As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HF2 WAS TESTED IN FLIGHT BETWEEN KSLC AND KSEA ON FREQUENCIES 8843 AND 5547. FLIGHT CREW WAS UNABLE TO VERIFY POSITIVE VOICE COMMUNICATION ON HF2. SUCCESSFUL VOICE COMMUNICATION WAS COMPLETED ON HF1. GROUNDED - YES. REMOVED AND REPLACED #2 HF COUPLER PER B737-800 AMM 23-11-61 & #2 HF TRANSCEIVER IAW AMM 23-11-21.