Here's a quick initial sketch of the modification I'm planning to do to the original circuit (didn't add components values, refer to the original schematic)
![Remote antenna switch (4 antennas, no additional control cable) 1037904-0](https://www.eevblog.com/forum/index.php?action=dlattach;topic=248876.0;attach=1037906;image)
the modification allows to use the unit in default mode (with both switches open) or to allow for different modes of operation; by closing SW1 (and connecting the PTT circuit), the TX antenna will always be the #0 since when the PTT powers the relay, the latter will cut-off power from the remote unit so selecting antenna port #0, while in RX one will be able to use any of the four antennas.
By closing SW2, the separate TX/RX port feature will be enabled so that it will be possible to use a separate receiver, the "RX mute" contacts could then be used to "mute" the receiver when transmitting.
I believe that with such a simple mods the switch could become even more flexible; another mod, if desired, could be picking up the relay power at the remote unit and use it (with a little bit of circuitry) to power a remote active antenna or RF preamplifier, such an option could only be used with SW1 closed and PTT connected, in such a case antennas #1, #2 and #3 will be RX only ones, while the #0 will be the one used for TX (and, if selected, RX)