Great question I receive is how to split the signal from the antenna for two or more radios to use. If you live an area that doesn’t allow for multiple antennas to be installed, or have multiple radios that you would like to share a common antenna with, then splitting the signal is a big concern.
Signal splitting can be very easy, or quite difficult, depending on your particular needs. Many scanner listeners will usually get by with a cable tv splitter. These splitters will work with scanners, the only problem is that they are designed for 75 ohm coax cable and require F connectors. You’ll need an adapter of some sort if you want to use them for 50 ohm cable.
The only problem with using a simple splitter like this is that you can’t transmit through it. Transmitting through a signal splitter will cause damage to the other radios connected to the splitter.
An element of filtering is required if you want to use two transmitters with one antenna. Diplexers allow either one radio to use two antennas, or two radios to share one antenna. The diplexers have filters that prevent transmitted RF energy from traveling into the second radio and causing damage. Simple diplexers that split between two bands can be quite small, but as the split signal gets closer and closer, the diplexers will become larger and larger.
The easiest and safest way to share an antenna between two radios is with an A-B antenna switch. Only one radio at a time can use the antenna, but then you’re guaranteed that you won’t backfeed RF energy into the second radio.
My preference is using separate antennas for each radio, then every transmitter has their own dedicated antenna and I don’t have to worry about switching antennas, or if a radio is currently connected to a radio or not. Otherwise the A-B switch is your best choice for sharing one antenna between two radios.