As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
USING HF#1, THE HF ANTENNA WAS UNABLE TO TUNE ON MULTIPLE HF FREQUENCIES. (HF #2 WORKS NORMAL). A STEADY TONE LASTING APPROXIMATELY 10 SECONDS WOULD PRECEED OUR INABILITY TO TRANSMIT.(NO SIDE TONE) AT 3 HOURS INTO FLIGHT. WE ATTEMPTED HF#1 AGAIN AND IT WORKED NORMALLY. GROUNDED - YES. PERFORMED OP CHECK ON HF#1 IAW AMM 23-11-00. OP CHECK GOOD.