Portable communications devices with reduced interference between communication systems. One embodiment provides a portable communications device including a first antenna, a second antenna, a first transceiver configured to operate over a first range of frequencies, a second transceiver configured to operate over a second range of frequencies and a third range of frequencies. The portable communications device includes an isolator circuit coupling the first transceiver and the second transceiver to the first antenna and the second antenna. The isolator circuit is configured to provide isolation between the first transceiver and the second transceiver when the second transceiver is operating in the second range of frequencies. The portable communications device further includes a bidirectional diplexer coupling the second transceiver to the isolator circuit. The bidirectional diplexer is configured to reduce an electrical transmission length when the second transceiver is operating over the third range of frequencies.