A New Method to Measure LF Time Code Service Signal Based on Virtual Instrument

Both of the method and instrumentation for measurement of the low-frequency (LF) standard frequency and time signal service system was proposed in the ITU-R new question draft published in Dec, 2005. Since the foundation of experimental LF time code service station (BPC) by National Time Service Center, Chinese Academy of Sciences in 1998, lots of research have been done in this field. Based on these research activities, a new generation of LF time code service station will run on May, 2007. The widely used method calculates field strength of the LF signal by the level of the received demodulation signal. To avoid the possible measure error in the complicate environment, we should analyse the real measure environment. In the paper, a new method is introduced to measure signal strength considering the characters of the LF time-code signal, which is based on the technology of virtual instrument. The induction signal on the antenna is amplified, filtered and sampled directly. Then, the discrete signal is analyzed and calculated by digital signal processing and adaptive trap filter which restrain the narrow-band interference. We have designed and developed a portable, stable and extendable measure instrument, in which the field strength, the carrier phase and the signal wave is available. It has been used in our practical measurements. The results show that the difference of the field strength measured by Anritsu ML428B and our instrument is less than 1 dBmuv/m . The carrier phase time resolution reaches 1 mus.