Direction Finding System using Pseudo Doppler Method is realized in the frequency of 20MHz-100MHz. Commercially available r.f. receiver is used to tune for he desired frequency and better sensitivity. Other parts including the antenna switching circuits are designed and fabricated. This system shows that the direction finding is possible with the r.m.s. direction error less than 5℃. The error sources include the antenna position error, the switching time of the pin diode, variation in the gain and d.c. offset of the commutative filter, and the signal to noise ratio. These factors are analyzed and the gain and d.c. offset of the commutative filter is shown to be the major source of the direction error. If the gain variation of 5% and d.c. offset of 50mV are assumed, then the maximum direction errors of 4.1, 5.7℃, and 6.9 are found depending on the total number of antennas, 3, 4 and 8, respectively.
