This is a live monitor of Japanese Power lines frequency (50Hz.) .

Mains are demodulated by a simple device created by Nara Network Japan. It consist of a down-step transformer that takes the alternate current from the power line (100V) and transform it to 9V AC. Then a full bridge rectifier is added to the circuit to create a semi-DC signal and a capacitor to provide some light initial filtering. A DC voltage divider unit then step down the DC current to fit it for the USB sound card (0.4-0.9V). Finally a passive 2nd order filter around 15Hz cut the 50Hz remnants which at that stage are really negligible, and thus 100Hz becomes dominant.(the Full bridge rectifier double the frequency from the initial 50Hz.). The signal in the first screen is then demodulated using a SL Blackbox and it is possible to see on the spectrum the amplitude-modulated signals coming from the mains. In the second instead, you can see the harmonic of the 100Hz , at 50Hz, still demodulated.

The bottom two graphs are created with a UNIX API and GNUPLOT representing the frequency, phase and histogram frequency detected. The Frequency and phase are calculated by a zero cross circuit united with a custom software. Graphs are UTC time and updated every 20 minutes.(please refresh the page in case is not auto-refreshing). Frequency/Phase graph, together with the histogram one, are reset every day at 00:00 UTC. The total phase graph is updated every 24 hours.

The two systems are independent one each other, each one connected to a different transformer.

The spectrograms are updated every 30 minutes.

The electric frequency is different on either side of the Fujigawa River in Shizuoka Prefecture and Itoigawa City in Niigata Prefecture, with 50Hz in the east and 60Hz in the west. The frequency in Kansai Electric’s service is 60Hz.

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