# Spectrogram, part 1

The figure below shows infrasound signal produced by a typical wind turbines. On the horizontal axis there is frequency in Hz 0 – 5 Hz. The vertical axis represents time in hours 00: 00 – 24: 00.

Infrasound strength is described in colors from blue to red. Red is strong signal.

Measurement performed on living spaces. The nearest power plant is approximately 1,37 km. The spectrogram signals the intermittent signals under frequency 5 Hz.

Figure:

1. 1. Wind turbine basic blade frequency. This 0,6 Hz.
2. 2. The second harmonic which is 2 *0,6 Hz = 1,2 Hz.
3. 3. The third harmonic.
4. – 8. 4. Higher harmonic frequencies

The following figure shows the same measurement in the 0-20 Hz frequency band.

NOTE! Infrasound frequency range comprised by wind turbines is mainly less than 5 Hz .

The following figure shows the wind turbines stop a little before at 11: 00.

The following figure shows the same measurement in 0-20 Hz band.

The figure below shows measurement results during the same date and from 5 km distance to the same power plant.

The figure above shows the horizontal lines caused by normal housing disturbances, mainly due to closure of the doors.

The following figure shows the same measurement in 0-20 Hz band.