In plain language: A sound-card interface couples computer audio to a radio’s receive and transmit audio paths and may also provide isolation and a PTT circuit.
Why the station behaves this way
Its job is level control and signal routing, not automatic mode selection or guaranteed galvanic isolation. Internal and external interfaces vary widely.
A common wrong turn
A USB connector on an interface does not prove that the radio audio path, PTT polarity, cable wiring, or software device selection is correct.
What to do at the radio
Match the interface cable to the exact radio, select input and output devices explicitly, start levels low, verify isolation and PTT behavior, and inspect the transmitted spectrum.
Operating boundary
Use current equipment instructions, legal operating limits, the exact signal path, and observed conditions. A connector, software label, transformer ratio, or forecast value does not prove complete-system performance.
