On-off intermittency is observed in a mutually coupled phase-locked loop (P
LL) system for both experiments and simulations. The system has two coupler
s between two PLLs for coupling and is designed to give good correspondence
with dynamic systems with a periodic potential. In simulations, numerical
calculations are performed on the governing equations of the PLL. In experi
ments, PLL IC modules and op-amps are used as PLL-cores and key components
of couplers, respectively. The simulation results show coincidence with tho
se of experiments. The properties of the burst signal in the observed inter
mittent signal are: the -1 power law of the amplitude distribution; and the
-1.5 power law of the laminar duration time distribution. The power laws a
gree with the proper statistical features of the on-off intermittency.