Many Kenwood transceivers have a separate RX only input labeled 'HF RX ANT' , which is mainly and RCA female connector, that goes the the rig's RX / TX internal relay switching. Kind of sucks that it doesn't work past 30MHz, like for 6M. Oh BTW, not just Kenwoods, but my older Icom IC-745 transceiver has this RCA jacked loop-around connection, where unplugging that, and having only your receive-only antenna, plugged into that, works just the same.