System functions: Frequency response
This summarises the amplitude and phase response as well as the attenuation curve. The graphs are plotted on a logarithmic frequency axis.
Unlike other graphs, the settings and graph are located in the same window. The lower section contains three graphs: the amplitude response, the attenuation and the phase response.
Only functions containing the variables z and param are permitted – optionally, the variables x and y can also be used as shorthand for the real and imaginary parts. Enter the desired function in the input field for the function, or select one of the existing functions by clicking on the arrow to the right of the input field.
CGRAPH provides optimised displays for the three graphs, which take into account the specified maximum values for the amplitude (logarithmic in dB), the attenuation (logarithmic in dB) and the phase (in degrees). The same applies to the frequency, which is displayed logarithmically to base 10. A ‘-2’ means a frequency of 10-2, i.e. 0.01 Hz, a ‘6’ means 106 Hz, i.e. 100 kHz.
After clicking on the Create graph button, CGRAPH displays the three graphs.
In the example shown here, an increase can be seen in the frequency range of 200 (log(200) = 2.3) – the system function has a resonance point here. Since the attenuation is zero at low frequencies but decreases to a final value of 80 dB (factor 10000) at high frequencies, the system function represents a low-pass filter – a system that prefers to pass signals with low frequencies.
The default values can be viewed in the tree on the left.
The values can be changed later. The graphic is adjusted automatically, but at the latest when the Create graphic button is clicked. Clicking on the coloured symbol for the function, etc., allows you to quickly hide the graphic from the display. Double-clicking on the text allows you to adjust the graphical representation.
The display of the axes is also part of the tree, as the graphics for this graphic type are independent of each other and can be set separately.
Unlike other graphics, an (optional) parameter cannot be varied interactively in the complex plane here – there is no suitable graphical representation available. However, you can enter and change the parameter in the settings area (blue arrow).