to prevent interference from occurring between closely spaced cable connections within the enclosure. The media enclosure can be populated with high-quality signal splitters in the desired configuration.
So, you would like to use a splitter but are not sure if you can add a 2-way, 4-way, perhaps an 8-way device without degrading the digital television signal? If you don’t have a signal level meter for making digital signal measurements, use the DTV tuner’s signal indicator and monitor the effect of the splitter’s attenuation as the device is added to the signal chain. If the attenuation is too great, the signal indicator will likely register within the “poor” range. The HDTV video may also freeze or “tile” in which case you would have to either remove the splitter or select a device with fewer output ports.
Steve Zahn, Doc. #122605
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