For wireless digital communications, digital user signal is usually at first converted into analog domain and then modulated to radio frequency by one or two steps.

对于无线数字通信而言，通常将数字用户信号首先转换到模拟域中，然后通过一个或两个步骤将其调制到无线电频率。

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Multiplier is the circuit which is conformed of nonlinear elements and can make two signal multiplied so that it can implement frequency transformation.

相乘器是由非线性元件组成，可以实现两个信号的相乘，完成频率变换的电路。

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Combining two methods, it is detected and analyzed that the weak signal slowly frequency change accompanied by noise.

结合所提出的两种方法，对带噪声的频变微弱振动信号进行了检测分析。

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Power companies and networking startups have spent years touting a technology called broadband-over-power lines, or BPL. In those systems, the utility sends a data signal across existing wires at a much higher frequency than electricity, so the two signals don't interfere.

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The cylindrical speaker features two high-performance drivers, a built-in bass port and digital signal processing software to extend frequency response on the high end while providing tighter low ends for deeper bass response.

ENGADGET: JBL freshens its portable speakers with Micro II, Bluetooth-toting Flip and Micro Wireless