Measured signals of the 1 pps system clock (top) and first LO signal generator’s reference trigger (bottom) of the Nobeyama |$45\:$|m telescope in volts. The left panels show them over a |$\Delta t = 150$| ms duration, where the 1 pps signal rises at |$t=0$| ms, while the trigger signal, which is synchronized with the 1 pps clock, falls. The subsequent |$\Delta t \simeq 8$| ms voltage dropping at 0 V is attributed to the settling time of the signal generator, where it does not generate a signal for the LO; thus, the SIS mixer is unavailable. The right panels show the same results, but over a |$\Delta t = 2$| ms duration around |$t=0$| ms, which demonstrates that the time synchronization error is much better than |$200\, \mu$|s, the period of a slope. (Color online)