UM2000 signal is a type of multi-audio
frequency-modulated signal which is widely used for railway blocking. Principles
of three typical demodulating algorithms are presented in details in this
paper. Bit error rates of the three methods at different SNRs are achieved by Monte Carlo simulation experiments. Among the three
algorithms, the quadrature demodulation has the best performance at the real
working environment. However, the three methods have the same problem of phase
hopping when noise is too strong.