The low frequency exhaust noise of a diesel(4 85), its generation, frequency characteristics and influencing factors have been studied through theoretic calculation, analysis and experiment.
针对柴油机（4 85 ）低频排气噪声，对其产生机理、规律及其影响因素等作了理论计算、分析及实验。
2
A design method for low phase noise agile X-band frequency synthesizer is presented, the theoretic analysis and calculation is performed and the test results are given.
介绍一种低相噪、捷变频x波段频率综合器设计方法，并进行理论分析、计算，最后给出测试结果。
3
So, it has very wide applied fields and very important theoretic meaning to study, design and develop audio-frequency measurement technique to measure audio-frequency electric parameters.