时间：2011-03-11 23:13来源：蓝天飞行翻译 作者：admin 点击：次
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hertz. The term used for the frequency of any cyclic repetition. One hertz, Hz, is one cycle of events each second. Hertz antenna (radio antenna). An ungrounded, half-wave antenna whose resonant frequency is determined by its distributed capacity. This capacity, and therefore its resonant frequency, is determined by the antenna length. heterodyne. To mix two electrical or acoustic signals having different frequencies so they produce two new signals whose frequencies are different from either of the two original signals. If a signal with a frequency of 1,000 hertz is mixed with a signal having a frequency of 800 hertz, two new frequencies are produced: the sum of the two frequencies, 1,800 hertz, and the difference between the two, 200 hertz. heterodyne-type frequency meter. An instrument used to determine the frequency of alternating current. The frequency of an accurately calibrated internal oscillator is varied and compared with the frequency being measured. When the two frequencies are mixed, a third frequency, called the beat frequency, is produced. This beat frequency is the difference between the two. The variable frequency is changed until the beat frequency disappears. When it disappears, the frequency being measured is the same as that being produced by the oscillator. heterogeneous mixture. A physical mixture of dissimilar ingredients. Concrete is a heterogeneous mixture of sand, gravel, and portland cement. hexadecimal number system. A number system that uses 16 as its base. The values from 0 through 9 are represented by the numerals 0 through 9, and values from 10 through 15 use the letters A through F. Hexadecimal numbers can easily be converted into binary numbers for use in a computer. Values of up to decimal 255 or binary 1111 1111 can be expressed by using only two hexadecimal digits, FF. Decimal Hex Binary Decimal Hex Binary 0 0 0000 8 8 1000 1 1 0001 9 9 1001 2 2 0010 10 A 1010
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