If you plan it correctly, you can mount your 1400 indoors and run the antenna cable outside and up the tower. This shouldn't be done for long links, and it will drop your signal strength at the antenna.
Other than that, Cisco does not have such a bridge. Your only option would be to mount a 1242 in a NEMA-enclosure on top of the tower.
Keep in mind that Cisco and other cable makers have a dual-strand coax, so it's still one cable you're running.