Is the gold/silver ratio tradeable?

Take M10's monthly AR(1) coefficient $\hat\varphi = 0.9503$ for $\ln(\text{Gold}/\text{Silver})$ and an illustrative monthly residual standard deviation of 0.05. (a) Compute $\kappa$ per year, the half-life in months and the stationary standard deviation. (b) Compute the expected cycle length (in years) of the cycle strategy between $\pm1$ and between $\pm0.5$ stationary standard deviations. (c) Comment, using Proposition 13A.8, on how reliably such a cycle could be estimated from 25 years of data.