排序方式: 共有16条查询结果,搜索用时 15 毫秒
11.
Andrew G. Dempster 《GPS Solutions》2008,12(3):179-185
Comb filters can be designed by replacing single delays in digital filters by multiple delays. These filters are “periodic”
in the sense that their frequency response repeats itself at fixed intervals. They are thus well suited to a signal such as
GPS L1 which has a spectrum made up of lines separated by the code repetition frequency of 1 kHz. In this paper we examine
how periodic filters can be used in a conventional GPS L1 receiver. We find that comb filters assist with acquisition of weak
signals, and can improve code-tracking performance. 相似文献
12.
On arrangement of source and receivers in SASW testing 总被引:1,自引:0,他引:1
Longzhu Chen Jinying Zhu Xishui Yan Chunyu Song 《Soil Dynamics and Earthquake Engineering》2004,24(5):389-396
This study investigates the effects of source and receivers arrangement on the Rayleigh wave dispersion curve in SASW testing. Analytical studies and numerical simulations with coupled finite and infinite elements are presented in this paper. It is shown that arrangement of source and receivers has a significant effect on test results, especially for soils with high Poisson's ratio or saturated soils. Larger source-to-receiver distance and receiver spacing usually give better results, and it is unnecessary to keep them equal. To satisfy the error control requirement in Rayleigh wave phase velocity measurement, source-to-receiver distance and receiver spacing should meet corresponding minimum values, which are proposed for different Poisson's ratios of soil in this paper. 相似文献
13.
14.
在可控源音频大地电磁法野外作业中,源和勘探区间的距离可达几公里,为了了解源和勘探区间的异常体对勘探区内异常响应的影响,我们用三维压缩积分方程法做了数值模拟研究.首先对勘探区目标体进行了数值模拟,发现在高频时,观测到的异常中心位于目标体的正上方,随着频率降低,出现异常中心向远离源的方向略有移动的现象,所以对三维异常体最好用3D软件来解释.然后,对源和勘探区间存在三维异常体的情况进行了数值模拟与分析讨论.模拟结果表明只有当三维异常体达到较大的规模时,才会对目标体上方的观测曲线造成影响,否则其电阻率的变化及埋深的变化对观测曲线的影响较小,可以忽略.当异常体在源方向有延伸时,观测曲线受到的干扰最大,沿垂直源布设的方向延伸时引起的干扰中等,垂直地面向下延伸引起的干扰最小. 相似文献
15.
16.
The mitigation of radio frequency interference (RFI) has a fundamental role in global navigation satellite system (GNSS) applications,
especially when a high level of availability is required. Several electromagnetic sources, in fact, might degrade the performance
of the global positioning system (GPS) and Galileo receivers, and their effects can be either in-band (i.e., secondary harmonics
generated by transmitters of other communication systems due to non-linearity distortions) or out-of-band (i.e., strong signals
that occupy frequency bandwidths very close to GNSS bands). We investigated the effects of real out-of-band signals on GNSS
receivers and analyzed the impact on the overall receiver chain in order to evaluate the impact of the interference source.
In particular, the analysis focuses on the spectrum at the front-end output, on the automatic gain control (AGC) behavior,
as well as on the digital processing stages (signal acquisition and tracking) at the analog digital converter (ADC) output.
This study refers to several experiments and data collections performed in interfered areas of downtown Torino (Italy). The
obtained results underline how digital/analog TV transmissions represent a potential interference source for GNSS applications
and might be critical for the safety of life services. 相似文献