共查询到20条相似文献，搜索用时 671 毫秒
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采用2片555时基电路，其中一片控制频率，另一片控制占空比．产生频率为30Hz～10MHz连续可调；在10MHz频带宽度内，占空比为1％～99％连续可调的矩形触发脉冲，且频率和占空比均可独立调节． 相似文献
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黄四南 《衡阳师范学院学报》2004,25(6):37-39
基于MC13175／13176的无线电发射电路工作频率范围为260～470MHz，902～928MHz，可以作为FM／AM通信系统中的发射器，发射功率可调至10db，功率输出采用差分形式，可以使用环形天线或者平衡和不平衡变压器输出。电源电压1．8～5V，待机模式电流10μA。 相似文献
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A wideband cavity-backed slot antenna operated in the ultra-high frequency(UHF)band is introduced.The antenna has a compact structure and low profile with the size ratio of the ground plane to the slot only 1.6:1.The measured impedance bandwidth of VSWR≤3 achieves 85.3%,covering a frequency range from 390 MHz to 970 MHz.The measured gain is about 5.5～7.5 dB. 相似文献
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介绍L波段宽带线性功率放大组件的设计与制作，该组件在工作频率600～970MHz范围内，输出功率≥20W，增益≥43dB，三阶互调≤-30dBc，输入输出驻波比≤1.5：1。 相似文献
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宋跃 《湘潭师范学院学报(社会科学版)》2000,21(3):61-64
对频率为1Hz～10MHz的稳定信号，在保证1／1000的测试精度下，用8098单片机完成其频率或周期的最优测试方法，讨论其测试的硬软件设计、误差分析、测试范围分析以及为提高测试速度或测试精密度时N的最优值确定。 相似文献
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设计了一种多分支平面印刷天线,采用微带线馈电方式,其中微带线设计成T形,与辐射单元匹配.辐射单元由3个L形的金属面结构构成,其分别工作在2.4 GHz、3.5 GHz和5.4 GHz,可应用于无线局域网（WLAN）和全球微波互联接（WiMAX）系统.通过电磁仿真软件HFSS对这种天线进行设计,在WLAN应用频段上10 dB阻抗带宽分别为1 GHz （4.9～5.9 GHz）和310 MHz （2.24～2.55 GHz）;在WiMAX应用频段上10 dB阻抗带宽380 MHz （3.3～3.68 GHz）.实测结果表明,这种天线具有良好的远场辐射特性,其增益在2.5～4.7 dBi之间. 相似文献
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基于DDS技术的高速等效采样示波器设计 总被引：1，自引：0，他引：1
为了更好地实现对高频周期信号的采样,设计了基于DDS技术高速等效采样的数字示波器,以不大于1 MHz的实时采样率实现了最高2.5 GHz的等效采样率。系统电路以CycloneIII FPGA芯片为核心,结合外围器件,完成了测量频率范围10 Hz～15 MHz,输入信号范围2 mV～16 V,水平显示分辨率25点/div,垂直灵敏度包括2 V/div、2 mV/div共10档可调,实时采样与等效采样相结合的数字存储示波器。本设计电路结构简单,以低速AD实现了高速信号的采集,实现方案新颖。 相似文献
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在众多的传播媒体中,有线电视依其独特的优势迅速发展起来,然而,许多院校中,正在运行的系统大都还是80年代末、90年代初建立的有线电视系统,其稳定性能差,频道资源短缺,线路老化,已难以保证良好的图像传输质量,亟需升级换代。一、现状闭路电视,共用天线闭路电视,一举发展到300MHz、450MHz、550MHz甚至800MHz邻频传输的有线电视。具有双向功能的交互式有线电视在发达国家已开始应用,我国也开始起步,有线电视最终将与信息高速公路接轨。也许有一天,人们打开电视,接收到的不是几个、几十个,而是几百个电视节目。现在,绝大多数单位还停留在共用天线闭路电视阶段,其现状: 相似文献
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《西安文理学院学报》2020,(3)
根据GPS的L_2(1 227 MHz±10.23 MHz)和L_5(1 176 MHz±12 MHz)两个工作频带相邻的特性,设计了一个可以覆盖这两个频带的宽频带圆极化天线.该天线采用空气作为介质,利用探针进行馈电,并设计了一种宽频带90°移相功分网络.所设计的天线经过仿真优化后,加工实物并测试,实测天线驻波带宽26%,轴比小于2.2 dB,增益大于4.8 dBi.实测结果与仿真结果吻合良好,达到天线技术指标要求. 相似文献
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邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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YANGShiguo 《重庆大学学报(英文版)》2004,3(1):86-88
The problem on the geometrc inequalities involving an n-dimensional simplex and its inscribed simplex is studied. Aninequality is established, which reveals that the difference between the squared circumradius of the n-dimensional simplex andthe squared distance between its circumcenter and barycenter times the squared circumradius of its inscribed simplex is not lessthan the 2(n-1)th power of n times its squared inradius, and is equal to when the simplex is regular and its inscribed siplex is atangent point one. Deduction from this inequality reaches a generalization of n-dimensional Euler inequality indicating that thecircumradius of the simplex is not less than the n-fold inradius. Another inequality is derived to present the relationship betweenthe circumradius of the n-dimensional simplex and the circumradius and inradius of its pedal simplex. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献
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GUO Bao-feng Xiao Da-wei 《重庆大学学报(英文版)》2005,4(3):129-133
Using virtual reality for interactive design gives a designer an intuitive vision of a design and allows the designer to achieve a viable, optimal solution in a timely manner. The article discusses the process of making the Virtual Reality System of the Humble Administrator＇s Garden. Translating building data to the Virtual Reality Modeling Language （VRML） is by far unsatisfactory. This creates a challenge for computer designers to do optimization to meet requirements. Five different approaches to optimize models have been presented in this paper. The other methods are to optimize VRML and to reduce the file size. This is done by keeping polygon counts to a minimum and by applying such techniques as object culling and level-ofdetail switching. 相似文献