The above answer is correct. Only a single antena is needed, but if you have more than 1 radio requiring VOR/GS you will need 2 splitters. If you only have the SL 30 then you will run the cox directly to the SL30 and it will split the signals internally. If you ahve another radio, like a Garmin 430 you will need 2 splitters-- one to disassemble the signal so the 430 can use it, and then one to put it back together and send it to the SL30.
Vic
