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High sensitivity portable radio direction finder










Image Number 3 for United States Patent #4475106.

A simple inexpensive, very effective high to ultra high frequency radio direction finder is disclosed utilizing two parallel antenna units with switching means for alternately connecting the antenna units to a conventional unmodified FM or NBFM receiver at an audio frequency rate. If the centroids of the antenna units are not on a line normal to the path of the monitored input signal, the amplitude of the audible tone output signal resulting from the difference in phase of the alternately received input signals at the time of switching will vary with the angle of deviation of the antennae from this normal position. The slight alternations of phase are demodulated as slight frequency changes and produce a tone in the FM receiver output having the audio frequency of the antenna switching device. When the line between the electrical centroid of the two antennae is rotated to lie normal to the path of the monitored signal as it passes a point midway between the two antennae, the receiver tone output is a null or minimal, whereas it increases in amplitude as the antenna units are rotated further from normal. The apparatus includes automatic circuitry for resolving the ambiguity of the monitored signal source fore or aft of the operator when the output is at null. This is done by providing a positive indication of which way to rotate the antennae to reach the preferred null, and includes both aural and visual output displays.








 
 
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