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利用两个地面站的位置是已知的这个事实,美国国家标准局(NBS)提出了一种全球定位系统(GPS)信号在专用存取信道中的特殊应用问题。因此,如果从这两个地面站观察同一卫星,就有很好的时间传递能力。NBS 研制的一种原型接收机的特点是时间传递精度极高,而且成本低。即使不知道通过接收机的绝对时延值,人们也能通过了解两个接收机之间的时延差而进行绝对的时间传递。从接收到的卫星信号所得到的接收机输出端的均方根时间起伏值好达3.5ns,这是由于使用了平均时间为15秒全向天线的缘故。这噪声被表征为白噪声调相,此噪声经过平均可以低于系统噪声,而系统噪声在环境温度为几度范围内大约为1毫微秒。测量 NBS(博尔德市)和美国海军天文台(USNO,华盛顿特区)之间的时差,得到的天与天之间的时间起伏约为5ns。将软件与接收机组合成全自动的系统,用 Z80A 微处理器来调整接收机锁相环的幅度和调整合成器,对额定的多普勒偏移进行校正。该接收机还有一个突出的特点,就是可以利用微处理器来校准0.1ns 的内部时间间隔计数器。用户所需要的只是一个本地的秒脉冲信号、一个5MHz 的信号及其本地坐标。
Taking advantage of the fact that the locations of the two ground stations are known, the National Bureau of Standards (NBS) has proposed a special application of the Global Positioning System (GPS) signal in a dedicated access channel. Therefore, if one observes the same satellite from both ground stations, there is a good time to pass on. A prototype receiver developed by NBS is characterized by extremely accurate time delivery and low cost. Even without knowing the absolute delay value of the receiver, one can also make an absolute time pass by knowing the difference in delay between the two receivers. The rms time rms value at the receiver output obtained from the received satellite signal is as good as 3.5 ns due to the use of a 15 second omni-directional antenna. This noise is characterized as white noise phase modulation, which, on average, can be lower than the system noise, which is about 1 nanosecond at ambient temperatures of a few degrees. Measuring the time difference between NBS (Boulder City) and the United States Naval Observatory (USNO, Washington, DC) yields about 5 ns of time between days and days. The software and receiver into a fully automated system, with the Z80A microprocessor to adjust the receiver phase-locked loop amplitude and adjust the synthesizer, the rated Doppler shift correction. Another prominent feature of this receiver is the ability to use microprocessors to calibrate 0.1 ns internal time interval counters. All you need is a local seconds pulse, a 5MHz signal and its local coordinates.