The multi-tone frequency modulation （FM） signal transferred through track circuit in automatic train control （ATC） system is analyzed. A digital filter with ideal sloping shape in frequency domain is designed for ...The multi-tone frequency modulation （FM） signal transferred through track circuit in automatic train control （ATC） system is analyzed. A digital filter with ideal sloping shape in frequency domain is designed for frequency discrimination. With this filter, the FM signal is converted into AM-FM signal by frequency-to-amplitude conversion. The modulating signal is finally extracted from the envelope of the AM-FM signal. Simulations show that the digital demodulation method could accurately recover the modulating signal in low signal noise ratio （SNR） circumstance, and has good performance in suppressing interference of harmonies of traction current frequency. The feasibility of the proposed method is proved in a hardware system based on SHARC DSP.展开更多
A single-frequency retrievable phase modulated multi-tone fiber amplifier is presented in theory and demonstrated in experiment. A multi-tone seed laser generated by a sine wave phase modulated single-frequency laser ...A single-frequency retrievable phase modulated multi-tone fiber amplifier is presented in theory and demonstrated in experiment. A multi-tone seed laser generated by a sine wave phase modulated single-frequency laser is employed for stimulated Brillouin scattering suppression in an all-fiber amplifier. A demodulation signal which is π phase shifted with respect to the modulation signal is used to retrieve the single-frequency laser from the multi-tone laser. In experiment, we first optimize the all-fiber master-oscillator power-amplifier. With this amplifier, we demonstrate a single-frequency retrievable multi-tone laser with 330-W output when driven by the multi-tone seed, while the ultimate output power is only 130 W when driven by the single-frequency laser. Then, we carry out an experiment for retrieving the single-frequency laser from the amplified multi-tone laser. Results indicate that the single-frequency laser can be retrieved with a sideband suppression of more than 20 dB. Retrieving an even higher power single-frequency laser is possible if a high power demodulator is available.展开更多
Generation of single-sideband （SSB） multi-carrier source based on a recirculating frequency shifter （RFS） is anal- ysed theoretically and realized experimentally. The effects of affecting factors originating from ...Generation of single-sideband （SSB） multi-carrier source based on a recirculating frequency shifter （RFS） is anal- ysed theoretically and realized experimentally. The effects of affecting factors originating from the deviation from the right operation bias voltage and unbalanced amplitude, and the phase of the radio frequency （RF） drive signals on the performance of the multi-tone source are discussed in detail. Based on the theoretical analysis, high-quality 50-tone out- put is successfully realized. Experiments under some implementation imperfections are also carried out. The imperfect and low-quality output results are in good agreement with theoretical analysis.展开更多
The multi-tone interference suppression in HF serial data transmission systemsis analyzed.Analytic expression for the tap weights and minimum mean square errors of theadaptive equalizer in HF serial systems are obtain...The multi-tone interference suppression in HF serial data transmission systemsis analyzed.Analytic expression for the tap weights and minimum mean square errors of theadaptive equalizer in HF serial systems are obtained.The rate of convergence of equalizer indicatethat the equalizer in HF serial system can not only track the rapid variation of HF channel butalso suppress the multi-tone interferences perfectly.展开更多
文摘The multi-tone frequency modulation （FM） signal transferred through track circuit in automatic train control （ATC） system is analyzed. A digital filter with ideal sloping shape in frequency domain is designed for frequency discrimination. With this filter, the FM signal is converted into AM-FM signal by frequency-to-amplitude conversion. The modulating signal is finally extracted from the envelope of the AM-FM signal. Simulations show that the digital demodulation method could accurately recover the modulating signal in low signal noise ratio （SNR） circumstance, and has good performance in suppressing interference of harmonies of traction current frequency. The feasibility of the proposed method is proved in a hardware system based on SHARC DSP.
基金Project supported by the New Century Excellent Talents in University, Ministry of Education of China and the Scientific Research Project in National University Defense of Technology
文摘A single-frequency retrievable phase modulated multi-tone fiber amplifier is presented in theory and demonstrated in experiment. A multi-tone seed laser generated by a sine wave phase modulated single-frequency laser is employed for stimulated Brillouin scattering suppression in an all-fiber amplifier. A demodulation signal which is π phase shifted with respect to the modulation signal is used to retrieve the single-frequency laser from the multi-tone laser. In experiment, we first optimize the all-fiber master-oscillator power-amplifier. With this amplifier, we demonstrate a single-frequency retrievable multi-tone laser with 330-W output when driven by the multi-tone seed, while the ultimate output power is only 130 W when driven by the single-frequency laser. Then, we carry out an experiment for retrieving the single-frequency laser from the amplified multi-tone laser. Results indicate that the single-frequency laser can be retrieved with a sideband suppression of more than 20 dB. Retrieving an even higher power single-frequency laser is possible if a high power demodulator is available.
基金Project supported by the National Natural Science Foundation of China (Grant No.60977049)the Chinese Universities Scientific Fund (Grant No.BUPT 2009RC0413)
文摘Generation of single-sideband （SSB） multi-carrier source based on a recirculating frequency shifter （RFS） is anal- ysed theoretically and realized experimentally. The effects of affecting factors originating from the deviation from the right operation bias voltage and unbalanced amplitude, and the phase of the radio frequency （RF） drive signals on the performance of the multi-tone source are discussed in detail. Based on the theoretical analysis, high-quality 50-tone out- put is successfully realized. Experiments under some implementation imperfections are also carried out. The imperfect and low-quality output results are in good agreement with theoretical analysis.
文摘The multi-tone interference suppression in HF serial data transmission systemsis analyzed.Analytic expression for the tap weights and minimum mean square errors of theadaptive equalizer in HF serial systems are obtained.The rate of convergence of equalizer indicatethat the equalizer in HF serial system can not only track the rapid variation of HF channel butalso suppress the multi-tone interferences perfectly.
