I would like to run two VHF radios into a single antenna in my vehicle.
Are you wanting to have two VHF radios that transmit from the same antenna? If so, then there's no easy answer. You'll need an antenna relay that cuts out the feed to one radio when the other is transmitting. Otherwise the transmitting radio will seriously overload the receiver of the other radio. If the frequencies are far enough apart, you could use pass-reject style of cavity duplexer like is used on repeaters, but they typically have very sharp tuning, so you'd lose the frequency agility of your radios. Oh, cavity duplexers for VHF are pretty big. A single cavity is typically about 4 inches in diameter and about 24 inches long. Also, again if your frequencies are far enough apart, there's a company in Canada called DCI (
http://www.dci.ca/) that makes some nice RFI filters that might be sharp enough to block one radio from getting into the other.
If both radios are receive-only, a multicoupler would work. Some of the scanner dealers sell the Stridesberg (sp?) multicoupler. You could also do it on the cheap with a cable TV splitter.