Depends on the radio. Some have regular antenna ports so an external antenna switch is not required. If it is designated as a separate RX antenna port, they usually have a different RF connector such as an RCA type but not necessarily, then it is indeed for RX only. It goes directly to the RX section and is not switched to the TX section at all. My Icom IC-735 had one with RCA connectors. Normally there was a jumper connecting it to the main antenna jack. Pulling the jumper and inserting rx filters allowed me to use the filters without worrying about them being subjected to RF when I transmitted.
Ah!
Upon further investigation, I see my Kenwood has two SO239 connectors for use with two HF antennas and a RCA port for a receive antenna. A RCA male/SO239 adapter is all that's needed if using coax. My 590SG has a enable/disable RX antenna button on the front.
Nothing else needed.
Except a nice receive antenna.
Thanks again.
By the way, I love WWDX's new look and features after the upgrade.