Three different types of VLF direction-finding techniques (goniometer, tracker, and University of Tokyo type) were tested by using whistle mode VLF signals from Siple. The tests were carried out by simulating each type of direction finder (DF) in a digital computer. The results are as follows (1) the difference between the azimuth angle obtained by the tracker DF and that obtained by the University of Tokyo type DF is smaller than the difference between the azimuths given by the goniometer and by the University of Tokyo type DF; and (2) in some periods all three DF techniques give nearly equal azimuth angles, and the wave polarization agrees with that expected from the full wave calculations, but in other periods all three techniques give considerably different azimuth angles, and the wave polarizations do not agree with the theoretical ones.