What Is an A/B Switch?

Front of A/B Switch
Front of A/B Switch, RadioShack Model 15-1217. Image property of Matthew Torres, tv.about.com
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An A/B switch is a very useful television accessory that allows two RF (radio frequency)/coaxial devices to connect to a single RF/coaxial input. It allows you to toggle between the two separate coaxial signals on a single viewing display. With RF inputs rather than the three color-coded inputs of RCAs, it connects to a 75-Ohm cable.

A/B switches vary in style; some have simple, metallic casings, while others are plastic with remote control capabilities.

How Are A/B Switches Used?

Here are three common scenarios in which you might use an A/B switch:

  1. You own an HDTV, subscribe to analog cable, and use an antenna. Since most HDTVs have a single RF input, you’d need an A/B switch to connect the analog cable and antenna to the RF input on the HDTV. The result would be the ability to toggle between the two RF signals without disconnecting cables.
  2. You own an analog DTV and use a DTV converter, antenna, and VCR. You want to continue to watch TV on one channel while the VCR records on another. Given that the DTV converter controls the incoming signal to the VCR, you’d actually need two accessories to make this happen: an A/B switch and a splitter. Connect the antenna to the splitter, which splits a single input into two outputs. The two cables go on separate paths until reunited at the A/B switch. Read more about this scenario.
  3. You want to monitor two camera feeds on a single viewing display. The camera's output is RF, so you need a coaxial cable. The viewing display has only one coaxial input. Connect each camera to the A/B switch so you could toggle between the first camera and the second.