The phase jitter enables to assess quality of signals transmitted in a bi-directional, long-distance fibre optic

link dedicated for dissemination of the time and frequency signals. In the paper, we are considering

measurements of jitter using a phase detector the detected frequency signal and the reference signal are

supplied to. To cover the wideband jitter spectrum the detected signal frequency is divided and – because of

the aliasing process – higher spectral components are shifted down. We are also examining the influence of

a residual jitter that occurs in the reference signal generated by filtering the jitter occurring in the same signal,

whose phase fluctuations we intend to measure. Then, we are discussing the evaluation results, which

were obtained by using the target fibre optic time and frequency transfer system.