We are tracking wild animals with VHF receivers where incoming signal sounds 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 with BNC plug-2xBNC socket[![BNC plug-2xBNC socket][1]][1]. 

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.   


  [1]: https://i.sstatic.net/prAU5.jpg