Print A research team led by Prof. HUA Yu from the National Time Service Center(NTSC), the Chineses Academy of Sciences(CAS) proposed a new method for FM broadcasting timing. The feasibility of this method is verified by relevant experiments and tests, and its timing accuracy can reach sub-millisecond level.
The frequency range of FM broadcasting in China is 87～108MHz, and the channel bandwidth of each station is 200kHz, in which the modulation stereo frequency band is 0～53kHz, and the 54～100kHz frequency band is divided into three additional channels, RDS, SCA1 and SCA2. There are more than 1,000 FM radio transmitting stations in China, and the SCA1 additional channel of most transmitting stations can be used to transmit information.
In order to make more effective use of the existing frequency resources, expand the existing time service methods, combined with the characteristics of FM broadcasting and SCA1 additional channel, researchers encoded the time information and added to the SCA1 additional channel to broadcast with the audio signal; then the receiver receives FM broadcast signal, demodulates FM and SCA1 additional channel, and obtains time information.
FM broadcasting timing method extended the time service function on the basis of civil broadcasting service, and provided a kind of time service with low and medium precision. It provided a platform for the research and application of new radio time service methods. It is a supplement and expansion of the existing time service methods, which improved the use efficiency of broadcasting infrastructure and enriched the time and frequency service system of China.
Part of the research results of has authorized by China invention patent---"A Method of Realizing Timing by Using FM Broadcasting" (Patent Grant Number: 201710115646.8), and published in IEEE ACCESS, the TOP journal of the Institute of Electrical and Electronics Engineers, as the title "Time Information Transmission Based on FM Broadcast Signal"(vol.9, pp.16360-16364,2021).
Figure 1 baseband spectrum of FM broadcasting (Imaged by NTSC) 
Figure 2 FM broadcasting timing modulator and receiver (Imaged by NTSC)
Figure 3 and Figure 4 show the static test results and dynamic test results of FM broadcasting timing method respectively (the transmitting equipment is set up at Laoyingshan FM radio transmitting station in Nanjing City, Jiangsu Province, and the test vehicle moves in Nanjing city and suburb during dynamic test).
Figure 3 static test results of FM broadcasting timing method (Imaged by NTSC)
Figure 4 dynamic test results of FM broadcasting timing method (Imaged by NTSC)