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Doppler-Shift Radio Direction Finding

March 11th Fact-of-the-Day

Radio amateurs most often use the directional characteristics of antennas to find bearings to unknown signals. Doppler-shift is an alternative radio direction finding technology that doesn't require a directional antenna. There are two variations known as Doppler and Quasi-Doppler. To understand the principle underlying Doppler direction finding, visualize a vertical dipole mounted on the end of an arm that rotates rapidly around its opposite end. The received frequency of an unknown signal will increase as the dipole rotates toward the source of an unknown signal and will decrease as it rotates away. The frequency will be midway between the highest and lowest frequency extremes and the frequency will be transitioning from high to low when the arm is pointing directly at the source of the signal. ©2005 Martek International All rights reserved.


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