Sec. 80.819  Requirements for radio direction finder.

    (a) To be approved by the Commission during an inspection the radio 
direction finding apparatus must:
    (1) Be capable of receiving signals A1A, A2B and R2B emission, on 
each frequency within the band 285-515 kHz assigned by the Radio 
Regulations for distress and direction finding and for maritime radio 
beacons, and be calibrated to take bearings on such signals from which 
the true bearing and direction may be determined; and
    (2) Possess a sensitivity, sufficient to permit the taking of 
bearings on a signal having a field strength of 50 microvolts per meter.
    (b) The calibration of the direction finder must be verified by 
check bearings or by a further calibration whenever any changes are made 
in the physical or electrical characteristics or the position of any 
antennas, and whenever any changes are made in the position of any deck 
structures which might affect the accuracy of the direction finder. In 
addition, the calibration must be verified by check bearings at yearly 
intervals. A record of the calibrations, and of the check bearings made 
of their accuracy and the accuracy of the check bearings must be kept on 
board the ship for a period of not less than 1 year.