The RCA termination connectors are to ease your adding proper isolation
between the sound card and the radio. Modem transformers make a good
isolation means, or you can use the Radio Shack 500 ohm/ 1000 ohm to 8 ohm
transformer between the sound card output and the rig.
Generally, you don't want the rig ground to end up on the sound card ground.
(Which might also be the computer ground).
One local club member makes these up with RCA plugs on plastic boxes
salvaged from Scotch electrical tape. Altoids tins are another suitable
enclosure for small transformers, and an RCA connector mounts easily to the
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