If the antennas are for different bands, you want a Diplexer or Triplexer depending on your exact application.Is there a way I can connect multiple antennas to one run of LMR400 coax?
Assuming you are going to use the antenna for different bands, other responses will address that telling you about using diplexers to do that. If you are trying to use it for receiving and transmitting on a single band,, Ubbe's response about duplexers addresses that. But if you are thinking you can use more than one antenna to improve reception on one band, you have a can of worms. This is because the phase of the signals are as likely to weaken your signal as they are to strengthen it unless the spacing of the antennas and signal direction is addressed for that frequency---you really do not want to go there.Is there a way I can connect multiple antennas to one run of LMR400 coax?
Expensive solution: https://www.tessco.com/product/diplexer-public-safety-cell-80-520-694-270050w-120-296433A diamond discone and a 700-900 MHz yagi
A little better price here: ($59.95)