What was found
UNABLE TO COMMUNICATE ON HIGH FREQUENCY. RECEPTION UNREADABLE, BOTH HIGH FREQUENCY UNUSABLE. HF DATA LINK OFF MESSAGE ILLUMINATED. AN EMERGENCY WAS DECLARED, RETURNED TO DEPARTURE, AND LANDED. THE AIRCRAFT WAS GROUNDED. REPLACED BOTH LEFT AND RIGHT HIGH FREQUENCY TRANSCEIVERS IAW MM 23-11-05. OPS CHECKED GOOD IAW MM 23-11-00.