| 摘要 |
A directional concealed object locator, say metal detector, employing a beat frequency oscillator and at least two search oscillators. The search oscillators each include a loop antenna which in part serves to determine the search frequency signal rate of each oscillator and functionally serves to produce an electromagnetic field of relatively large proportions from each loop antenna which is portably so orientable as to have the extended electromagnetic field lines, which emanate from each loop antenna, separately coupled to a buried, or otherwise obscured metal object and thereby produce changes in the search signal rate as the proximity therebetween is varied. The common beat oscillator produces a signal so related to each search frequency signal as to be conjointed in a heterodyne detector and therefrom produce at least two audio frequency notes the resultant periodicities of which are proportional to the difference between each of the search frequency signal rates and the common beat oscillator signal rate. Further improvement is provided in that each resultant audio frequency difference rate is aggrandized so as to change at a rate, in hertz, which is far in excess of any change, in hertz, directly produced in each search fundamental frequency signal by varied object proximateness. The effect is to cause an apparent increased sensitivity, which is shown in one form so as to be variable, in the operation of the metal detector, while at the same time providing proximal resolution by way of a left-hand, or else right-hand, indication of the hidden object transversal path.
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