Velleman PCSU1000 DSO User Manual

Page 16

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PC Oscilloscope PCSU1000

View / Markers (FFT) f & Spectral Density dBV/sqrt(Hz)

This image shows the spectrum of the band limited noise signal.

The analysis of noise in the frequency domain shows the distribution of the noise amplitude as a
function of frequency.

Using the Spectral Density marker and the Frequency marker, the voltage spectral density (VSdBV)

and the noise bandwidth (BN) can be read from the spectrum analyzer display.

First convert the voltage spectral density to

This can be accomplished using the following calculation:

This is the magnitude of the spectrum normalized to a 1 Hz bandwidth.
You may calculate the noise voltage over any bandwidth by multiplying this value by the square root of
the bandwidth.

Assuming a 6 kHz bandwidth, the total output noise voltage is:

(See the V

rms

value of the oscilloscope waveform image of this noise signal.)