that splitter above is for TV signals. It lets you connect 1 antenna to 2 TVs. TVs are PASSIVE receiving devices, which is why this is OK.
If you connect two radios via a splitter and transmit using one of them then that power is being forced into the front end of the other radio, and will quite possibly damage it. I recommend you talk to someone who knows radios better, I doubt it's a good idea to have a setup like that.
The splitters whitworths have are for using your VHF antenna for AM/FM reception, they have a choke/RF filter in them to stop RF power being fed into your AM/FM radio which is why you can use them without damaging the AM/FM radio.