Edit: I meant to quote this:
Unless you are talking about the amplified drop in charger, you can't add a VHF antenna to the G5. The top antenna is only for 7/8 and the secondary antenna (VHF or UHF) is built into the unit. So, with the unit by itself, there's no way to add a VHF antenna to it unless of course you took the unit apart and did some stuff to it. Even with the amplified drop in charger, I don't remember if the secondary band is covered on the external antenna (7/8 is the primary band).
Just an FYI.