We are tracking wild animals with VHF receivers where incoming signal sounds like high pitch impulse in every 2 seconds. Distance and environment factors are impeding signal strength so I recently added one extra whip antenna to existing one on car roof (distance 0,9 m) with BNC plug-2xBNC socket.
I can say that the incoming signal improved significally as I was hearing clear signal with two antennas from distance of 700 m and no signal with one antenna and same receiver parameters.