This antenna selector circuit allows switching between two FM antennas via a logic signal.
Gates IC1b and IC1a provide switching and interface between the logical form of 5 and 12 V supply voltage, required for selection. When input A is logic state H, IC1a's output will be L and that of IC1b will be H. In this case, current will flow from the positive supply terminal to IC1a, through T2 R9 and D8; T2 lead and D9 light.
When input A is logic state L, then IC1b is L, the current flow from source to IC1b positive connector, through Q1, R7 and D7, then T1 is open and light D10. Meanwhile, the two relays connected in series, RE1 and RE2, are placed under tension, their contacts close and VHF signal appear at C input and D output