"Toonfrequent" / Ripple control, May-June 2021

Pieter-Tjerk de Boer, PA3FWM pa3fwm@amsat.org

This page documents some measurements of the "toonfrequent" signals on the power grid. These signals, also known as "ripple control" in English or "Rundsteuertechnik" in German, are tones of several hundred Hertz, which are used to remotely toggle electricity meters between high (day) and low (night) tariff, switch street lights on and off, etc. In the Netherlands, these signals are about to be switched off on July 1, with the exception of streetlight control. So, high-time for a first look at them.

The following plot shows a spectrogram of the grid voltage. The horizontal axis shows time in seconds (from some arbitrary starting point), and the vertical axis frequency in Hz. The brightness shows the strength of the signal at that time and frequency.


The continuous lines at 50 Hz and its multiples are simply the 50 Hz 230 V power as delivered by the grid here. In theory it's a sine wave (so purely 50 Hz), but all kinds of equipment nowadays distort the sinewave, producing harmonics. The toonfrequent data signals are the interrupted lines, looking a bit like morse code signals with dots and dashes.

Analysis of these signals, recorded between May 9 and May 24, 2021, reveals the following:

As noted above, some messages recur on a daily basis but not at exactly the same time. Here's a plot of the timing of many such messages in the evening, roughly around sunset time: [times of daily variable messages] Red, green and blue lines are for messages on 228, 183.3 and 226.6 Hz, respectively. The orange line indicates the time of sunset in the middle of the Netherlands, and the yellow line the time the streetlights in my street switched on.

Clearly, most but not all of the lines follow the sunset time, either smoothly or which lots of variations. The latter presumably are controlled by light sensors and thus depend on the weather. The streetlights in my street don't seem to be controlled by any of these signals though.

Besides their timing, another interesting aspect of these signals is their strength (amplitude). The following set of plots shows the amplitude (in volt) of the signals on the four frequencies as a function of the time of day. [plots of amplitudes] Some observations:

There are still many questions open, such as:

...To be continued...

Text and pictures on this page are copyright 2021, P.T. de Boer, pa3fwm@amsat.org .
Republication is only allowed with my explicit permission.