When splitting a Comcast cable signal to multiple televisions, the signal gets degraded the farther the television and cable box from the source. Running cable through your home, over 75 feet, often requires the use of an amplifier splitter to increase the cable signal. A regular splitter only connects coaxial cables to the source, while the amplifier splitter also plugs into an electrical outlet for power.
Turn off the cable box and television before connecting or disconnecting any wires.
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Remove the cable from the "Antenna In" on the Comcast cable box.
Screw the coaxial cable from the wall into the amplifier splitter where it indicates "In" and connect other coaxial cables to "Out" jacks. Each television requires an individual coaxial cable connection.
Connect any "Out" coaxial cables to the "Antenna In" connectors on each Comcast cable box.
Leave the "Antenna Out" connection on the cable box to the "Antenna In" jack on the television. This doesn't need changing if it's already connected.
Plug in the power supply to the amplifier splitter, and then turn on the television and cable box to test your signal.