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Problems with the SEC TDEV Wander Mask

 In this section, the shape of the TDEV wander mask for one SDH Equipment Clock will be discussed, in light of the material presented in section 6.4, particularly equation (6.16)

\begin{displaymath} \tau_c=0.3\sqrt{1+\frac{1}{B^2}}.\end{displaymath}

By substituting B=0.003Hz from section 2.4.1 into (6.16) it can be seen that $\tau_c=100s$ for a Synchronisation Supply Unit. By examining the SSU TDEV wander mask from section 2.3.1 presented again as figure 6.2, it can be seen that the flat flicker phase region indeed begins at $\tau=100s$. Thus the mask accurately reflects the predicted asymptotic behaviour of the SSU noise model for salient choices of Kf and Kw.
 
Figure 6.2:   SSU TDEV wander mask
\begin{figure} \centerline{ \epsfig {file=eps/ssutdevmask.eps, width=10cm} }\end{figure}

However, a SDH Equipment Clock has a bandwidth (section 2.4.1 and [5]) given by $1 \leq B\leq 10Hz$. This results in $0.30\leq\tau_c\leq0.42$. Referring to the SEC TDEV wander mask, reproduced in figure 6.3, it can be seen that the flicker phase region also begins at $\tau=100s$ which by the expression for $\tau_c$ shown above would correspond, as before, to a bandwidth of B=3mHz.
 
Figure 6.3:   SEC TDEV wander mask
\begin{figure} \centerline{ \epsfig {file=eps/sectdevmask.eps, width=10cm} }\end{figure}

Thus the SEC TDEV mask does not represent the asymptotic behaviour of an SDH Equipment Clock for any values of Kf and Kw.
next up previous contents
Next: Experimental Results Substantiating the Up: The shape of the Previous: The shape of the
Mark J Ivens
11/13/1997