航空術(shù)語(yǔ)詞典Dictionary of Aeronautical Terms 中

時(shí)間：2011-03-11 23:13來(lái)源：藍(lán)天飛行翻譯 作者：admin 點(diǎn)擊：次

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
3 3 0011 11 B 1011
4 4 0100 12 C 1100
5 5 0101 13 D 1101
6 6 0110 14 E 1110
7 7 0111 15 F 1111
hexagon. A closed, plane figure that has six sides.

hexagon head bolt. A bolt whose head has six sides (a hexagon). A hex-head bolt can be turned with an open-end wrench or with either a six-point or a 12-point socket wrench. The six flat sides of a hex-head bolt allow the wrench to be repositioned more often than could be done with a square-head bolt, and this makes for easier installation and removal.
hexode (electron tube). A form of electron tube having six active electrodes. The electrodes are the cathode, the anode, the control grid, and three other grids that serve special functions in controlling the passage of electrons between the cathode and the anode.

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