双混频时差测量系统的误差分析与试验研究

Error analysis and experiment of dual mixer time difference measurement system

双混频时差测量系统的实际测量能力与公共频率源、混频器、过零检测器和时间间隔计数器等关键部件的特性息息相关。从双混频时差测量的原理入手,分析了各关键部件对系统本底噪声的影响,并搭建了试验平台,对影响系统本底噪声性能的因素进行了试验验证。试验结果表明,双混频时差测量系统的本底噪声与公共频率源的短期稳定度正相关,而与其长期稳定度没有直接关系。同时时间间隔计数器的读数值增大也将使得公共频率源的短期稳定度的影响进一步变大,因此需要通过一个移相器使计数器读数值保持在一个较小的范围内,以保证系统的本底噪声性能。

The actual measurement capability of the dual mixer time difference measurement system is closely related to the characteristics of the common frequency source, mixer, zero crossing detector and time interval counter （TIC）. The relationship between these key components and the floor noise performance of the system have been analyzed and verified through an experimental platform. The experimental results indicate a positive correlation between the system floor noise performance and the short-term stability of the common oscillator. A large TIC reading would also worsen floor noise performance. In order to avoid a poor performance,a phase shifter is needed to keep the TIC reading varying in a small range.