I. System Overview The Global Positioning System (GPS) is currently the most highly-accurate means of satellite timing in the world. It has a wide coverage and high timing accuracy, and the C/A code can be shared globally. The 1 pps standard time signal sent by the GPS receiver is the reference standard for the time scale of this scheme. For some military users, 1pps forwarded by BeiDou Double Star can be used as a reference standard.
After the helium atomic frequency standard and the quartz crystal frequency standard are tamed by the GPS signal, its long-term performance has been greatly improved, and the accuracy can be increased by one magnitude, but the price is only slightly higher than that of the locked frequency standard. That is, the accuracy of the helium atom frequency standard tamed by the GPS signal is equivalent to that of the small gong; the accuracy of the quartz crystal frequency standard tamed by the GPS signal is equivalent to the helium atom frequency standard; the short-term stability is basically the same as the locked frequency standard. If you use a GPS signal to tamper with the helium atomic frequency standard and then lock the high-stable crystal, this combination of frequency standard is quite a small high-stabilized bell. Based on this principle, Beijing 7D Aerial Survey Technology Development Co., Ltd. proposed a high-precision combination frequency standard system solution:
Figure 1. System operating schematic
Phase-locked circuit is the key circuit of this scheme. It will be measured by time-difference 1pps and reference 1pps multiple times. According to a specific mathematical model, the data is processed and calculated by the microprocessor, and then D/A conversion is performed slowly. The changing DC signal is phase-locked by the locked frequency, also known as taming. The greater the amount of data, the better the noise can be smoothed, the higher the measurement accuracy, and the frequency of the locked frequency label is closer to the broadcast 1pps reference frequency.
Second, the system performance index GPS combined series of time-frequency standard in addition to the standard frequency (1MHz; 5MHz; 10MHz), second signal, but also the output time encoding code signal, is a wide range of applications, high performance prices Frequency standard equipment.
a) Optional 10,5,1 MHz sine wave b) 1pps(GPS)
c) 1pps (frequency division)
d) 10Mpps square wave e) IRIG-B (DC) time code output f) GPS position output g) The average daily accuracy after GPS lock can reach ± ​​(1E-12),
h) The average daily accuracy after GPS loss of lock can reach ±(2E-11)
i) Stability of time domain frequency: 2E-10/1ms,
5E-11/10ms,
5E-12/0.1s,
3E-12/1s,
5E-12/10s,
5E-12/100-1000s
j) Single-sideband phase noise: 1Hz <-100dBc/Hz,
10Hz <-125dBc/Hz
100Hz <-135dBc/Hz
1kHz <-140dBc/Hz
10kHz <-160dBc/Hz