关于POE系统，说法正确的有（）。
A: APOE系统包含PSE设备和PD设备两部分，其中PD为供电设备，PSE为受电设备
B: BPOE通常采用min-span和end-span两种供电方法
C: C通常PSE可以支持mid-span和end-span两种方法，PD只能支持一种
D: DPOE电源提供的电压为48V，输出功率不超过13W
A: APOE系统包含PSE设备和PD设备两部分，其中PD为供电设备，PSE为受电设备
B: BPOE通常采用min-span和end-span两种供电方法
C: C通常PSE可以支持mid-span和end-span两种方法，PD只能支持一种
D: DPOE电源提供的电压为48V，输出功率不超过13W
B,C
举一反三
- 关于POE系统，说法正确的有（）。 A: POE系统包含PSE设备和PD设备两部分，其中PD为供电设备，PSE为受电设备 B: POE通常采用min-span和end-span两种供电方法 C: 通常PSE可以支持mid-span和end-span两种方法，PD只能支持一种 D: POE电源提供的电压为48V，输出功率不超过13W
- 关于POE系统，说法正确的是（） A: POE系统包含PSE设备和PD设备两部分，其中PD为供电设备，PSE为受电设备 B: POE通常采用mid-span和end-span两种供电方法 C: 通常PSE可以支持mid-span和end-span两种方法，PD只能支持一种 D: POE电源提供的电压为48V，输出功率通常不超过13W
- 关于PoE供电技术，下列说法中正确的是（）。 A: POE交换机连接POE受电设备时，通常都是按交换机的最大输出功率给设备供电的 B: POE供电器和分离器是通过网线的1236口供电的 C: POE交换机可以跨设备连接AP面板为其供电 D: POE交换机可以通过网线的1236口同时实现供电和传输数据信号
- 关于PoE供电技术，下列说法中正确的是（）。 A: POE交换机连接POE受电设备时，通常都是按交换机的最大输出功率给设备供电的 B: POE供电器和分离器是通过网线的4578口供电的 C: POE交换机可以跨设备连接AP面板为其供电 D: POE交换机可以通过网线的1236口同时实现供电和传输数据信号
- 1</span>、</span></span>δ</span></span>(n)</span>的</span></span>z</span>变换是</span></span></u>。</span></span></u></p>1B.</span>δ</span></span>(w)C.2</span>πδ</span></span>(w)D.2</span>π</span></span></span></li></ol>2</span>、从奈奎斯特采样定理得出，要使实信号采样后能够不失真还原，采样频率</span></span>fs</sub></span>与信号最高频率</span></span>fmax</sub></span>关系为：</span></span></u>。</span></span></u></span></p>A.fs</sub></span>≥</span></span>2fmax</sub>B.fs</sub></span>≤</span></span>2fmax</sub>C.fs</sub></span>≥</span></span>fmax</sub>D.fs</sub></span>≤</span></span>fmax</sub></span></span></p>3</span>、用双线性变法进行</span></span>IIR</span>数字滤波器的设计，从</span></span>s</span>平面向</span></span>z</span>平面转换的关系为</span></span>s=</u></span>。</span></span></span></p>A.</span></span>B.</span></span>s</sub>C.</span></span>D.</span></span></span></span></p>4</span>、序列</span></span>x1</sub></span>（</span></span>n</span>）的长度为</span></span>4</span>，序列</span></span>x2</sub></span>（</span></span>n</span>）的长度为</span></span>3</span>，则它们线性卷积的长度是</span></span></u>，</span></span>5</span>点圆周卷积的长度是</span></span></u>。</span></span></span></p>A.5,5B.6,5C.6,6D.7,5</span></span></p>5</span>、无限长单位冲激响应（</span></span>IIR</span>）滤波器的结构是</span></span></u>型的。</span></span></span></p>A.</span>非递归</span></span>B.</span>反馈</span></span>C.</span>递归</span></span>D.</span>不确定</span></span></span></p>6</span>、若数字滤波器的单位脉冲响应</span></span>h</span>（</span></span>n</span>）是对称的，长度为</span></span>N</span>，则它的对称中心是</span></span></u>。</span></span></span></p>A.N/2B.</span>（</span></span>N-1</span>）</span></span>/2C.</span>（</span></span>N/2</span>）</span></span>-1D.</span>不确定</span></span></span></p>7</span></span>、若正弦序列x(n)=sin(30nπ/120)是周期的,则周期是N=</u>。</span></span></span></p>A.2</span>π</span></span>B.4</span>π</span></span>C.2D.8</span></span></p>8</span>、一</span></span>LTI</span>系统，输入为</span></span>x</span>（</span></span>n</span>）时，输出为</span></span>y</span>（</span></span>n</span>）</span></span>；则输入为</span></span>2x</span>（</span></span>n</span>）时，输出为</span></span></u></span>；输入为</span></span>x</span>（</span></span>n-3</span>）时，输出为</span></span></u></span>。</span></span></span></p>2y</span>（</span></span>n</span>），</span></span>y</span>（</span></span>n-3</span>）</span></span>B.2y</span>（</span></span>n</span>），</span></span>y</span>（</span></span>n+3</span>）</span></span>C.y</span>（</span></span>n</span>），</span></span>y</span>（</span></span>n-3</span>）</span></span></span></li></ol>D.y</span>（</span></span>n</span>），</span></span>y</span>（</span></span>n+3</span>）</span></span></span></p>9</span></span>、用窗函数法设计FIR数字滤波器时，加矩形窗时所设计出的滤波器，其过渡带比加三角窗时</u>，阻带衰减比加三角窗时</u>。</span></span></span></p>A.</span>窄，小</span></span>B.</span>宽，小</span></span>C.</span>宽，大</span></span>D.</span>窄，大</span></span></span></p>10</span></span>、</span></span>在</span></span>N=32</span>的基</span></span>2</span>时间抽取法</span></span>FFT</span>运算流图中，从</span></span>x(n)</span>到</span></span>X(k)</span>需</span></span></u>级蝶形运算</span></span></span></p>过程。</span></span></span></p>A.4B.5C.6D.3</span></span></p>11</span></span>．X(n)=u(n)的偶对称部分为（）。</span></span></span></p>．1/2+δ(n)/2B.1+δ(n)C.2δ(n)D.u(n)-δ(n)</span></span></span></li></ol>12.</span></span>下列关系正确的为（）。</span></span></span></p>A</span></span>．</span></span>B.</span></span></span></span></span></p>C</span></span>．</span></span>D.</span></span></span></span></span></p>13</span></span>．下面描述中最适合离散傅立叶变换DFT的是（）A．时域为离散序列，频域也为离散序列B．时域为离散有限长序列，频域也为离散有限长序列C．时域为离散无限长序列，频域为连续周期信号D．时域为离散周期序列，频域也为离散周期序列</span></span></span></p>14</span></span>．脉冲响应不变法（）A．无混频，线性频率关系B．有混频，线性频率关系C．无混频，非线性频率关系D．有混频，非线性频率关系</span></span></span></p>15</span></span>．双线性变换法（）A．无混频，线性频率关系B．有混频，线性频率关系C．无混频，非线性频率关系D．有混频，非线性频率关系</span></span></span></p>16</span></span>．对于序列的傅立叶变换而言,其信号的特点是（）A．时域连续非周期，频域连续非周期B．时域离散周期，频域连续非周期C．时域离散非周期，频域连续非周期D．时域离散非周期，频域连续周期</span></span></span></p>17</span></span>．设系统的单位抽样响应为h(n)，则系统因果的充要条件为（）A．当n>0时，h(n)=0B．当n>0时，h(n)≠0C．当n<0时，h(n)=0D．当n<0时，h(n)≠0</span></span></span></p>18.</span></span></span>若一模拟信号为带限，且对其抽样满足奈奎斯特条件，则只要将抽样信号通过</span></span>()</span></span></span>即可完全不失真恢复原信号。</span></span></span></p>A.</span></span></span>理想低通滤波器</span></span>B.</span></span></span>理想高通滤波器</span></span></span></p>C.</span></span></span>理想带通滤波器</span></span>D.</span></span></span>理想带阻滤波器</span></span></span></p>19.</span></span></span>若一线性移不变系统当输入为</span></span>x(n)=δ(n)</span></span></span>时输出为</span></span>y(n)=R3</sub>(n)</span></span></span>，则当输入为</span></span>u(n)-u(n-2)</span></span></span>时输出为</span></span>()</span></span></span>。</span></span></span></p>3</sub>(n)B.R2</sub>(n)</span></span></span></span></li>3</sub>(n)+R3</sub>(n-1)D.R2</sub>(n)+R2</sub>(n-1)</span></span></span></span></li></ol>20.</span></span></span>下列哪一个单位抽样响应所表示的系统不是因果系统</span></span>?()</span></span></span></span></p>A.h(n)=δ(n)B.h(n)=u(n)</span></span></span></span></li>C.h(n)=u(n)-u(n-1)D.h(n)=u(n)-u(n+1)</span></span></span></span></li></ol>21.</span></span></span>一个线性移不变系统稳定的充分必要条件是其系统函数的收敛域包括</span></span>()</span></span></span>。</span></span></span></p>A.</span></span></span>单位圆</span></span>B.</span></span></span>原点</span></span></span></p>C.</span></span></span>实轴</span></span>D.</span></span></span>虚轴</span></span></span></p>22.</span></span></span>已知序列</span></span>Z</span></span></span>变换的收敛域为｜</span></span>z</span></span></span>｜</span></span><1</span></span></span>，则该序列为</span></span>()</span></span></span>。</span></span></span></p>A.</span></span></span>有限长序列</span></span>B.</span></span></span>无限长右边序列</span></span></span></p>C.</span></span></span>无限长左边序列</span></span>D.</span></span></span>无限长双边序列</span></span></span></p>23.</span></span></span>实序列的傅里叶变换必是</span></span>()</span></span></span>。</span></span></span></p>A.</span></span></span>共轭对称函数</span></span>B.</span></span></span>共轭反对称函数</span></span></span></p>C.</span></span></span>奇函数</span></span>D.</span></span></span>偶函数</span></span></span></p>24.</span></span></span>若序列的长度为</span></span>M</span></span></span>，要能够由频域抽样信号</span></span>X(k)</span></span></span>恢复原序列，而不发生时域混叠现象，则频域抽样点数</span></span>N</span></span></span>需满足的条件是</span></span>()</span></span></span>。</span></span></span></p>A.N≥MB.N≤M</span></span></span></span></p>C.N≤2MD.N≥2M</span></span></span></span></p>25.</span></span></span>用按时间抽取</span></span>FFT</span></span></span>计算</span></span>N</span></span></span>点</span></span>DFT</span></span></span>所需的复数乘法次数与</span></span>()</span></span></span>成正比。</span></span></span></p>A.NB.N2</sup></span></span></span></span></p>C.N3</sup>D.Nlog2</sub>N</span></span></span></span></p>26.</span></span></span>以下对双线性变换的描述中不正确的是</span></span>()</span></span></span>。</span></span></span></p>A.</span></span></span>双线性变换是一种非线性变换</span></span></span></p>B.</span></span></span>双线性变换可以用来进行数字频率与模拟频率间的变换</span></span></span></p>C.</span></span></span>双线性变换把</span></span>s</span></span></span>平面的左半平面单值映射到</span></span>z</span></span></span>平面的单位圆内</span></span></span></p>D.</span></span></span>以上说法都不对</span></span></span></p>27.</span></span></span>以下对</span></span>FIR</span></span></span>和</span></span>IIR</span></span></span>滤波器特性的论述中不正确的是</span></span>()</span></span></span>。</span></span></span></p>A.FIR</span></span></span>滤波器主要采用递归结构</span></span></span></p>B.IIR</span></span></span>滤波器不易做到线性相位</span></span></span></p>C.FIR</span></span></span>滤波器总是稳定的</span></span></span></p>D.IIR滤波器主要用来设计规格化的频率特性为分段常数的标准滤波器</span></p>28</span>、设系统的单位抽样响应为</span></span>h(n)=</span>δ</span></span>(n-1)+</span>δ</span></span>(n+1)</span>，其频率响应为（</span></span>）</span></span></span></p>A</span>．</span></span>H(ej</sup></span>ω</span></span></sup>)=2cos</span>ω</span></span>B.H(ej</sup></span>ω</span></span></sup>)=2sin</span>ω</span></span>C.H(ej</sup></span>ω</span></span></sup>)=cos</span>ω</span></span>D.H(ej</sup></span>ω</span></span></sup>)=sin</span>ω</span></span></span></p>29.</span></span>若x(n)为实序列，</b>X(ej</sup>ω</sup>)是其离散时间傅立叶变换，则（）</span></span></span></p>A</span></span>．X(ej</sup>ω</sup>)的幅度合幅角都是ω的偶函数</span></span></span></p>B</span></span>．X(ej</sup>ω</sup>)的幅度是ω的奇函数，幅角是ω的偶函数</span></span></span></p>C</span></span>．X(ej</sup>ω</sup>)的幅度是ω的偶函数，幅角是ω的奇函数</span></span></span></p>D</span></span>．X(ej</sup>ω</sup>)的幅度合幅角都是ω的奇函数</span></span></span></p>30.</span>计算两个Ｎ１点和Ｎ2点序列的线性卷积，其中Ｎ１>Ｎ２，至少要做()点的ＤＦＴ。</span></p>A.</span>Ｎ１B.Ｎ１+Ｎ２-１C.Ｎ１+Ｎ２+１D.N2</span></p>
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