The SEC Model for Parameters Proposed in ETSI Part 5

Figure 8.7, shows the TDEV of the time error produced at the output of the model for the 1Hz bandwidth SEC using K_f=5953. This is the value suggested by the relation

$$TDEV(\tau\to\infty)=1.075K_f$$

used to propose a value for K_f for a Synchronisation Supply Unit. As may be seen in the diagram, the simulation confirms the existence of the problem with the SEC mask discussed in section 6.4.1. It can be seen that the approximation for the observation interval at which flicker phase noise becomes dominant $\tau_c$ (equation 6.16) is indeed at approximately

$$\tau_c=0.3\sqrt{1+\frac{1}{B^2}}$$

i.e.

$$\tau_c=0.3\sqrt{1+\frac{1}{1^2}}=0.42\mathrm{s}.$$

Since the mask does not represent the asymptotic behaviour of the model, the only way to endure mask compliance is to lower the flicker gain K_f so that the curve remains below the mask.

 

Figure 8.7:   Figure illustrating problem with the SEC wander mask